Weird overheating problem

[Carlspike]

The car is a 1992 Z24 DOHC. The car has started to want to overheat recently. In the spring I replaced the radiator and the water pump. The pump was a "updated" version with different fins for supposed improved flow. The car has ran at higher temps ever since then. Before the pump it never got past half way on the gauge, but then it started to run between half and 3/4. Oddly enough once it got colder in the fall the temps started to rise, past 3/4 and even almost to overheating. When the temp rises if I shut the car off and re-start it (even without it sitting) then the temp won't go as high. It also won't run hot in town, but on the highway it wants to run hot. After driving it for a while the temp will calm down and end up between half and 3/4. It seems to be the opposite of how a cooling system should operate (running hot on the highway and in cooler weather.) I've bled the system many times and never get any air out of either bleeder screw, only coolant. Any insights into this cooling system?

[Carlspike]

bump... anybody?


how difficult is the T-stat?

[IsaacHayes]

I think I remember reading somewhere that someone switched to the new style pump or a different one and it did cool worse. I would replace the thermostat first before chasing other things. It's a 92 so I take it doesn't have dexcool but it may have long life/extended life coolant which is the same stuff that they sell everywhere now. It is possible that it's clogged up the radiator or heater core but I would do the thermostat first as that is suspect if it's old.

[Carlspike]

I repaced the t-stat and there was no change. So I put a remanufactured pump in (old design) and now it works great. I don't know if I got a bad pump or of GM's new design sucks.

[IsaacHayes]

Cool, that confirms it then! Old is best! hehe.