[euromodder]

Originally Posted by 1.9SDI

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.

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

I've already ordered a suspension lowering kit

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).

I've also bought some cheap used alloy wheels from an Audi A3 and increased pressures to 45PSI.

Light wheels with small openings are a bonus.

Planned mods after fitting the suspension upgrade is to convert to 100% biodiesel, saving me at least 25% on fuel costs.

And burning a renewable fuel.

maybe reduce the width of the tyres from 195mm to 165mm.

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.

I'd really like to know how to ease the airflow over the wipers, if anyone knows?

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.

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?

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

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?

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

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)?

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.

Are there any other mods that are proven to be cost effective?

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.