Overheating: We're all stumped

overheating

#1

Not too long ago I had posted regarding accidentally shiting to park while still moving slightly. (Good news is the transmission is just fine; it’s due for the 30K transmission service anyway and they’ll flush it out then to double check.)



Well the big issue I’ve been having with my beloved 1994 Pontiac Grand Am is consistant overheating problems. I’ve been extremely careful never to let it reach the point of boiling over; I stop once my car is around the 250 degrees mark so that it doesn’t hit the red. But my mechanics are absolutely stumped. Four years ago I had the heater core replaced. Two years ago it was the radiator. This past January it was the coolant resuvoir, the themostat, and a massive plastic pipe in the middle of the engine. In May it was the water pump. Most recently it was the temperature sensor, the relay, and the fan motor.



All these things replaced, and it’s still getting too hot! The shop did a coolant flush in case the core was gummed up last weekend, and they bled the air out after to prevent air bubbles. (This was all free of charge thankfully since the last repair for the same system was within thirty days.)



They notice that if you put it in neutral and gun the engine, sometimes that is enough to cool it back down. If it’s getting near red and I shut the car off completely and turn it on, my fan actually comes on properly (but otherwise it won’t.)



The strangest thing: it only does this on COOL days. When it rains, or now that the morning temperature is back within the 70s, it heats up too fast. When it’s hot outside it doesn’t seem to have a problem at all . . .



Could rain or morning dew be shorting out something? What part has yet to be replaced in this cooling system? This appears to be a very frequent problem with the early 90s Grand Ams, so I suspect there’s an obvious solution we’re all overlooking . . .


#2

There are only a few things I can think of that haven’t been addressed. It’s uncommmon, but I’ve seen a radiator hose collapsed on the inner ply, restricting flow in the hose, but not on the outer ply so the hose looked good from the outside.

I’m also wondering if this car has an air dam under its chin to direct air through the radiator and that’s missing.

If this is truely a problem common to these cars, perhaps there’s a TSB (technical service bulletin) that the dealer could help you find.

Lastly, perhaps there’s an air bubble in a high spot that’s blocking flow and needs purging.


#3

If the cooling fan isn’t coming on, sometimes, change the engine cooling fan relay. If this doesn’t do it, hopefully, someone will break out the voltmeter and wiring diagram, and do a little electrical checking.


#4

We had that replaced not even three weeks ago . . . We’ve replaced, in this car’s lifetime:

Heater Core: (2 years ago)
Radiator: (2 years ago)
A giant plastic hot water pipe from deep in the engine (don’t know what it’s called but it was pretty disintegrated): January 07
Many of the radiator hoses: January 07
Water Pump: (May 07)
Thermostat: (January 07, replaced again in May on warranty)
Temperature sensor: (August 07)
Temperature relay: (August)
Fan motor: (August)

I just dropped it off at the garage again. My mechanic is determined to get to the bottom of this; he’s viewing it as a challenge.

While I was in there I told him to go ahead and do the 120K mile maintenance stuff even though it’s still 119300 miles. -_- Might as well get it all done now if they’re gonna keep it for another weekend. (Since most of this is considered warranty labor I’m low priority XD Cheap, yes; fast, not on your life.)


#5

Verified: There is an air dam, and it’s still attached.


#6

What is the ACTUAL temperature of the coolant when the gauge says “250?” This can only be ascertained with a calibrated thermometer or infrared heat gun. Perhaps the engine is not as hot as you think it is. Has anyone tested the gauge itself?

I know this is a long shot, but I can’t find the words “radiator cap” anywhere in the list of things replaced. A bad cap can cause overheating.


#7

I know this is a long shot, but I can’t find the words “radiator cap” anywhere in the list of things replaced. A bad cap can cause overheating

I was just thinking the same thing.


#8

I left that out. But it was replaced.

Mystery is solved: The head gasket is going, although it’s not completely blown yet.


#9

As the years have gone by, and it’s had the overheat problem, I’m sure the mechanics have, often, done coolant sysem pressure checks with the engine cold, and with the engine hot?


#10

They have, but this morning they let it sit and idle for much longer than before, and that’s when they noticed a very small amount of steam coming from the gasket area.

My mechanic was shocked to learn that it has lasted almost 120K miles, since the quad 4 engine had notorious head gasket problems. He thought it had been replaced before.