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Hi folks, this is gonna be a long post, but please read if you know anything about Polo GT fuelling problems.

Right, background. About 2 years ago my car started running peculiarly. Idle was unstable and I was losing power until the car had reached running temperature. I took my car to my regular mechanic, to VW and to another specialist. None of these people had the foggiest idea what was causing the problem.

Since this, a number of attempts have been made to make my car run correctly and the following have been replaced:

- Blue temp sensor (twice)
- Black temp sensor
- Distributor (old one had a bent rotor)
- Lambda probe
- Air Flow Meter (for a Golf item with K&N - which had no adverse effects on running)

None of these solved the problem, however, the car was running considerably better despite a little juddering. About a year ago, the fuel consumption of my car went up dramatically with no change in weather/driving style. A little over 250 miles to a full tank most of the time. So I posted about this on Porka and on here, and an idea came up to improve the earth for the lambda probe. Having done so, fuel consumption returned to normal.

Last August, my head gasket was changed. Since then fuel consumption has steadily returned to the crappy 250 miles to a full tank routine. My bodged earth was still there - so I'm confused as to what's wrong with it. Only change while driving is more of a tendency to heat up especially in heavy traffic. The temp guage was showing a reading close to the top of the scale instead of the usual reading of being halfway between the top and bottom of the scale. Sometimes, also in heavy traffic, the red light on the instrument panel lights up despite a normal coolant level and coolant temperature.

I am assuming that this red light has something to do with the non-vag coolant tank I bought last year which is obviously telling the ECU that there's not enough coolant in the coolant tank when there is plenty. Could this affect fuel consumption? When plugged into an ECU fault reader it also sometimes (not always) reports a fault with the lamda - but I don't want to replace this unless I'm sure it's the problem. £60 is a lot to shell out if it doesn't sort anything.

It's definately overfuelling, I can smell it.

Please, if anyone has any ideas as to what could be wrong could they post them up here. It's running fine 95% of the time at the moment, even when cold, so I don't understand the heavy consumption. I can't afford to spend all this cash on petrol, so my student railcard is gonna be getting lots of use if I can't sort this out.

Alex

I would recomment changing the thermostat if the temperature is high. Get a genuine vag one, about 11 quid plus the seal. Does the header tank have the level sensor ?

Despite that, it sounds like your lambda probe might be duff. The cheapest place for the genuine bosch item is GSF, unless you want to try a second hand one. I have a spare one here you can try.

Don't know whether it has a level sensor, but my old one did. Since the head gasket was changed it's never run low on coolant.

Does the thermostat affect fuelling?

The lambda probe keeps coming up as a suggestion, so I'm thinking carefully about changing that.

The thermostat could possibly affect fuelling slightly, i.e taking longer to warm up.
It doesnt sound like its the main fault though, from what you describe it sounds like the lambda causing the overfuelling.

Just out of interest, have you had any non-genuine temp sensors (blue or black) fitted ?

Both of my coolant temp sensors are genuine items from VW, as advised by my mechanic.

Mark Hunter's posted some engine efficiency stuff on the Club Polo e-group which I'll give a go next week. If all else fails though I may have to change my lambda costly.