My Oldsmobile is overheating

Last summer I let the oil get low and the engine overheated on my 83 Olds. I topped up the coolant and made it home no problem (300 miles). Now, however, if I take the car out for 15 minutes, the MOMENT I turn off the engine the coolant overflow reservoir starts boiling like Niagara Falls. Not until I turn off the engine...I can leave it idling in the driveway and the reservoir is perfectly calm. The INSTANT I turn off the engine it starts boiling like crazy, making a sound like a jet engine.

Would anyone care to offer me a diagnosis or a suggestion?

Marty from Winnipeg

Reply to
Jewish Cowboy
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I would like a little more information: Engine?

Do you have to add coolant or water regularly?

Any other particular problems with this car?

Depending on which engine you have, special situations may apply. We have a lot of activity on cooling problems on this newsgroup..

The solutions usually lie in the following: (1) Engine fan/fans not working properly. Can be electrical in some cases, or viscoelastic fan clutches in others. (2) Radiator plugged, internally or externally. Internally may be rust, rubber fragments, or mineral scale. Sometime requires taking it to a radiator shop for mechanical cleanout. May also be detritus in the radiator cooling fins, or trapped between the air conditioning (A/C) condensor and radiator. (3) In some cases can be collapsing radiator hose, to suction of water pump. (4) May be the water pump itself. (5) Could be an air bubble in the engine, where coolant should be (6) Can be a bad thermostat

And last but not least, and especially when an overheat situation has occured, it can be a blown head gasket, cracked head, cracked block. Some GM models love to do this. See "information" above.

Reply to
<HLS

"Jewish Cowboy" writes in article dated 26 Sep 2005

14:13:45 -0700:

Oil?

A coolant pressure increase after engine shutoff is normal. When the engine is running, the coolant is cycled from the engine where it absorbs heat to the radiator where it loses heat. When it stops, the same coolant sits next to the still-hot engine, causing higher vapor pressure.

Normally it's not an instantaneous effect, though. It takes at least a few seconds to get to boiling temperature. You might have too much water in the mix -- more anti-freeze will raise the boiling point so it doesn't happen so quickly (if at all).

It's also possible that your thermostat is inaccurate. It's a cheap part, so change it.

-- spud_demon -at- thundermaker.net The above may not (yet) represent the opinions of my employer.

Reply to
Spud Demon

Hmmm. 22 year old car. Where do we begin. With the coolant. What is the freeze point / boil point of the coolant as indicated with an antifreeze tester?

Next I would use a termometer ( infrared ) to read the temp of the fluid in the coolant overflow bottle during engine ON and immidiately afterwards during engine OFF.

Next, the pressure cap for your radiator/coolant reservoir might not be functioning correctly. On my *new* used car, the thing is set to open at 16 pounds / square inch pressure.

That means the system is pressurized, and therefore raises the boiling point of the fluid ( think of how a pressure cooker works ). If you have pressure cap gasket failure, this could be the problem, and it only requires you replace it with another one. Simple stuff so far. It can get worse from here out, but that is where I would begin.

Lg

Reply to
Lawrence Glickman

Start by replacing the radiator cap and making sure you have a 50/50 mix of antifreeze and water. Steve B.

Reply to
Steve B.

Was it really the OIL that got low, or was it coolant?

Sounds like a bad radiator cap to me, but since there was a previous overheating incident it could be a warped head, blown head gasket, cracked head, etc.

Reply to
Steve

Thanks to all those who replied. I believe I now have an explanation as to why the overflow reservoir starts boiling over at the moment the engine is turned off. My theory is that there is a pocket of coolant inside the engine that is overheated, but as long as the pump is on, it remains pressurized to the point where it cannot boil. The moment the pump turns off, the coolant pressure equalizes throughout the system...the overheated pocket instantly boils, forcing the system pressure to rise above the release point of the radiator cap. The coolant which floods into the reservoir, now at atmospheric pressure, begins to boil as well.

