big change in driving distances and change in MPG?

OldSchool

A2OC Donor
i used to drive at least an hour each way on empty country road at night to work (fast and rarely stopping) a day and 1 to 3 times a week 4 hour motorway trips twice a day and was getting 65 to 71 mpg

i moved house and changed jobs and now drive about 2 minutes each way 1 or 2 times a week for groceries (i walk to work now) and every 2 weekend a month a drive 30 minutes on empty country roads and my mpg has dropped to about 50mpg

i do have maybe 2 tires with slow air leaks and now that i don't drive as much i am not as diligent in putting air in tires as i used to be.

so maybe there are more than one factor at play here?

does this change seem normal-ish?

i reckon the engine rarely gets to the normal operating temperature...

there is a store I like better about 30 minutes away so that could easily replace my shopping destination 2 minutes away if that will improve things... or would it be a false economy?
 
You need to get a Petrol car. This is the same problem I have in my 535d, it’ll do 45mpg on a run but it’s mainly used around town and does 32mpg.
 
I think you've put your finger on the problem. Engine isn't getting up to temp, so is running rich most of the time. The mpg figures you quote sound about right to me.

This is probably less of a problem with a diesel, because the excess fuel doesn't wash the oil off the cylinder walls like petrol does, but it won't be good for the car, longer term. I'd suggest finding an excuse for a longer, faster run at least once a week. Won't help economy, but will help engine life, I suspect.
 
I can confirm that when the car is not up to normal running temperature (90 Deg C) the ECU will inject more fuel
There are a total of 8 fuelling maps which the ECU uses depending on engine coolant temperature.
There is also a common fault in that the engine temp sensor is prone to going faulty and because it as two separate circuits one feeding the gauge and the other the ECU is can 'appear' to be OK as the gauge is moving to 90Deg C, but the ECU could be seeing something totally different and therefore applying the wrong fuelling map
This can be checked using VAGCOM / VCDS / VW Tools, but if this is not available then changing the sensor is not expensive and a fairly easy job
If the car is not getting to temp then the thermostat is the likely culprit, again not expensive, indeed I changed both of these yesterday on 'Cloth Ears' A2 along with a remap, all done in a few hours

The remap will yield on average about 5 mpg extra if you don't use the extra power available
cheers,
 
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