VW Mk4 Golf Estate 1.9SDI
 

Hello all, I own a VW Golf Estate in the UK (would that be Rabbit Stationwagon or Golf Variant overseas?). As the first wave of Fuel Duty increases has taken effect today, VAT increase on the 4th Jan and a further Fuel Duty increase later in the year, I thought it would be time to see what I could do to save fuel money by making it go further.

I drive about 10k miles per year and already follow many of the fuel saving driving techniques. Documented fuel consumption is 44MPG on a mixed cycle but I can easily achieve 53MPG and can approach 67MPG on highways at 65MPH average. I never exceed 2000RPM except in 5th gear.

I've already ordered a suspension lowering kit (aluminium body coilovers) which not only increase aerodynamic efficiency but also save weight on the steel originals. I've been trying to find lightweight lower control arms (pressed steel) and hubs (cast iron?) but no luck so far, plus there's a huge potential saving in the rear suspension system. Continuing the weight saving theme, I've dumped the spare wheel and bought a couple cans of tyre weld and a 12V air compressor. I've also bought some cheap used alloy wheels from an Audi A3 and increased pressures to 45PSI.

Planned mods after fitting the suspension upgrade is to convert to 100% biodiesel, saving me at least 25% on fuel costs. Also to continue with a few aero mods and any more weight saving mods I can easily and cheaply do. One of those will be replacing the wing mirrors with smaller DTM Cup mirrors which are about half the area of the originals. And, by careful scanning of ebay, I'd like to find some even lighter alloy wheels and cover with smooth discs, and maybe reduce the width of the tyres from 195mm to 165mm. I'd really like to know how to ease the airflow over the wipers, if anyone knows?

Also, does anyone know if it's worth swapping the hydraulic power steering to electric? The pump robs nearly 8HP under load (and a coresponding amount of fuel) and even when not in use still uses power to pressurise the system. Obviously this will put more load on the alternator but is the trade-off worthwhile? Also, on an alternator related theme, I could change the rear lights for LED versions and the headlights to 35/35HID bulbs. How much of a saving on the alternator load (and fuel) would this be?

I have a few engine mods planned - most dramatically the bio conversion. But I also want to find out if the ECU can be mapped for economy, and find out if there are more efficient fuel delivery systems available (injection system)? This is my first diesel so I'm also keen to find out if there are more efficient inlet and outlet manifolds, if anyone knows?

So, to recap, I've broken down my mod categories as follows, in priority:
1. Engine efficiency
Biodiesel conversion
ECU remapping?
Fuel delivery/manifolds?
2. Aerodynamic efficiency
Lower suspension
Smooth wheel covers
Smaller mirrors
Wiper, vent, etc mods?
3. Weight savings
Remove spare wheel
Lighter, narrower road wheels
Replace heavy components?
4. Systems refinement
Electric power steering?
High efficiency lighting?
(the question marks are those mods that I'm not sure if they are worthwhile)
Are there any other mods that are proven to be cost effective?

I'm now off to read the forum stickys so I may well end up answering my questions, but feel free to chip in and add to my list.

Cheers, Steve.

What year is the car?
It seems like alot of cars have power steering and didn't really need it, so you might check around and see if there is a non power steering rack standard on other versions of the Rabbit that would bolt right on.
Also be aware that some alloy rims are heavier then steel rims, finding out the rim weight is always a good idea instead of just assuming that alloy rims are light.

Hello Ryland

It's a 2000 non-turbo diesel.

I'd probably need some form of power steering as the engine is in the front and it weighs as much as an elephant. I was just asking which is more efficient: hydraulic or electric power steering. I found a post here that says electric is more efficient as the hydraulic system is always being run whereas the electric system is only 'on' when you turn the steering wheel. That's good to know, I just have to work out the cost/benefit ratio and find somewhere that sells the conversion if it works out favourable.

Yes, I will see what size wheel I can get away with (larger the better) after the suspension upgrade. Currently 15" wheels with 65 tyres (stock) but I may go to 16" thinner wheels and lower profile tyres. I've found WheelWeights dot net as a good source of weights for a large range of wheels. I need to find the same for tyres.

Cheers, Steve

A quick update and a story.

In addition to the suspension upgrade, I have now purchased a ScanGuage2 monitor and a pair of DTM Cup mirrors. Before I fit anything (other than the ScanGuage) I will do a few runs of mixed driving, mostly 100 mile day and night trips to get a fair result, and measure the MPG. I'll post all results here. I'll then complete all aero mods and note any changes.

An interesting story for weight savers. A friend of mine is restoring a classic car. He's stripping it completely and part of the process was pressure washing the underside. As an experiment he decided to weigh how much dirt and crud that came out - 12.5Kg! That's nearly 30Lbs of free weightsaving just by removing the dirt. Moral of the story: wash your car regularly to save weight.

