The engine temperature has been perfect. heats up within a normal amount of time.
Coolant is topped off and I don't think I have any orange build up on the bell-housing.

at idle I have no heat, when the RPM's are up I only have a little heat if the fan setting is at 3 or below. 4-10 blows cold air.

I replaced the thermostat and ECT sensor with no change.

At idle I took both hoses off the heater core an noticed there was barely any coolant flowing through it. maybe a small amount at higher rpm.

What controls the flow to the heater core? I thought it might have a clogged heater core but the no flow into the core kinda ruled that out.

If its the water pump, how is the engine temp staying perfectly in the middle of the gauge?

Please help. Its freezing up here!

 

How did you see no flow to the core? I think is the core itself.

Also another way to troubleshoot is try to turn on the AC, if it doesn't turn on is probably your control module, the one with the buttons and stuff.

 

While the engine was running I pulled off the two hoses going to the heater core. at idle there was nothing coming out of either hose. As the rpm's went up a little came out the inlet hose but definitely not a lot.

The a/c works fine, it seems like there is only a small amount of flow through the core.

Id like to bypass the core with a piece of clear tubing to see if the flow picks up a lot with the system fully pressurized.

 

A long shot could be your water pump but I doubt it since the car is not overheating, but agian, the outside tempereature could be keeping it low.

 

there is a flap that could be failing to let coolant flow from your waterpump to your engine. Either that or it is yes your waterpump.

 

Would that flap be causing the heat to stop flowing to the core? if so where is this flap?

 

I had this problem.......flush the core using 2 lengths of hose and a couple of soda bottles. Fill the core with boiling water using 2 laenths of hose, add some CLR and let soak for 1/2 hour, then rinse/flush with clean water. Hook up a 2 liter bottle to each flange and sqeeze one bottle then the other thus flushing the core. Now you must bleed the core.....this is the important part, remove screw fastening the expansion tank and raise/block it up as high as you can get it. Fill the tank full, start the engine and hold rpm's at 2500 then pull the upper core hose half way off exposing the bleed hole in the hose to allow air out of system. Be very patient air will come out of this hole in the hose (it's under the clamp). Make sure the tank stays full, take your time. Ask me how I know this, my dealer didn't.

 

I think somewhere near the water pump. dont quote me on it though cuz my car had this problem and i had to replace my waterpump as stock ones tend to go bad.

 

I have just flushed the core with CLR and high pressure hot water. A ton of sediment came out I burped the system, and had to add almost a half gallon of fluid!
OK so now I have heat at 2000 rpm and up, but I still have no heat at idle.
I put a piece of clear tubing after the core in between the core and the engine to monitor the flow though the core. As expected, none at all at idle, and some at higher RPM.
Any clues now?

 

Which year/engine?