Hey guys,

As the weather started to get colder I found myself having to use my heater for the first time this season. Well went to turn it on Saturday evening and poof...cold air....ok so let me drive around so the car can warm up. Well about 15 min. later (the temp gauge was in the middle between C and H), the heater was still blowing cool air....

I pulled into a lot and noticed when I revved past 1500 RPM the air would warm up (hotter air would come into the cabin). However under idle or at a light...it would cool back down and blow the same damn air. So i put it on full blast on 90....same old cold air and when I'd rev to 1500+...HOT air.

The only things I have modded recently is my dash, I took apart my dash to complete the Digital Wheelz screen and a DVD player in the upper glove box. I also noticed my coolant level (checked while the engine was warm) in the overflow tank was empty. I figured this might be my first bet, so I filled her up to MAX and warm air began blowing. Again this morning I noticed the same problem and after checking coolant level it was still at MAX. Is it possible since the level originally was empty that I could have introduced some AIR into the system (hence why its not warm air coming in)?? When I swapped my radiator hoses for my SAMCO hoses last year, I had to bleed the cooling system since your introducing air into the system and was having the same problem with the heat. I am just asking b/c I wanted to know if anything I may have taken off or removed on purpose or on accident behind the dash that could cause this problem?? I am also reading that I could have a problem with the heater core valve being clogged?? Does anybody know where this valve is located (should be by the firewall or behind dash)?? Or should I aim straight for the engine bay?!?! HEELLP!! Want to try and avoid the stealership for now, but that will be my last resort. I have an 04 5AT G35c.

 

Make sure there are no lines pinched or anything. Maybe the coolent isnt getting through because the line is pinched.

 

Def. strange though. I've never heard of that problem. that or maybe a sensor? hmm this should be interesting to find out..

 

From your description of increased air temp under high rev's I would speculate that you have a restriction in the coolant line that allows some flow under higher rpm's but not under low rpm's.. The water pump reving higher forcing more coolant thru to the cabin.. Possibly, you may need to make sure no bubbles in the coolant system.. Like bleed it..

 

Did you mess with the white ac amp box behind the ac control piece??

 

Did you vent the heater coolant lines? I believe there is a valve at the high point on the heater hose. There is something in the FSM about air-bound coolant lines and heater efficiency.

 

Hmm, is this the small box thats held in by 5-6 golden screws?? The only white box I recall opening on the AC control piece was the top portion which are the buttons for the AC/HEATER controller. I simply unscrewed this piece, then realized it will not come off, and screwed it back on.

I went out earlier, opened the heater bleeder valve and more air bubbles were coming through. The air seemed warmer from the vents after I let it bleed. I also revved to about 3k RPM as instructed and held it and released. Air seemed warmer, but it usually does and then slowly cools off. Will try heater again and keep everyone posted.

Is it possible that since installing my Samco hoses (around March/April) I may have NOT completely purged the system of air bubbles?? I dont think I have used the heater since then, as the weather began warming thereafter. However I do recall my heater then was having the same problems due to air in my system. I am hoping this is it

 

Is this the bleeder valve on the passenger side firewall near the battery compartment??

 

Yes; it sounds like you're already venting it.

 

You need to run the vehicle and partially unscrew the bleeder valve repeatedly. if you are getting bubbles instead of straight coolant you still have an air pocket. On particularly difficult cars I will raise the front of the vehicle to help purge the air

 

Man I bled the car over and over, process took about 30 min. But every once in a while Id still get some bubbles appearing, eventually I would get just coolant coming out. I think I have the problem figured out, but this is one for the dealer. When the heater is on, cool air blows out. As others said, under throttle, the water pump forces coolant and pushes hot air into the cabin. I decided last nite to switch to AC. Heat continued to come into the cabin for almost 3 minutes after I had switched from Heat to AC. Once cool air started to flow inside from the AC, I switched back to heat. The same cool air continued coming into the cabin for up to 5 min after I had hit HEAT. The only time the cool air stopped, was once I hit the accelerator pedal. I think the valve which controls cool/warm air from coming inside is getting stuck or perhaps is clogged and only under throttle is forced open. Not sure....taking it to the dealer though....