Overcooling or Water Pump?

[troverman]

We changed headgaskets back in the spring. We have never used the heat since then until now. We did replace the t-stat. The car has run fine and never overheated since. (about 7k miles). Now that its cold, the car takes a long time to get fully warmed, and has zero heat at idle; it just blows cold air, even if the car is fully warmed. However, if the engine is revving (either while driving or by holding the gas down to about 1500 RPMS) then there is heat which is hot. After having great heat on a long drive, if the car sits and idles at a stop light for a while, the heat turns lukewarm and then cold.

What is causing this? I have watched realtime engine data on my scanner, when it is 30F outside the engine warms to about 180-190F; it just takes awhile.

[Disco Mike]

Might want to consider bleedin the air out of the engine. Many time when head gaskets are replaced, all the air is not removed when adding coolant.Try something, start the engie from cold, turn the heater to high and high fan speed. If when the engine the heater doen't heat at an idle then run the rpm's up to 2000 and if within a coulple of seconds you start to feel heat, you have air trapped.
Mike

[troverman]

What is the proper procedure for bleeding air from the system? I know it involves removing the small cap on the upper rad hose.

Thanks

[auwesman]

Unscrew that small cap, and unclip the overfill tank and lift it up.
Run engine and pour fluid in until water starts seeping out of bleed screw. Retighten bleed screw (careful not to break it, it's cheap plastic), fill overflow tank and check heater for heat. If you get hot heat, then you should be good.

[Disco Mike]

Better yet, when cold, remove the bleed screw, and fill the coolant bottle till coolant starts coming out the bleed screw, then replace the screw and coolant cap.
If it continues, redue the steps one more time a day later.
Mike

[KDamericano]

It helps if you've on an incline too...