[paulgato]

I read your thread with interest. I have a 2002 Mk4 Golf estate I've modded a bit for mpg here in the UK. Mine is a 1.9 TDi diesel. I wan't quite sure but it seems yours is probably a petrol (gas) engine...?

Still, the basic car will have some similarities, diesel or not.

I think you're entirely right to prioritise simply making sure all mechanical faults are corrected. After I bought the vehicle I found significant mpg gains from changing a thermostat, changing an alternator, replacing worn suspension bushes, getting wheels accurately aligned (zero toe-in works well and is actually what VW specify), changing a temperature sensor, and renewing the manual transmission oil.

(The alternator was replaced because it failed, but also it turned out had a stuck freewheel pulley. The new alternator had an operating (freewheeling) pulley which suddenly enabled the car to run smoothly at idle speed (800rpm) enabling me to drive in 5th gear at 27mph or 4th gear at 20mph, thus boosting my in-town mpg enormously!)

(VW say you never need to renew the gear (transmission) oil but after 150,000 miles I changed it, added a small tube of Molyslip, and I could feel the difference instantly. Probably gained 2 mpg from that.)

So yes, step one is to make sure the car is running as designed.

Next simple mod is tyre pressure. I just pumped them up to the max sidewall pressure marked on the tyres, which was 51psi. I found it drove WAY better like that - didn't wallow through corners any more - and mpg was significantly up. It makes hitting potholes a bit alarming, but I drive so slowly that I can generally avoid them. I've run tyres through their entire life like that and there's no (zero) signs of uneven tyre wear. I think that thing of tyres wearing excessively down the centre line when over-inflated only applied to older, non-steel-belted tyres.

I always meant to do some aero mods, although I am uncomfortable about anything which draws attention, so I've kept both wing mirrors and wouldn't contemplate a boat tail, etc. I have a (stock) under-engine tray, and always intended (still might) to fit a rear undertray, mostly to cover that horrible scoop-shaped gap just between the rear bumper (fender) and the spare wheel well.

What I have done is to fit an engine pre-heater and an extra battery and charger, etc, so I normally don't use the alternator, and always start my journey with a 70% warmed-up engine. That 'plug-in mod' saves me about 15% on fuel overall, but it wasn't easy or cheap, and it does shorten the life of batteries to have them discharging daily like that, so I don't know if I can really recommend it, but I have no regrets myself.

I did remove the A/C compressor, a) because I never used it and it is surprisingly heavy, and b) because I had to mess about with the alternator a lot to get it to work and I got fed of struggling with the serpentine belt all the time. I dumped the A/C compressor and got a belt for the version of the car with no A/C. Whew!

This probably only applies to the VW diesel engines, but they overcool massively, and even in the mild English climate absolutely REQUIRE an aggressive grille block if they are to run at the designed temperature over the winter. You will have discovered with your Torque app that the dash temperature needle bears little relation to the actual temperature. Mine is designed to show exactly 90 degrees C (dead centre) at any temp between 75 and 107 C.

As for driving style, I've found that the Golf is relatively heavy and needs to be driven 'like a boat' for maximum mpg. I.e. assume you have no brakes. Pick a speed that you can maintain safely both on the straights and on the bends and stick to it.

Hope you don't mind the unasked-for advice. Take from it what helps and ignore the rest.

I've kind of lost interest in eco-modding as such. It's been an interesting exercise. I had wanted to get up to 100mpg (Imperial) but never managed it. My best ever was a measured 89.9mpg average on one tank of fuel over about 1400 miles. (As per fuelly.com stats) I could certainly get well over 100mpg on a long slow run in good conditions, but not in 'real world' driving over a tank-full. I came to the conclusion that the main obstacles to fuel efficiency are political rather than technical, so I joined the Green Party and stood for office last May. Didn't get elected. Will try again this May, as local govt re-organisation means we have elections again this year.

I reckon that if maximum speed limits were reduced to 50mph and it was known that they would never rise again then manufacturers would design for that speed. Smaller, lighter cars and engines small enough to be running at about 70% load at 50mph would become the norm. Cheap and simple electric cars would suddenly become much more viable if highway speeds were reduced to 50mph, etc. etc. Cycling would be safer if cars were smaller and slower, so more people would leave the car at home more often and cycle. Other advantages: wildlife would be squashed less with cars going at 50mph. (Wild animals have evolved to cope with things moving at around that speed, but often get confused with traffic moving at 60 or 70, especially at night.) Oh, and aquaplaning is physically impossible below 50mph even with completely bald tyres. That one simple (political) change in maximum speed limit could, I reckon, cut overall vehicle emissions by 50% after ten years.

Anyways, good luck with it all.