I have a 93 civic ex coupe. When driving at highway speed 75+mph for a long period of time, the temp guage begins to creep up almost to the top. When the heat is blasted, the temp drops a bit. I have replaced the waterpump and thermostat. Fan is functioning properly. The coolent is full and clean. No signs of leaks or white smoke. At lower speeds temperature falls back to normal..Clogged Radiator? Clogged Heater Core? Someone please help!!

 

First test these ideas by thoroughly flushing the cooling system. If that doesn't work, compression test the cylinders and a do leak down tests.

 

Probably the radiator needs replaced. Besides internal clogging, they can also fail because the fins corrode and fall off the outside. This drastically reduces the efficiency of heat transfer.

 

i have also found that if the oil pump is going bad, the right pressure will create additional heat. found that the hard way

 

I am also having the exact same issue. 92 ex sedan (not trying to hijack the thread) I just replaced my thermostat and did a flush, fans also working fine.

On a leak down test.. can i take my compression tester and just leave it sit for a few minutes and see if the pressure drops?

 

*bump*