My ac/heat vents have a fog like coming out of it when I'm driving down the road. the heat and air condition are off but all of a sudden a what looks like fog comes out of the vent. I figured maybe the heater core but it comes and goes. The other day it kept doing it then today it didnt do it at all. I recently replaced the radiator and I flushed the heater core and blew air with my air compressor and water through the heater core and used apple cider vinegar to flush it. I also changed the thermostat to a 195 thermostat. A buddy of mine said that I needed to let the car run for a while with the radiator cap off and let the fluid levels drop a couple times and keep adding coolant. Which I did. He also said that I needed to turn the heat on full blast and let it run also so that it could get the air out. I just tried this tonight. I dont no if it worked or not but I was wondering what u guys think is going on????? thanks?

Do a search in the DIY/FAQ section for "burping coolant system."

When this happened in my truck the heater core was shot.

That was my guess, but having air out of the system needs to be done to properly diagnose problem.

Mine too. Mine was accompanied by an insta-fog on the windshield if the temperature **** was not on cold and I turned the air onto any setting.

yeah my windshield fogs up all the time and the defroster sucks! I'm alwasy wondering why i have to run the defroster constantly.

Mine wouldn't fog until I hit the defroster though. It put a film (coolant spray maybe) on the windshield that I had to scrub off with a dry towel just to be able to see since the air is what caused the fog.

its been real cold here today and snowing, sleeting, raining all day depending on where you are. Its rite arouind 34 degrees so some spots have snow. My house doesnt. But driving around the windshield fogs instantly. If i run the defroster it does nothing. I have to wipe the windshiled and wiping it, it smears all over. It was so bad i almost hit **** a ton of times on the way home because I couldnt see beteween all the smearing, fog on windshiled and peoples head lights.

That's a leaking heater core, guaranteed.

Yup...and burping the system won't help. Now when you get it back together....then we can burp.

I found a simple trick to burping the system. It was a hose clamp on the coolant recovery hose coming from the radiator. I've stoppped using coolant and my heater core doesn't gurgle anymore.