Weird Cooling Problem

[KenC]

I've been having some trouble with my cooling system and I'm not sure what to attribute it to.

I replaced the block recently and subsequently replaced all of the coolant.

My thermostat has about 5k miles on it, and the water pump has about 300 miles on it.

I have properly bled the system three times (waiting for the thermostat to open and the bleeding on an incline).

My problem:
During extended amounts of driving (over 20 minutes), the temperature gauge begins to creep up to the mid mark and exceeds it by a minute amount. This is above the normal opperating temperature.
I also find it strange that my heater temperature (blower heat) varies greatly upon the rpms of the engine. I understand that due to the increased velocity of the coolant flow when the water pump is moving faster that the temperature may increase slightly, however, if I drive above 3,000rpms for more than 30 seconds, the heat becomes unbearable (it becomes painful to hold my hand in front of the vent). If I drive at low rpms or idle, the heater temperature decreases.

Does any one have any idea what could be causing this?

[txleadfoot]

I'm having similar problems as well on a fresh rebuild (new water pump, 2k miles on thermostat). I haven't heard of the incline trick though, can you elaborate?

My temp runs between 1/2 & 3/4 mark on the gauge which is worrysome. The heater ONLY blows warm while idling. Once I begin driving, the heater blows cold.

When I flushed the radiator, plastic water pump bits came out. I'm wondering if more bits are lodged in the heater core.

UPDATE:

I swapped the heater core hoses at the firewall. Now I have heat again! The temp gauge now reads a hare past 1/2. Thanks FredK!

--Shaun

[KenC]

When the front is inclined, the air bubbles are more apt to move toward the bleeder valve.

[Gray S.]

My m42 runs just above the half usually also. Sometimes in traffic it gets to have about a needthe widths space between the needle and 3/4 mark. It used to run higher on the gauge, but then I quickly cleaned out the grounds on the back of the cluster and that dropped it a little bit.

I still dont know what makes it run just over the 1/2 though, I really want to figure it out as it just bothers me. If you guys figure something out please post it, I'm sure we arent the only ones with this issue.