VW Passat temp & fuel question - msm
I have a 99 Passat, 1.8T. A month ago I handed it into a VW garage for a service and since then my fuel consumption has dropped from about 28mpg, pre service, to 22mpg now. Nothing has changed to warrant such a decline in mpg. VW says there is no reported fault so there's not a lot they can do. Somehow I found that reply less than satisfactory, rightly or otherwise.

I used to have a 3 litre Omega which done me 20mpg and so the Passat's 22mpg is totally not on.

The other problem I've had for a long time now is the temp gauge is irratic. I posted here before and it was suggested the temp sender unit may be faulty. Again, VW have checked the car out and say everything is ok. Temp sender is fine, so the problem is a mystery.

I also had a leaking heater matrix which I had replaced and for about a week the temp needle behaved itself, but soon after it went back to jumping between zero and half.

I'm stumped! Got no idea what to do about either problem suffice to say the fuel economy is upsetting and the temp needle problem is an annoyance. Can anyone make some suggestions as to why the fuel eco or temp gauge are the way they are; since VW can't answer the question. Maybe I can get some ideas and go back to them or some other garage and have then check out a few things.

Any advice would be appreciated. Thx.

VW Passat temp & fuel question - Peter D
Logically if the temp gauge goes to zero ( faulty sensor ) then the choke, i.e. longer injection pulses will be initiated perhaps causing the load of fuel you are burning. If this sensor is faulty but not open circuit or outside its limits it will not report an error in the ECU. This may be a corroded connector at the sensor or a high resistance sensor. Some of these units have two thermistors oone for the gauge and one for the ECU but if I recall the passat has a single thermistor unit thus the gauge and the choke may well be related. Is your feul gauge steady. Your para four may be explained by the cable harness being moved when the matrix was changed. That suggests a connector, possible but with no fault I am leaning towards a sensor. Get one from a scrap Passat and try it. Good Luck I hope that helps you out. Regards Peter
VW Passat temp & fuel question - msm
Thx Peter. I thought may there be a connection between the temp gauge and the fuel eco, exactly like you said.

Now, this has all come about after VW serviced the car but since they are saying that nothing's wrong, do I have any recourse? I'm not happy with their work and maybe it's not their fault but since they worked on the car I feel compelled to lay the blame on them.

VW Passat temp & fuel question - 659FBE
The link as I see it between higher fuel consumption and an erratic temperature gauge is the engine coolant thermostat. If this is causing the engine to run too cool, a definite increase in consumption will be the result. I believe VW have had problems with thermostats in some models, possibly as a result of their "get it cheaper from Eastern Europe" policy.


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