Cheers, Steve

Hi Steve,

Good to have another brit on boarxd especially someone with a non-whirly 1.9 (granted yours s a bt more advanced than mine!)

the Power steerng is six/two-threes really and if your doing a lot of motorway its are that the it'll even kick in.

loving the the DTM mirrors idea, I'd try a grille block too as its one of the qickest ways to improve the aero and it can be done subtly , I'm guessing you're going for looks too!

Which 16" A3 alloys are you running? got to admit I'm intriged!

Start your fuel log soon - there is a a lot of potential in that there ride!

Hello Rob, compadre!

About the power steering, my thinking is that the pump is continually being turned, therefore taking HPs away/adding to fuel consumption. The good thing about electric power steering is that the alternator is turning anyway - to charge the battery, etc so it doesn't matter if I load it a little more with a power steering motor. But my logic could be flawed?

At the mo I have 15" Audi alloys (take a look on fleabay at item no. 390276194556) but I'm thinking of getting bigger wheels if lowering doesn't fill the arches.

I'm trying to look for an aftermarket grill/bumper/spoiler combo that is mostly filled for neatness. I'd like to do it myself but I know I'd end up with pipe wrapped around my pulleys! I need to take the roof rails off and somehow make the wiper area more aero - there's a huge gap between the bonnet and the screen that just sings out 'turbulence'... With the addition of smooth wheels, all my aero mods would be done. I'd love to shave the door handles and grind off the gutters and seal the seams but that is a few steps too far for me.

I'm looking forward to getting the ScanGuage prior to making any mods so I can have a measurable and standard baseline to compare against. I'll do about 400 miles to provide my baseline. I may also start using biodiesel at the same time too.

Let me know of any tips you've picked up and what you think of the fuel price rises and what you're doing to combat them.

Cheers, Steve

Personally i think its time to get militant again. increases in tax, VAT etc the country won't be able to afford their own bills let alone the countries!

lower tax - which will increase sales, increases demand = more jobs

15% of something is better than
20% of F*** all

I just thought, for any project you need to set yourself some goals and boundarys, so here are mine:

Goals
To keep her a reliable and practical family car
Increase economy to 60mpg (UK) on an urban cycle
Increase economy to 80mpg (UK) on a highway cycle
To spend no more than £1000

The scanguage is going to be your key tool here.

From my toying around with my TDI, I've found that just having good instrumentation teaches you the best way to drive more efficiently, and that makes the single biggest difference (and probably the second cheapest).

Given it's winter all around the northern hemisphere, blocking your grill, aggressively, will help with warmup times. My own setup on my 2000 TDI, consists of a 2/3 block with coroplast, left and right thirds of the radiator behind the grill openings (painted black so they're not visible from the outside).
I run with 1/3 or 2/3 block next to the radiator year round.

The bottom opening on the 4th gen VW Golf/Jetta tends to give the best airflow for cooling. If you don't need that due to the cold weather, you could readily block that up that opening itself.

If you want to be careful, block this opening progressively, and monitor temperatures. And aim for the ability to quickly remove out segments as needed. My first lower block was black plastic stretched taught over the black plastic insert in the lower opening. The time I did have higher temperatures and high humidity (98°C coolant, with 30°C air temperatures, at highway speeds), I simply opened up the plastic with a hole in the center using a pen knife. :P

Remember this is just information from a forum post, not a carefully controlled study, and you live in another region of the world, your mileage may vary with this tip, etc., etc.

Thanks for the excellent advice Chris, and also for clearing something up. I thought blocking grills and vents was purely aerodynamic, not to get the engine to temp quicker. Thanks again!

Yes, the ScanGauge is what I need first. I used to drive a VW Tuareg 3.2 V6 petrol for a few years. During the last year or so I eventually found the fuel usage section on the computer and WOW, was I surprised. My lifetime average was 18mpg! From using the live display I was able to learn to drive economically and I carry that through today. I was footloose and fancy free then, now I have a child and financial responsibilies so every penny counts!

Thanks again for the advice, Steve

Sticking to 60-65 mph on the motorway gives a big gain.

It helps - every little bit helps - but don't expect miracles from it.

Same with the weight removal.
It helps, but it helps mostly in city driving. On the motorway you'll be hard pressed to see any + effect on fuel consumption.

So don't pend too much on these, as you're unlikely to regain the investment through the reduced fuel consumption (FC).

Light wheels with small openings are a bonus.

And burning a renewable fuel.

Same here.
When you need new tyres, fine, go ahead (if 165 is OK with the MoT).
If you buy them to reduce your FC, you won't get the investment back through reduced FC.

Buy LRR (low rolling resistance) tyres when you need new tyres.

