Engine sporadically overheating

[lithdoc]

Hello folks,

I have a new problem with our 89 MGM. About a month ago it overheated. We towed the car home.

We thought this would be the thermostat as the upper radiator hose would appear very tense under pressure and it even burst open around the heater valve. We took the thermostat out, but the problem seems to continue, although sporadically. We drove close to 1000 miles with just water in the system mostly glitch free and now it started happening again. We then changed the water pump and that still has not resolved the problem. The car the proper antifreeze in it. No thermostat in the system. No leaks. New water pump. It seems as if it starts to boil over somewhere within the system causing buildup of pressure and it just overheats.

Please advise. Thank you!

[BigT]

Just from my experience, make sure to burb the system so there is no air pockets preventing water flow. Speaking of water flow, can you see it flowing into the radiator with the cap off? Maybe there’s a blockage or collapsed (pinched) hose somewhere.

[lithdoc]

How do I get rid of the air pockets? After removing the radiator cap I see boiling water.

[BigT]

Be careful with hot parts and cold water. I would let everything cool down first. After that, fill up the radiator with water to the top. Squeeze and let go the upper radiator hose. You’ll see it burb and the level go down. Refill and burb until it stops. Start up the car. Since you don’t have a thermostat, you should see the water start flowing right-a-way. If it’s not flowing, then you have a blockage somewhere.

[VicCrownVic]

Is it possible that a failing fan clutch could be to blame?
You (or your brother) can spin the fan by hand (with the engine off of course) and (someone correct me if I'm wrong) I think if it spins freely the clutch is bad/going bad.

[BigT]

You might have to add water when it first startups up if there are other air pockets the water pump will fills up as it runs.

[DerekTheGreat]

What water pump did you throw on there? I read something awhile ago about what happens when you put a reverse flow water pump on, that it can be bad. Also, like Vic mentioned, check the fan clutch.

[jaywish]

like above, if the car is cold, disconnect the upper hose from rad. Turn on car, with a proper working pump, water should gush out with no thermostat in place.

To check fan clutch, find someone to help. Engine should be at full operating temp. Have helper start the car. You look at the spinning fan. When you are ready signal helper to turn off car. The fan should stop spinning very quickly. (1 revolution, maybe 2)

If those work I would replace the radiator.

Maybe others have something else to check before R&R the radiator.

[WagonMan]

You can't expect the engine to cool without a thermostat. With no thermostat the water doesn't get forced thru the block, it just circulates around the radiator. I had a similar problem with over heating and it was the bottom radiator hose sucking itself closed. There should be a wire coil spring in the bottom hose. My two cents. WagonMan

[jaywish]

Yup, Not that a suggestion from wagonman needs my agreement, but he is right.

check for gush/flow then add back thermostat, then check the rest of the stuff.

[gadget73]

If the radiator is original, or if it looks at all crusty at the ends of the tubes, replace it while you're putting the thermostat back in.

[lithdoc]

Slight complicating factor is that the car is in Europe... Placed a flush solution but who that did not seem to help.

Will report on the fan clutch. Burping the system did not help. It seems that the block is overheating and it simply starts to boil over the radiator cap out through the reservoir.

[Rodentkiller]

The head Gasket may be bad in this case use some head gasket leak decter or use a "smog" matchene to sniff HC's in the radiator if Hc's are found in the radiator need head gasket replacement.

[GM_Guy]

Is it possible that a failing fan clutch could be to blame?

Absolutely. Even when doing highway driving. Theres a misconception that the fan does nothing when driving at highway speeds, it does.

Quicky test; get car good and hot (drive it). Open hood, watch fan, turn off engine, fan should not keep spinning when the engine shuts down. It may turn a fraction of a turn, but if it keeps moving its bad.

Alex.

[lithdoc]

So, a quick update. Head gaskets have been replaced, and the long-time evasive vacuum leak has been found. The motor runs very very smooth now, like never before! Overheating problems appear to have been fixed, although only time will tell.

One new issue, however. We had permanently affixed the fan to the crankshaft, ruining the clutch in the process. Now the car whines rather loud as the fan speed is directly linked to the RPMs. I need a new clutch and I see there are two types - thermal and non thermal? Which one should I be getting? How to determine which one I have? Thanks!