'04 Elantra Won't Stay Heated
 

So I just purchased a used '04 Elantra with 73k miles the other day and it test drove very well. Today I was driving on the interstate and realized that the car just would not heat up when the dreaded check engine light illuminated. I took the car to AutoZone and put in some more antifreeze and noticed that the car would warm up when I would idle or drive fairly slowly but then cool down rather quickly when I sped up. I think something just isn't holding its heat. Any suggestions?

RE: '04 Elantra Won't Stay Heated
 

Where did you put the antifreeze in? In the reseviour on the side, or the radiator itself? It takes a while to work the air out if it was low.

Depending on where you live, it has been extreemly cold. Put a piece of cardboard in front of the radiator while it's really cold like this. You can cover most of it, it will be ok and not overheat as long as it's got antifreeze.

RE: '04 Elantra Won't Stay Heated
 

I put the antifreeze in the reservoir last night and nothing has really happened today. I spent about 90 minutes driving around town and there's still a lot of luke-warm air coming through and a nice bright "check engine" light. Ihave also noticed that the temperature needle doesn'tbudge at all. It has been pretty cold here in Indianapolis, but it's not cold enough for me to think cardboard to be necessary. My girlfriend's Yaris is holding up just fine in his weather. I'm wondering if I have a dead heater core or a busted temperature sensor.

RE: '04 Elantra Won't Stay Heated
 

Ok, well go get your check engine light checked. Go back to Autozone and ask for a free code scan, write them down, and tell us what they are. If your not getting heat, and you know you have antifreeze, then cardboard is a wonderful idea to get heat. It's not the heater core or a temp sensor. It could be a thermostat that's stuck open.

RE: '04 Elantra Won't Stay Heated
 

I suspect this is the problem, but check the coolant level through the radiator neck first. This is aa easy and relative cheap problem to solve.

RE: '04 Elantra Won't Stay Heated
 

I'm quite glad I posted on this forum as these responses are really reassuring! I was planning on taking the car in this weekend to get it looked over anyway, so I'll let everyone know the results probably by Monday. Thanks!