It already happens naturally as it's a high pressure area at the bottom of the windshield, but if you want to improve it further, you must somehow add a gentle upslope on the rear of the bonnet.

It's been done and it results in lower FC, but it's not exactly an easy modification.

The numbers are out there on this site, it isn't really that much.

Most remappings are done for more performance, but they often have the side benefit of reducing FC (as an example, Rica claim 5-10% better fuel efficiency), especially when you hypermile the car .

The VW injection system is already very efficient.

Before jumping in headfirst and buying all sorts of stuff to modify the hardware, modify the nut behind the wheel ;) and do the cheap mods.

- grill block; air dam; shut off the airco if it's still on; covered wheels;

- drive slower on the motorway (driving 70mph / 110kph on the British motorways is what got me started on this ecodriving thing ;) ); idle less; start coasting if you're not doing so already; eco-parking (manouevring with a warm engine rather than a cold one); ...

Go through the hypermiling tips for even more hints :
100+ Hypermiling / ecodriving tips & tactics for better mpg - EcoModder.com
... and through the vehicle modding tips :
65+ Vehicle modifications for better fuel economy - EcoModder.com
... to see what you can easily change.

I go over them every now and then to add more tricks to my driving style once the other tips have become a habbit.

Don`t forget about underbody aerodynamics.
I know WV has plastic panels beneath the engine, but there is always room for improvement, for instance check the rear if it`s parachuting. A good underbody is worth a lot more than removing mirrors or masking wipers.

WOW thanks fellas, especially Euromodder! I think you've answered nearly all of my questions! Thank you VERY much.

To follow up on a couple of your suggestions, yes I am very aware of what sort of nut I have to adjust behind my wheel... My previous car was a very thirsty 4x4 with a massive fuel tank that needed filling constantly! By finding out exactly how much fuel I was burning (and how much that was burning my wallet) I decided to change the way I drive, using the on-board computer. The ScanGuage will do exactly the same for my current car. I can't wait to instal it and varify my estimated fuel consumption figures.

Also, I don't want to spend £1k - I want to spend as little as possible, otherwise the payback period could outlive the life of the car.

One interesting point, I drove 100 miles to my mum's house today at a steady 65MPH and achieved about 66MPG starting with half a tank and about 100Kg load. On the way back, and as VAT is going up tomorrow, I decided to fill up to take advantage of the lower fuel cost - about 43 litres. When I got home I calculated that I probably only achieved about 63MPG - and I only had a 20 kilo load on board. I can only conclude that driving with more fuel than you need is very wasteful indeed.

Cheers again, Steve

Here's my costs so far. I don't know whether to include the cost of the car as I had it already as our family car - I didn't buy it for the purpose of an experiment or project. I'll include it anyway:

£1750 VW Golf IV 1.9SDI Estate
£ 119 ScanGuage II trip computer
£ 145 Alu Coil-over suspension lowering kit
£ 40 Audi A3 alloys
£ 30 DTM Cup door mirrors
£ 7 12V tyre inflator compressor (saves spare wheel)
£ 5 TyreWeld can (get me home fix in case of puncture)
£ 346 Total

Before I spend any more (or install anything except the SGII) I will do my benchmarking starting in a couple weeks with a 120 mile trip to Bristol, and 120 miles back again! Then another 200 mile round trip south.

Cheers, Steve

Proposed plans for my Golf. This is not my car, mine is black, but you get the idea.

http://golf.citrusdm.com/

i have experience with the OEM on power steering systems. The short answer is removing it should net you ~2MPG. Most cars can work without any power steering but if you must have assist go electric. it costs $500 more new (to the OEM) but they claim it helps the MPG by 2 and drops about 30# of weight.

All my parts have arrived finally. I'll be testing out the ScanGuageII at the weekend ready for a long drive the following weekend. At last it starts to get exciting!

I just took the powersteering belt off. Easier to test that way do you need the steering or not. I did not need it with my arm forces, but I am a quite big guy...

Non powersteered rack migh have different gearings still so you need to test a car with no powersteering and make your decicions after that.

On my car the effect was minimal 0.1-0.2 liters.

caster and a feww other Geometry items may be different on a non power steering car too

Well, either I own the most economical production diesel car in the world or my ScanGuage is off. I did a 291 mile trip and my average consumption was 0.8LHK. All that money VW spent on the 1 litre concept car - they could have just borrowed my car!

I'll do another fill up tomorrow and calculate using traditional methods. I will recalibrate at this stage too. My fuel gauge reads half a tank left (a full tank is 55 litres) so that's 25.5 litres used in 291 miles (468km). This is a very rough calculation though.

More later...

I think it could also be that the wind direction was less favourable on the return trip - weight doesn't affect steady speed fuel economy much.

