What can cause a significant drop in fuel mileage in a car?

Question

My Subaru dealer would not probe into this matter without a check engine code and suggested that it is the "winter mix" in fuels that is most likely to blame. However, I find it hard to believe that it would account for a drop of about 7-8 mpg.

The car also is less repsonsive to the gas pedal. There is a hesitation before the automatic transmission downshifts.

Answer 1

Sounds like it may be the engine temp sensor that the ECU uses, not the one for the temp Guage. This will cause the ECU to send more gas to the cylinders as it thinks the engine is cold.

Go to this site and post your question there. You'll have to sign up, but you can get just about every question answered. Lots of knowledgeable Subie owners.

http://www.ultimatesubaru.org/forum/forumdisplay.php?f=3

Good Luck

Answer 2

During the winter you probably will get lower mileage, due to the longer amount of time for the engine to warm up, increased drag on other parts until all the fluids warm up.
A drop of 7-8 does sound a little strong even for winter. That is about the difference between city and highway driving. Have you changed your driving habits lately? One last thought, could someone be siphoning fuel from your car?

Answer 3

I would agree with the check engine code part of his diagnosis. There are so many issues that could cause problems. 1st thing to check is the air filter, spark plugs and wires, but an oxygen sensor, misadjusted timing, a slipped timing belt, valves that have slipped out of adjustment, or so many other problems could be at fault. I would recommend doing a complete tune-up, including plugs, cap, rotor if it has one, wires, and air filter along with checking for obstructions in the air intake system and also checking your caralytic convertor. If that doesn't work, then move on to the check engine codes.

Answer 4

check to see if your converter is plugged up (restricted exhaust will drop mileage) as well as a bad oxygen sensor can do the same thing . change your fuel filter, air filter and plugs,check your engine timing and change your trans fluid and filter (with fresh fluid and filter it will shift more efficiently and save you money later).Your check engine light should come on when you turn the key to on (if you do not see it come on briefly and go out it may be burned out),but
if you live near to an AUTOZONE PARTS STORE you can get them to code read your car and tell you the trouble codes in writting .

Answer 5

gasoline economic device is ninety 5% driving force, 5% vehicle. What replaced approximately your using behavior? additionally, to be precise gasoline economic device desires to be averaged out over long classes of time, not by way of the 0.5-tank.

Answer 6

ask him to check because you think the check engine light bulb is out, otherwise tune the beast up and see if that changes matters

Answer 7

needs a tune-up and change the air filter and fuel filter.