Reduced MPG?


Registered User
Hi All,

First time poster

I recently bought a 2002 A4 Avant 1.9tdi sport 130bhp. The Thermostat was faulty and the temperature gauge did not rise any further than 55 degrees. I was only averaging 40mpg, with 90% motorway driving. I was disappointed with this, so I replaced the thermostat. The temperature gauge now reaches 90 degrees when warm as I would have expected. However, It can fluctuate slightly from between 75-90 degrees even after a long period of time when warm, particularly if driving at slower speeds or stop/start driving like in the town. Is this normal? I was under the impression that with audi's/VW's once the temp reaches 90 degrees it stays there regardless.

My MPG has also improved from 40mpg to 48mpg. I would still like this to improve as I do mostly motorway driving. Any Suggestions?


Registered User
I would check the actual temp sensor as well. If you do have to replace it use a genuine one.


different gear


Registered User
I should have mentioned, I have already also changed the coolant temperature sensor. I am very particular with regards how I drive to maximise fuel economy, ie no harsh acceleration/braking/gear change/ and I sit at 60 on motorway etc
Might the fuel temp sensor affect the fuel consumption? Anything else?
What else may be causing the fluctuation in the temp garage?


Registered User
I've averaged 36-45mpg so far from my unmodified FWD 1.9TDi Avant. I think I'll get my thermostat and temp coolant sensor changed to see what happens. I to have been trying to maximise my mpg through my driving style. From what I've read on forums, I was expecting at least high 40's all day long!


Well-Known Member
VCDS Map User
I have to ask. Were the thermostat and temp sensor genuine? Because I bought aftermarket and soon had to buy genuine.


Registered User
Both parts were aftermarket. Temp sensor was off ebay and thermostat was from eurocarparts. Foolish?