Partly correct. It's effect is minimal on a FLAT surface but there's nowhere I go that's flat. Or doesn't have an amount of city driving at either end. In my journeys, weight is an issue.

A full tank will take me close to 600 miles. My longest journey is a 240 mile round trip so, accounting for detours, etc, half a tank should do me fine. However, while I'm calibrating my ScanGauge I will continue to fill up until I get accurate readings.

Thanks for your input though.

I've finally refilled to show the following data:
295.7 Miles
22.1 Litres of diesel used
All driving was done in almost identical weather and wind over 2 days. The car had 2 adults and one baby, plus all paraphanlia that goes with an overnight stay with a baby ~100kg.

My calculations are:
13.38 miles/litre
21.53 km/litre
4.64 litres/hundred km
60.83 miles/gallon (UK)
50.65 miles/gallon (US)
I used about half a tank of fuel and filled up at the same pump.

Edit: I was travelling at a motorway speed of 65mph with a downward variation of up to 10mph on hills.

Another 200+ mile round trip coming up this weekend so will use that to prove figures above. I also have a 150 or so mile trip next weekend to act as a double check. After that the mods begin to be put on. I'm hoping for some improvement, though I can't complain at what I already have.

Hi - Just read your thread with interest as I have exactly the same car - Golf IV estate 1.9 sdi estate from 2001. I was previously running an old W124 300d merc on veg oil - did 40k miles over 3 yrs but unfortunaltey just lost my main veg oil supply and needed to get a replacement pronto which would run very efficiently on regular Diesel.

Only had the golf a few days and am curious as to the rpm of your engine when at 60mph in 5th gear. I'm sure mine is near 3000 rpm which seems a bit high for such a speed.....

I am yet to work out my mpg figures, but will be soon.

Many thanks
Rik

Hello Rik

I haven't updated this thread for a while but have been updating my fuel log as I fill up. I recently had a full service done (£1400!!!) and found lots of problems, particularly with suspension, which had to be replaced. Luckily I had already bought a lowering kit - all good quality coil over shocks - from Belgium. That whole kit cost the equivalent of one set of VW spring/shock so at least I saved something. I also had the oil replaced with synthetic to reduce friction. It was always a good runner, being a fairly low mileage car, so I can't say that I've noticed a difference in the drive at all. While they were servicing I also asked them to replace the wing mirrors with aero DT Cup style mirrors to reduce drag.

The result is quite disappointing. I was regularly getting 60mpg (UK) at 60mph before the service and that figure has stayed the same. The only difference is that I can also now get 60mpg at 70mph, where before I was getting closer to 56mpg. So it looks like the aerodynamic performance has increased, but the economy has stayed the same. I'm a little confused by this.

To answer your question, at 70mph my rev counter says just under 3000rpm and I think at 60mph its about 2600, or close to it.

I'd be interested to hear your stories on running veg oil. This is something I definitely want to do - at least some cheaper alternative for diesel.

Please keep in touch as I'm sure we can work together to find some fuel saving tips for our cars.

Regards,
Steve

Oh, I forgot to mention that I had my car lowered by 5cm when fitting he replacement coil-overs. A bit scary going over speed humps but at a slow speed it's fine.

Cheers Steve,

My cars RPM \ mph figures are a little different.. not sure why
2600 RPM = 55 mph, 3000 RPM = 60 mph and just over 3200 RPM at 70 mph.
Bit odd and I'm sure doesn't help my fuel efficiency. Just wonder if at somepoint my car has had a replacement (mis matched) gearbox !!

Dont want to be a pain but would you be able to double check your reading as this does concern me a little.
I have a 100 mile trip tomorrow and i'll see what my mpg figures are, I suspect not so good.

Regarding Veg oil. Before I lost out to commercial collectors i was collecting waste used veg oil from pubs for free.
My Merc W124 300d merc loved the stuff straight. over 3yrs years and 40 k miles the engine still runs like a dream i will be gutted when i finish up the last of my 200 ltrs of oil

The old diesel mercs eg W123s and W124s were perfect for veg as they have a bullet proof fuel pump and are indirect injection - these cars will run unconverted with no engine mods at all. (got mine off ebay for £800)
Also some older Peugots and Citroens 1.9TD were good as they also has indirect injection (as long as they have the Bosch and not Lucas fuel pump)

More modern diesels like ours are direct injection and not so good - but can be converted to run on veg oil perfectly fine - needs a twin tank conversion and few other bits.. if i get a veg oil supply i will be doing this to the golf - kit cost approx £400 and a bit of technical know how.

The vegoil forum is a must read and a goldmine of info
vegetableoildiesel.co.uk

Hope this helps a little
Cheers
Rik

It's been nearly a year since my last update so has given me plenty of evaluation time for the minimal mods that I have made.

