I own an '03 Elantra gls.. and I've been getting poor gas mileage for the past while. I filled my tank a few days ago.. I've only driven about 50 miles, and already I'm down a quarter of a tank. Any ideas as to what's goin' on??

 

From least to greatest check on the following: Oil, fuel filter, spark plugs & wires (distributor cap/rotor), O2 sensors, muffler, & timing belt. I say if you change the first 3 and still are having problems then maybe take it in to check diagnostics.

 

Hi to Jlivan. I own a 1994 1.8litre Lantra which is the ame as the Elantra and it does not have a distributor. It has a coil pack controled by the computer. I think this setup is standard. Did Hyundai change back to distributors in the later models?

 

bad oxygen sensor will cause poor gas mileage

 

I don't want to scare you, but it wouldn't be the first time, that a tank has shrunken to half size. A friend of mine had this problem with his Opel Corsa and it must be an issue every now and then with many brands. Not only Hyundai.

 

Definitely oxygen sensor or plugs and wires. My mechanic said it is very rare for a fuel filter to go bad. I changed my Ox sensor at 80,000 miles, big difference, changed plugs and wires twice, big improvement.