Engine overheating when Idle

My engine has recently begun to overheat whenever the car idles or moves at slow speeds. When I speed up and travel at higher speeds, the temperature starts coming down. It starts going back up again really fast at a stop light, etc..

I suspect this is a problem with the thermostat. During idle, there is not enough pressure from the radiator for the thermostat to regulate the coolant flow to adjust the temperature. Is this right? Do I need to check my water pump and radiator too? Will replacing the thermostat fix the problem?

Let me know.

I'd check the water pump carefully - if it's leaking at all replace it.
Also check the thermostatic fan clutch if you have one. If you do replace the water pump you might as well replace the thermostat at the same time, but if it cools off when underway I doubt that's your problem. It might even simply be gunk buildup in your radiator that will require either rodding out or replacement.

good luck

nate

You are describing a dead clutch on the rad fan.

To check, heat up the car and watch the fan while someone shuts off the engine.

A working clutch will stop the fan almost instantly. If the fan keeps spinning, the clutch is dead.
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's

"Mike Romain" wrote

Yeah....the f-bodies haven't had mechanical fans for years now.

My car is a Pontiac Firebird, 1995 with 106500 miles. It overheats at all ambient temperatures (50F - 90F). Actually it happens with AC both off and on but the temperature rise is more pronounced with the AC on.

I had my radiator flushed about 3 months ago for this same problem but that did not fix it. I replaced the coolant (with the 50/50 mix) about 2 months ago. Its been over 2 years since I last checked the water pump, drive belt, etc..

Is your fan working?

No this is not right.

As long as the thermostat can see coolant, it will open at the correct temperature regardless of pressure in the cooling system.

Overheating only at idle would tend to suggest an airflow problem.

Check the cooling fan.

first thing i would check and see if electric fan comes on.the quick way to do this start come up to engine temp let settle down to idle then unplug engine coolant temp sensor the fan should come on if it does this means the fan relay and fan are doing what suppose to.i have had cutless supreme.olds calais. cutless curser station wagon delta 88 chevy luminia all did this same thing with over heating found in water pump empeller rusted away on a couple paddles were left and part of them were missing.look for leaks in heater lines gm seems to be prone to do this.also intake manifold air intake and has a water port on one end it is plastic and prone to cracking letting water to leak in engine intake.this is what i found on my gm products.i am going To buy another gm when time comes.



ps: also beware theirs a drain for a\c evaporator on fire wall your heater core may have a leak you will see antifreeze comming out drain this will cause overheating

Post edited by: hobbist, at: 2008/04/03 19:37