While driving a steady 40-50MPH I can easily achieve 3.6LHK (65+ MPG US / 78+ MPG Imp), and driving at 70MPH will return about 4LHK (58+ MPG US / 70+ MPG Imp).

This has been achieved in 3 ways:
1 Regular maintenance servicing using quality oils (the car is trouble-free and rolls forever!)
2 Inflating tyres to 45PSI (low rolling resistance)
3 Lowering by 4-5cm to encourage more flow over or around the more aerodynamic surfaces

The only way I can dramatically improve these figures is to have some sort of electric assistance for pulling away from lights or junctions – this is my only major use of fuel now. Other than that, I can reduce fuel costs by converting to an alternative diesel. I've not considered fitting a supercharger/turbocharger or to use one of these performance chips. Any advice or experience gratefully received.

I have the same car - a 52 plate.

My consumption is similar to yours, but using my Ultraguage I am doing things that I would'nt have thought of before. Like driving at 40 in 5th gear and seeing an indicated 110 mpg !!

My tyres are Michelin Energy Savers at 40 PSAI, and I have an almost full grill-block - just the very lowest slot in the bumper is open. This halved the warm-up time in the cold weather. I do hope to try adding an air dam and rear wheel skirts, but there is no doubt at all that it is driving-style that makes the biggest difference!!

I am a driving instructor, so by hypermiling between lessons I can still get something like 50mpg (imp) from tank to tank!

Cheers from Cambridge :thumbup:

Good news Kingsway. I also change gears when most efficient to do so (around 1800-2000RPM in my car) so I'm in 5th at 30MPH and being so freewheeling I don't have to apply much power to maintain that speed.

I don't yet have energy saving tyres but I do get good part-worn tyres to replace the old ones. This save a huge amount of money over time as I treat them well and they last as long or longer than new ones if properly maintained and inflated.

It's been a comparatively mild winter so didn't go for the grill block. You'll have to tell me (or show me) how you did yours. I have a spare in the house somewhere that I can modify.

And you're right, the real number 1 fuel-saving method is driving style, it makes such a dramatic difference. Would be good to swap stories and mods. I bought replacement components for my entire suspension to fully adjustable coil-overs for less than the price of 1 original VAG shock!

The 'stealers' do know how to charge for spares and service all right!

On my last MOT the cat-convertor was loose due to a broken bracket. Vindis wanted to supply a new cat and pipe for approx £1000.00 - I went to the local Kwik-fit who welded it up for me for £20.00 - job done! :thumbup:

I can't say I've seen much difference in FC since adding the grill block, but when the weather was at or around zero degrees C, the car would warm up in about 5 minutes instead of the usual 10+ minutes.

I used some black Correx and zip-ties for the lower grills. For the main grill I folded some foam sheet that had been used as packing in a parcel, and squeezed it between the slats. Looks a bit tatty.... but very quick and easy to remove! I also put the under-engine cover back on... which I was lazy enough to leave off after the previous oil-change.

BTW I think our car - or a TDI version at least - were marketed in the US as both 'Jetta' and 'Passat' at various times.

Richard

Very interesting to find your postings 1.9SDi.
 

Very interesting to find your postings 1.9SDi.

I have a 2002 Golf 1.9TDi Estate and I've been tweaking it over the past year or so for economy. So far I'm averaging about 75 mpg Imp overall with a mix of driving, and more on long journies.

(I found your post because I need to replace my rear shocks so I was looking at upgrading at the same time.)

My best ecomod so far has been modifying my driving style. I cruise on the motorway at 50mph and I find the mpg starts to drop off dramatically even at 55mph.

Next best thing was to keep the engine temperature nice and warm. I totally block the entire grille in winter and almost totally block it in summer. A thermostat change was also required but in winter the engine just doesn't get up to temperature, and that impacts mpg. (The 'idiot guage' on the dash is designed to show '90' at any temperature between about 75 and 107 degrees, but below 90 degrees it doesn't run efficiently.)

One tip I can give you is to replace the gearbox oil. VW say you never need to but after 150k miles I decided to do it anyway. I got the right stuff from VW, a small tube of Molyslip gearbox additive (from Halfords) and got my mechanic to do the change. Once up on the ramp it took him ten minutes and he charged me £15 labour. The difference was immediate and obvious. The car clearly rolled much better - especially when coasting in neutral - and mpg (as displayed on the dash) was up by a full 5%.

I use low rolling resistance tyres and pump them up to the maximum allowed on the side wall, which is 51 psi. I will probably drop the rears back down to 45 or so but keep the fronts at 51. I find the car handles way better: steering is lighter, the car doesn't 'wallow' into corners and I've also found that it maintains speed much better when going round roundabouts and so on. I use the stock alloys and 165/65 R15's.

