My car seems to get great gas mileage (~31mpg on highway) right after an oil and filter change. Then, a couple thousand miles later, the gas mileage drops by 3 or 4 miles per gallon. If I get the oil changed again, the mileage goes back up above 30mpg again. I have noticed this happen for about 4 cycles so far. I use castrol syntec with a mobile 1 filter every time.

Does anyone else have any ideas on what the problem is?

2003 Audi A4 Avant Quattro 1.8T Manual

 

I think it's just coincidence. There's no good reason for synthetic oil to impact the gas mileage by -10% after only 2000 miles. I am curious if all your driving is identical -- all highway or a close mix? Do you change your own oil -- is it possible the dealer/shop is doing something else of which you are not aware?

 

It's definitely not a coincidence. I perform the gas mileage test in the same stretch of highway at the same speed with the cries control. Also, this cycle has gone through 4 times...

 

mabye check your fuel system? if theres noise under your car towards the back you might just need a new fuel filter if its clogged up a bit tht could be impacting mpgs a bit. just throwing this out there

 

I think your reading too much into your gas mileage.... It is not a exact number to begin with. It is an esitmated value.

 

Thanks for the suggestion Vezon. I'll check it out.

Audi Tek, thanks for the input. Perhaps I am reading into it too much, but it's my opinion that car owners should keep a closer eye on these things like gas mileage. Issues like this can be evident of other problems that need to be addressed - a fuel filter for example...

 

Your absolutely right..... Owners need to stay on top of the care for the cars. Its the only way to make them last. Technicians aren't going to come to your house and inspect your car for you.