My 1999 Elantra with 133,000 miles gets around 30 to 31 mpg with country roads and so forth. In the winter, that goes down to 27-28 mpg. Maybe the winter additives in Pennsylvania. This is probably right with the specs for this car. But others have gotten more, around 33-34 mpg. I wonder. The first 76,000 of the Elantra's life was spent in the big city with the transmission in power mode. So lots of stop and go city driving puts the car under load. When I got it at 76,000 miles, I changed to Economy mode for the transmission and mostly country driving. How to tell if the cylinders and rings are maybe a little worn. The dealer has a diagnostic tester. Would it be this sensitive? Most of the sensors have not been replaced. Just the upstream O2 sensor. I have a downstream O2 sensor and a transmission speed sensor sitting around waiting for replacement. I thought, maybe the MAP sensor. Or maybe I am replacing things and don't really know what I am doing without some kind of real-world diagnostics? One place, Pep Boys, wanted to sell me a fuel treatment job for $250 but why bother unless a specific thing is wrong? Again, driving in the dark. I'll just put in Lucas fuel treatment in the gas tank for $4 instead. I did change plugs and air filter and that counts. Any ideas? Trying to prioritize. I think a ball joint and the timing belt are probably higher priorities over the gas mileage. If I lose the engine, nothing else matters...

 

MPG always goes down in the winter. Winter fuel is one reason, the cold air is another. Extended idling to warm up the car, etc. I don't think you mileage is unusual.

 

I can't idle this car. Believe it or not, I read the manual - must have been bored - and the manual said not to idle the car more than three minutes. What? Hard to believe but the 2 liter DOHC engine does run hot itself but the dash gauge shows less than the midpoint for hotness. But three minutes? Still cannot believe that. I'm almost sorry I read the manual in winter. Ignorance truly is bliss.

In any case, the weather has been very mild the last few weeks here, so it's either the fuel or maybe a small vacuum leak confusing the car computer. There is a pinhole leak at the flex pipe leading to the cat converter. That might do it?

Thanks for replying.

 

The 99 that I had had the same mgp as yours does. It's normal. I always felt that with the size and shape of the car it should do better, but it didn't.

Only the newer Elantras get that 34 mpg. My 09 gets it. I don't know if they changed the way the engine operates or if they just lowered the weight of the car.

 

They're using aluminum I think (read it somewhere on hyundaiusa.com while I was researching which car to buy). Lower fuel efficiency can also be a fuel pump that is starting to go (that happened to my bimmer and after the fuel pump failed and was replaced, the fuel efficiency went back up by 2 mpg better). I know this is a Hyundai forum, but I'm thinking most cars are fairly similar. Not sure if there is a way to diagnose this without the part failing first though.

Maybe also fuel filter (if not done around 100k miles).