I also use BP Ultimate and that helps mpg a lot - pays for itself anyway. I've never tried it but I suspect that using standard diesel and adding Miller's additive/cetane booster would produce similar mpg gains at a lower cost. Millers does not improve mpg when used with BP Ultimate, but using 1 part acetone to 1000 parts diesel improves mpg by a couple of percent.

Not sure what else to add right now but if I think of anything I'll post again. Did you ever get rid of the hydraulic steering gear? Having harder tyres is always going to help as steering is so much lighter, but Golfs have always been notorious for having heavy steering. Not sure I would want to do without. I had a N/A Astra 1.7 diesel with no power steering and that was fine, but Golfs, ...nooo...!

I'm currently experimenting with engine remapping but the results are not encouraging so far. My guess is that if you normally drive slowly anyway - drive for economy rather for speed - then the economy gains with remapping will not impress, but if you are frustrated with lack of power and so tend to thrash the engine regularly, a remap with more torque can result in a more relaxed driving style and so can save fuel. But that's just a theory. I'll persevere with remapping for a while and see if I can get some gains that way. It might be the first remap was not quite right and they need to do a bit of tweaking.

I regularly drive in 5th gear at tickover speed in 30mph zones - i.e. 850 RPM and 26/27mph (traffic allowing). On the flat the engine is nice and smooth at that speed and the mpg meter goes way off the scale and pegs at 99.9mpg average. (Oh, but before I changed a failed alternator the engine was rougher at that speed and I was getting (showing on dash) more like 95mpg average at 27mph. Turned out the alternator pulley freewheel was stuck (didn't even know there was a freewheel pulley!) causing the rough idling and lower mpg at tickover.)

(By the way, my dash mpg gauge is about 7% optimistic. Useful for before-mod/after-mod comparisons though.)

I thought about ditching the spare wheel but decided against. I lost a tyre in a blizzard one dark night on a country lane a couple of years back, and without having a spare I would have been stuck. The RAC would have been 'snowed under' (ha ha) that night as it had just started snowing heavily and they would have taken hours to get to me. The tyre had ripped right away from the rim so tyreweld would have been useless. Nice idea but no, I'm going to stick with a proper spare (I also carry a breaker bar with wheel nut socket, a pair of wheel chocks, a jack, a foot pump and a can of diesel.) Every little helps but the maximum possible theoretical fuel saving from leaving a spare wheel out is the proportion of the total vehicle weight that the spare wheel represents. That's maybe 1%. But that saving would only apply to acceleration. At constant speed, friction and air resistance play a larger part than weight so ditching the spare tyre will save maybe 1/2% on fuel - or about a quarter of a mile per gallon. Now, running on a nearly empty tank most of the time could save a full 2% in fuel. My dilemma is that it is much easier to MEASURE mpg if I fill to the brim each time.

Thanks for your interest and post Paul, it's always good to hear of others stories about a similar car.

I haven't done anything else to my car since these posts but I am still keen on at least a partial grill block (the lower vents under the bumper – I don't have fog lights in mine) and some sort of flexible dam under the front chin.

I've lowered my car by 5cm and I can honestly say it has improved the aerodynamic performance to the point that I can drive approx 10-15MPH faster for the same fuel usage. Long runs at 70MPH are at around 3.2–4 L/HK (88–70 MPG Imp) depending on route and weather conditions, as calculated by calibrated ScanGauge II. Fitting a front air dam will improve this slightly more. The problem with being so low is that I am affected by speed bumps grounding the car, so I have to be very careful.

I haven't investigated engine mapping or fuel additives but I did a test of the higher grade diesel but (for whatever reason) it didn't work out financially viable for me. Very minimal economy gains of >2% max.

The car is regularly serviced and lubricated and tyre pressures are checked monthly – it's about time I checked them now actually. Free-rolling is effortless to the point of having to apply brakes occasionally.

I did briefly look into more weight reduction a while ago, with a carbon fibre or fibreglass bonnet, racing perspex side window replacements, etc but the cost is prohibitive and would take many years to pay back. Everything I don't need is taken out – spare wheel included, so I carry a can of Holts and an air pump, which I hope will see me to a garage, except in a derimming or catastophic tyre failure. I also run with a half tank which easily returns me approx 400 miles.

Are you a steady accelerator or an instant one? I've been experimenting with both methods – using economic gear changing at minimal accelerator levels to gain speed and also just shooting up to speed limit and cruising. From initial testing (not exhaustive) getting up to the speed limit quickly, if it is 30-40MPH seems to be more economical, but this gain fades slightly if speed limits are higher, and disappears completely if it's to 70MPH. Have you tried this?

