Sudden MPG drop

My 2000 corolla has consistently gotten35 MPG until last month, suddenly I’ve dropped to 18-20 miles per gallon, a friend suggested fuel filter fail, but i can’t discern if it has an external one

Earlier then 2001 may be at the fuel tank. I would encourage that to be done by a mechanic at a garage if it is. It may need a tune up in general including air filter and inspection of vacuum lines, dragging brakes etc. which I would suspect too. When was that last done ?

It certainly does have an external fuel filter but I’d be more inclined to look for a faulty O2 sensor first.

I Believe That If A “Fuel Filter Fail” Caused That Kind Of Decrease In MPG That You’d Smell Gasoline And You’d Be Slipping And Falling In The Stuff.

Has the sudden drop in mpg been accompanied by any performance issues (rough running, idling, stalling, stumbling/missing, smoke, etcetera) or has the “Check Engine Light” illuminated ?

What procedure do you employ to check your mpg ? Is that an average over several fill-ups ?


amazed and grateful at getting a response so quickly, I reset my trip-ometer and rarely do I not fill-er up so its very easy to keep track of mileage, I haven’t noticed any other problems associated w/ this sudden drop. I’ve had the car 10 years and am always pleased to see what great mileage and overall good performance

In addition to the other suggestions, you might also have a bad MAP sensor or ECT sensor. Those two sensors also have an effect on fuel economy.

Hence the word may and if…wasn’t sure…notice " at "not in .

Add a stuck thermostat to the list of suspects.

thanks, I heard just a snippet about that on a recent episode

check you air filter

The guv’ment sez air filters have little effect on MPG:

How many miles does the car have on it?
When was the last time you had the sparkplugs changed? What brand did you use?
Have there been any other operating problems?

If you plan to work on the car yourself, a repair manual will be invaluable. They’re availebl over the internet or at your local parts store.