2005 Neon

When I put the heater on the windows fog up. Mostly not super bad. I believe it has to be the heater core, which I do not want to change. It is not terribly bad and I can funtion the car as it is. Sometimes with the heat on wide open it clears itself up after a while.

My question is what do you guys, and girls, think about using that stop leak stuff for this? And what kinds are the best for the engine. I have used this stuff in the past with no engine problems from it.

Many people have used this successfully for heater core leaks. But do not go crazy and use more than the recommended amount (probably 1/2 bottle for your Neon) or you’ll clog the whole cooling system. Also be sure to flush the system first.

If it smells sweet and leaves an oily film on the inside of the windshied it is a leaking heater core.
If it doesn’t smell sweet you may just have to make sure you heater controls are not set to recirculate.

It could be a clogged ac drain line leaving extra water sitting in the system. Noticing any coolant loss?

I wouldn’t use that anti-clog stuff for fear of damaging the engine cooling system. Think how much a replacement engine would cost if the stuff clogged the radiator and the engine overheated badly. If I couldn’t afford to repair the heater I’d just live with cold temperatures inside the car and wear the appropriate clothing. There are some aftermarket products available that use the battery to provide a little heat to the passenger compartment, maybe use that until you can afford to fix the heater core.

Dear @GeorgeSanJose I was talking about the coolant line that drains water build up from the ac. If it is clogged it can accumulate water, and that becomes part of the problem for many. It is not using an anti clog but clearing the drain, most shops will blow it out for a minimal charge if needed.

I’ve read many times that it’s unhealthy to breathe coolant fumes for very long. If that’s what’s going on here, you’ll want to get that corrected one way or another pretty quickly.

Yes Barky, I’m not disagreeing with what you say abut the AC drain line. I was referring to the OP’s idea that the fog is due to the heater core itself leaking coolant, and using a stop-leak product to plug it up.

I’m curious; why do you not want to change the heater core? It is, after all, the only way to properly fix the problem.

He doesn’t want to replace the heater core because the repair approaches the value of the car. It includes removing the whole dash in many,many steps and evacuating the a/c system, removing the evaporator and recharging the a/c.

I do not want to change the heater core because it is a pain in the blank. Using the air cond. does not cause any fogging. Only when heat is on. It is a sweet smell and sometimes you can taste the antifreeze. But for the most part it is not bad. Mostly once you crank up the heat the window clear up and the smell is gone. I have used the stop leak in other cars with never having any problems. I do not know what the charge is for getting this changed but I do not think it would be approaching the value of the car. I could do it myself, but I do not feel like doing all that.