Cheers, Steve

Hi Steve, so you still have the SDi then. I'm jealous. No turbo, no intercooler, no temptation to step on it and use more fuel. Less weight, more space in the engine bay. Less to go wrong. Nice. Not so many SDi's around in the UK.

Actually, since you don't have an intercooler, I think you can block off the lower grille completely - and I would suggest semi-permanently - with no issues at all. Mine is in fact blocked with plastic sheet secured by black PVC insulating tape (it's a black car so it looks fine) but I realise that it blocks the cold air from the intercooler, which might not be ideal. The way I drive though, I so seldom use the turbo that I think it probably makes very little difference in my case. (I blast the engine briefly once a week or so just to blow any soot out and to make sure the turbo parts (vanes?) don't seize up.)

If you have Scanguage (I don't at present) then you will know what temperature your engine coolant gets to. Does it stay up at the correct temperature (90+ degrees) with the grille open? I guess it might do in the summer. Over last winter I had the grille completely blocked (apart from the engine air intake of course!) and that worked fine for me. I did experiment with keeping the 100% grille block in the heat of the summer, and although the engine coolant temperature never rose above 100 degrees even when it was 30 degrees outside (I use VagCom to measure) the air temperature in the engine bay rose to over 50 degrees at times and I decided to unblock just the uppermost row in the main, central, upper grille, just for the summer. Come the autumn, it will get wrapped up warm again until late spring. Maybe different engines behave in different ways but for me that's the only way to get - and keep - the engine up to proper temperature in winter. And that makes a quite marked difference to fuel economy. (And no, there's nothing wrong with my thermostat - the engine simply doesn't create much heat!)

Your mpg for a steady 70mph, by the way, sounds astounding. My mpg is great up to 50mph and then drops off markedly even at 55mph. Sounds like the lowering really did work. It occurs to me that the new suspension components might just work better, and create fewer momentum losses, simply because they're new - or that may be a part of it - but 70-88mpg at 70mph is very impressive. Fortunately for me, I am entirely happy to drive slowly most of the time and 50mph is a perfect motorway cruising speed for me. For that reason - and for the reasons of both cost and comfort over speed bumps - I think I won't lower my suspension, but for most people it seems it would make a huge difference to economy. Whatever happened to those Citroën cars with the active suspension that you could lower and raise at will? That would be ideal.

As for the 'gentle-acceleration-vs-brisk-acceleration' question, well yes, I have tested that. I have a 50mph circular route that I use for testing the effect of mods on mpg. It's about 10 miles total: a rolling start at 50mph on a local dual carriageway. I zero the mpg meter as I pass the start location, drive the 5 miles at an indicated 50mph using cruise control, then slow down for the roundabout at the end, stopping for at least one of the three sets of lights on the roundabout, accelerate up to 50mph again for the return leg and maintain that until I pass the start point again, at which point I note the reported mpg average for the circuit. (I use the car's normal mpg display. Not accurate I know, but consistent enough for an A/B, before-and-after test of percentage difference in mpg following a mod. The display will read between 95 and 99.9 mpg these days. Less in winter. (The display seems to be about 6% or 7% over-optimistic overall. On my next really long journey I'm going to check exactly how optimistic it is at 50mph. I suspect it is less optimistic than at slower, city speeds.))

Obviously a significant part of the fuel used in that loop is for accelerating up to 50mph again after stopping, and I have experimented with different accelerating styles, including letting the cruise control get up to its set speed again on its own. My conclusion is that very gentle creeping up of speed is not good because even gentle acceleration uses far more fuel than steady cruising, and creeping up the speed just prolongs the extra fuel use. Aggressive acceleration, or even very positive acceleration (difficult to describe exactly what I mean but I hope you get the gist) is TERRIBLE for fuel economy - the average goes right down and doesn't recover. What works best is fairly gentle but positive acceleration, and getting into top gear as soon as possible consistent with that definite acceleration. In fact, kind of 'normal' acceleration works best. (Think typical minicab driver style?)

At present my engine is in a remapped state - having had it remapped on a 'like-it-or-money-back-and-your-original-map-restored' basis. I did explain that I was interested only in mpg improvements. Disappointingly, it has increased my fuel consumption slightly. Slightly but definitely. Even on a steady 50mph or 55mph route on a flat road, the fuel consumption is significantly up, and overall, tank-to-tank consumption is up by a good few mpg. A shame. I had put a lot of hope in getting a remap. The car drives better of course - much more torque, to the point where 5th gear feels like 4th gear used to feel - but for me that doesn't help much and actually makes it harder to drive economically. I will get it put back to standard as soon as I can arrange it.

Just to be clear, did you change your gear oil? If not, I can highly recommend it. A bit unscientific in that I put the Molyslip in at the same time as renewing the ten-year-old gear oil, but wow, what a difference it made!

