No Check Engine Light but Gas Mileage is getting shady.?

If you have switched jobs or moved, and your new commute is much shorter than your old one, or takes more city driving where your old job was a highway commute, could easily account for a drop in MPG. Also, if you have moved to a colder climate or a mountainous region from flatlands, you could easily see such MPG drops.

If none of the above, then it could be maintenance items mentioned by others.

BTW, your belt probably has nothing to do with your drop in MPG...but...I would suggest getting it changed soon. 8-9 years is a long time. If it goes, your engine will be toast.

I would suspect the O2 sensor. If you did a complete tune up (wires, plugs, rotor, cap) and didn't do the O2 sensor, it could be the cause. O2 sensors will still work even when they begin to fail, but what I've seen happen, is they will start making the engine run rich (high fuel content to air ratio) and thus plug/melt the catalyst in the converter. THIS could be the problem, but I would first replace the O2 sensor or sensors if yours has a before converter and after converter.

One free way to check this, is to undo the negative side connection of your battery for a few minutes. Once you connect it back, start the car and let the computer "relearn" the engine settings from the sensors. If you have a failed sensor, maybe it will throw a CEL, maybe it won't.

BUT, what this will do, I speak from experience...what this will do is equalize everything that the computer may have been compensating for or overadjusting for a failing sensor of some sort.

Just my two-cents.....

many items can explain lower fuel mileage, such as injector spray pattern, thermostat not reaching correct temp for ecm to lean out fuel mixture, we have installed thermostats that have increased mileage by 15%, low compression, 02 sensor ,bad air filter , bad fuel filter, catalytic converter restriction, tune-up related issues, tires low on pressure and there are more but you get the idea..if you were my customer i would replace the thermostat, many mechanics, say it wont make any diff. well they are wrong if your car is running 20 degrees colder than normal your fuel consumption will raise at least 10% and will be running rich,( and the gage on the dash will look basically the same ) the ecm does not know weather your car is just starting out or has been running all day... when it goes into closed loop it takes a reading and sets the fuel strategy..hope this helps

I believe that everything on your car is fine but the reason for lower mileage is due to the gas your getting.In winter they put more methanol into the fuel for winter use when they make gas.There isn't a thing you can do about it because its the only way it comes on the trucks when they deliver it to gas stations.But if you think your getting water in the gas go to a pharmacy store and get a few bottles of rubbing alcohol with a 92% on the bottle and dump that in along with some gas treatment.It doesn't make any differences which gas treatment you use they are all the same.hgm20002000@yahoo.com

The biggest thing that kills mileage that much in an older car is a clogged cat. A muffler shop can tell in ten minutes by checking the pressure before and after the converter.

Check your compression.

NOOO!!!!!!!

Don't change or flush the tranny!!

It will never work right ever again.

Nothing ever keeps getting the same gas mileage.

Engine wear, hell....everthing wear.