1998 grand prix overheating problem

pontiac

#1

My girlfriends car has been overheating for two weeks and no one seems to be able find the cause. Here is her brief on the process so far. P.S. Now both her and the car are overheating.



Engine Cooling problem

1998 Pontiac Grand Prix V8 Front Wheel Drive Automatic 60,000 miles

I noticed the car temp guage had stopped running at the usual 190. Took the car to the mechanic. They replaced the water pump thermocouple, changed the oil, did a compression test, changed the fan relay switch because the fans were not coming on once the car got to 240 and higher on the guage. They hooked up the computer and found the guage to be reading 10degrees higher than what it actually is. I’ve replaced the radiator cap. I had them replace the thermostat 3 times now, to no avail. I have checked to see if the coolant reservoir was sucking in or blowing bubbles, starting the car cold with the cap off. I took it to another garage that insists the head gasket is blown. There is no water, white specks on the dip stick and there is no sludge in the reservoir and nothing coming from the exhaust. They said there was a grounding problem with one of the fans. The other is not working because the air conditioning is down, clutch as well. There is nothing coming from the tail pipe. The hose to the radiator gets hard. If you release the pressure, the fans both kick on and start running. The inside of the car seems as though hot air is on when it is not. HELP


#2

I won’t say that I can make heads or tails of that description, but someone with an IR thermometer could pretty easily check the radiator for indications of blockage.

Why do the people at “another garage” insist that the head gasket is blown? What were the results of the compression test?


#3

Yeah I bet the shop that is insisting that a head gasket is blown is correct. This car has been overheated so many times and so many things have been replaced that the chances are very high. A blown head gasket does not necessarily mess up the oil, or spew steam from the tailpipe, or make bubbles in the overflow.


#4

So right now you know the water pump is working, the thermostat is good, the temp gage is working, the fan relay is good, and the fans are working (?). You haven’t really told us whether the “grounding problem” was fixed or whether its fan was tested. That info would help.

Because the engine has been repeatedly overheated, I’d start with a compression leakdown test, also called a pressure leakdown test. It’s a simple test where a pressure gage is attached to each spark plug hole, air pressure is pumped in, and the cylinder is monitored to see of it holds pressure. That’ll determine whether or not there’s a headgasket breech. Honestly, if the headgasket is brecehd I’d think about a replacement vehicle. If the headgasket breech is in the rear cylinder bank it’ll cost a bundle to replace.

If that tests good, I’d take an infrared pyrometer (cigroller’s idea) and look for erratic temperature spots in the radiator, searching for possible evidence that the radiator wasn’t flowing properly through all its tubes.

Another possibility is the radiator hoses. The inner liners can collapse and restrict the flow of coolant. I’d just replace them. They’re cheap.

One more possibility is a water pump with an eroded impellar. A pump in this condition will push some coolant, just not enough. A flow test can be done on the water pump.