Low Mileage on Elantra

I have 2004 Elantra(GLS) with 145,000+ miles. Recently my milage dropped from 30+ to about 20. What could have gone wrong?

That’s a huge drop…Could be winter gas formula.

How are you calculating your gas mileage???

Yes, it could be the winter gas formula.
Or, it could be due to excessive warm-up time.
Or, it could be the result of using drive-up windows at banks and fast food joints.
Or, it could be the result of a cooling system thermostat that is stuck in the open position.
Or, it could just be a case of the “chickens coming home to roost” as a result of lax maintenance.
Or, it could be the result of tires that have lost pressure because of the lower ambient temperatures.

Or…it could be the result of all of the above.

OP–What can you tell us specifically about this car’s maintenance over the past 3 years?
Please give us actual maintenance details, rather than a meaningless phrase such as, “it has been well-maintained”.

Also, if you would, let us know what the weather has been like lately where you live.
Where I live it’s recently dropped to the teens in the evenings. @#&%* cold. That could easily account for 3 or 4 mpg. Any or all of the items listed in VDC’s post could account for the rest.

Oh, and are there any other symptoms? Any repairs lately?

…and…is the Check Engine Light illuminated?

Whenever my friends turn to me personally for problems with low mpg, I at least have a chance to probe a bit. Typically, 9 out 10 times, the answer lies in the data. That is, their method of determining mpg is most unscientific.

Too often it is based on figures for a single tank of gas; or even less than that. Or estimated by the markings on the fuel gauge. Or there is a simple calculation error.

This question frequently arises here and we are never given data. And so we trudge through the usual list: weather, ethanol, tire pressure, and so forth. And so… naw, I’m just going to drop out here. I’ve nothing more to say. Carry on.