Thanks for the tips!

The scangauge is very handy in many ways, not only for fuel monitoring. As you asked, my temperature never gets above 74 degC, except in summer in stalled traffic. I think it got to around 85 degC on one occasion. If this is correct, a grill block would be very handy indeed.

Another good use for the scangauge is the throttle position sensor. Except in rare situations, like overtaking or up hills for example, I never go above 65% of my throttle. This is one of the reasons I attain high MPG at speed. Another is that I follow other traffic, however fast they are going. In a former life I used to be a competitive cyclist and one of the things you learn is that by tailing another rider you can conserve 30% of your energy by letting them push through the air while you follow in the slipstream.

I haven't yet changed my gear oil but based on your experience I will request it next service in November. I'm looking forward to see any results and as it will be up on the ramp anyway it should prove to be minimal cost too. Thanks for the heads up on that.

I'm going to have to find another set of those lower grills to cover up and replace the ones I have. Air in the wheel wells is a major source of front-end drag, so short of cutting exit vents in the bodywork it's best not to let it in to begin with – or as little as possible. I'm also trying to find a suitable flexible material for a front air dam. Being such a low car, any extension below the bodyline is going to be tested to destruction on our roads!

So if your thermostat is working, your radiator is not being used at all, ...ever! You could remove the radiator and the fan to save weight! Ha ha.

The themostat should only begin to open at 87 degrees and should maintain a temperature of about 92, using the radiator to regulate things. (Anything up to about 105 is absolutely fine and normal. The dash guage will show '90' between 75 and about 107 I believe. The radiator fan cuts in at a certain temperature... About 102 perhaps? I forget.) When I changed my thermostat last year I tested both the old one and the new one with a pan of hot water and a thermometer. The old one was beginning to open at 65 degrees (!) and the new one at spot-on 87 degrees.

Once I'd changed the thermostat, things warmed up very appreciably, and I did see a rise in fuel economy (it was November I believe) but looking at the actual coolant temperature via VagCom, it still wasn't getting up to temperature, and the thermostat was never opening and never sending heat to the radiator. So I started gradually blocking the radiator grille, monitoring the temperature at every stage, until it was 100% blocked and all was well.

One other thing I notice with the grille blocked is that the engine loses much less heat when parked up for an hour or two. If I go somewhere in winter and park the car for an hour or so, when I come to drive it away the engine is still pretty much up to normal temperature. Well, 75 degrees at least, as the temperature needle shoots straight up to '90' on the gauge and the heater works straight away.

I've been thinking of ways of improving fuel economy in winter. Been looking at small 240v self-adhesive pad pre-heaters on oil sump and gearbox for early morning starts.

Many people have used garden liner.
Cheap and fairly sturdy.
You'll grind it down to where it needs to be. :D

Lower (cold) weight oil definitely helps in the first miles.
Engine uses notably less fuel and is less noisy.

Once warm, the effects are small though, so the effect on your overall FC depends on the length of the average drive.

Thanks Euromodder. In winter most of my journies are short, local, work-related ones.

Using cheap mains electricty to warm the engine up rather than using expensive diesel to do that job makes sense to me. I also notice that on a long journey, the mpg goes up and is at its maximum after about two hours' cruising. I'm guessing this is not engine-related (the engine should be pretty-much heat-soaked after half an hour?) but related to other parts of the drivechain warming up, e.g. the gearbox, axles, CV joints, wheel bearings, tyres, etc. Hence wanting a heater on the gearbox as well.

Ultimately it would be very cool to use solar-charged auxilliary battery power to run the heaters. They could be on a timer to come on a couple of hours before drive-time.

Ultimately, ultimately, it would be super-cool to use that auxilliary battery (charged either by solar or by mains) to also replace or supplement the alternator. I.e. to use the aux battery to run a voltage-regulated 'charger' for the main battery so that the alternator 'sees' a high voltage most of the time and doesn't bother generating amps. For daily short journies, or for longer trips with lots of rest time, the solar regeneration might be enough, and when it isn't, the car can be plugged into the mains to top up the aux battery. And with that kind of arrangement, even if the solar isn't enough, or the mains charge doesn't completely negate the need for alternator charging on longer journies, any solar/mains power you can put in WILL save you a corresponding amount of fuel. Mild hybridisation.

That all would need a bit of electrical/electronic design/calculation, plus some investment of course. I think it should be feasible but first I'll try with a couple of pad heaters. (Maybe 12 volt ones so they can be used in any future solar/aux battery arrangement.)

Sorry - thinking aloud, ...kind of. I've been thinking about this over the last couple of days. My feeling is it would work. Probably cost-neutral at best, but you get the added benefit of quicker, more comfortable winter morning starts where the cabin heater kicks in much sooner.