heat blows warm at idle

[RoB51988]

I just back flushed my heater core because it was clogged solid. It seems like when Im at idle or at a red light it will blow warm but when Im driving it blows hotter. Not sure if this is a sign of bad water pump or coolant leak some where? any ideas?

[KanTech]

It sounds like a problem with the flow. If your heater core was so bad that it was indeed 'plugged solid' as you say, then it would be safe to assume that it is probably still restricted even after your attempt at cleaning it. The flow from your water pump is based on the speed of your engine...the higher your engine RPM, the faster the pump turns thus creating more pressure or flow. A restriction in the heater core would account for the change in vent temp that you are concerned with.
I would recommend confirming this with your technician, and/or replacing your heater core.
Cheers,

[Dave_s]

Could also be worn down impellers on the water pump. Once they go flat, the pump will need to move faster in order to get enough flow through the heater core. I would start by replacing (or at least pulling and checking) the water pump. Its less time consuming and cheaper. If that doesn't work (or the blades aren't gone), its time to replace the heater core.

I am assuming that when you flushed the heater core, you removed enough of the junk to get it flowing well again. You may want to try and flush it again first.

[Doug Tatham]

Another thing to check is your temp gauge. If it climbs up when your idling then it means there isn't enough circulation and it could be the water pump. Sometimes the impellers come loose and don't spin except at higher RPM's.

[tripletdaddy]

If you cut loose a lot of junk, it may plug up the thermostat and cause it to overheat.

[raybuick]

I'm expreiencing the same conditions also. After i flushed it, the heater worked great but since i replaced the coolant overflow tank because it had a hairline crack with a new one, the heater has cooled down alot. It was almost blistering hot before. I'm thinking the water pump blades are deterioated or thermostat is stuck open. Also I think the engine is overheating a little, because I hear the rad fans kicking on too often. This of course keeps the temperature in check. I'm thinking about disabling the fans to see if the temperature holds.

[shorod]

If the thermostat is stuck open, the engine shouldn't overheat. Since the fans are kicking in, I don't think you have a problem with an open thermostat. You might however have air in the cooling system since you've recently had the system open.

-Rod

[RoB51988]

Well what would be the best way to get the air out of the system? Ive opened the overflow tank and let the car run with the heat on high

[shorod]

That should be a good start. Any chance you can get the car positioned so the recovery tank is the highest point of the cooling system?

-Rod