According to my theory, then...there is boiling water deep within the engine at a pressure HIGHER than the 9psi release point of my radiator cap...there is somewhat cooler boiling water in the overflow reservoir at atmospheric pressure...and there is water in the radiator, slightly above 212 degrees, which is sitting at 9 psi and NOT boiling.

One thing that ISN'T helping the situation is the sorry condition of my radiator. I took the cover off to clean out the fins, and after clearing out a bird's nest or two, I found that about 10% of the fins would disintegrate into a pink powder when I rubbed my thumb across them. So I'm not getting 100% cooling capacity.

Even so, I'm going to see if I can run with what I've got. First step is to dump the existing coolant (which has gotten pretty watered down after repeatedly refilling it with a hose) and fill the system with premixed antifreeze. This may bump up the boiling point enough to keep everything from gushing out when the pressure releases.

Thanks again to all those who contributed. I'm going to answer your points individually in separate letters.

Marty

Reply to
Jewish Cowboy

Hi "H"

I've posted a general reply to this thread, but I also wanted to answer your specific points. I'VE USED CAPS FOR MY ANSWERS (forgive the shouting)

(1) Engine fan/fans not working properly. Can be electrical in some cases, or viscoelastic fan clutches in others. FAN IS WORKING (2) Radiator plugged, internally or externally. Internally may be rust, rubber fragments, or mineral scale. THIS COULD BE. ALREADY CLEANED IT EXTERNALLY. Sometime requires taking it to a radiator shop for mechanical cleanout. May also be detritus in the radiator cooling fins, or trapped between the air conditioning (A/C) condensor and radiator. (3) In some cases can be collapsing radiator hose, to suction of water pump. I BELIEVE THE CIRCULATION IS GOOD. HAD THE RADIATOR CAP OFF WITH THE ENGINE RUNNING AND IT LOOKED LIKE NIAGARA FALLS INSIDE. (4) May be the water pump itself. CIRCULATION LOOKS GOOD. (5) Could be an air bubble in the engine, where coolant should be WOULD I CLEAR AN AIR BUBBLE IF I DRAIN AND REFILL??? (6) Can be a bad thermostat RUNNING WITH NO THERMOSTAT SO COOLANT SYSTEM IS GOING WIDE OPEN. And last but not least, and especially when an overheat situation has occured, it can be a blown head gasket, cracked head, cracked block. NO WATER IN THE OIL OR CONSPICUOUS LOSS OF OIL.

Reply to
Jewish Cowboy

Hi Spud

Thanks for your suggestions. I've posted a general reply but I also wanted to answer your specific points. FORGIVE THE CAPS.

A coolant pressure increase after engine shutoff is normal. When the engine is running, the coolant is cycled from the engine where it absorbs heat to the radiator where it loses heat. When it stops, the same coolant sits next to the still-hot engine, causing higher vapor pressure. NO, IT'S A PRESSURE decrease, NOT AN increase THAT CAUSES THE BOILING. THE COOLANT CHANNELS WITHING THE ENGINE ARE PRESSURIZED BY THE PUMP. WHEN IT SHUTS OFF, THE PRESSURE DROPS INSTANTLY. IF THE TRAPPED COOLANT IS HOT ENOUGH, IT WILL BOIL EXPLOSIVELY.

Normally it's not an instantaneous effect, though. It takes at least a few seconds to get to boiling temperature. You might have too much water in the mix -- more anti-freeze will raise the boiling point so it doesn't happen so quickly (if at all). YES, I WILL TRY TO CORRECT MY MIX. BUT IT IS AN INSTANT EFFECT. I SUSPECT A TRAPPED POCKET OF COOLANT IN THE ENGINE.

It's also possible that your thermostat is inaccurate. It's a cheap part, so change it. I'VE PULLED IT OUT ALTOGETHER AND THE PROBLEM PERSISTS.

Reply to
Jewish Cowboy

Hi Lawrence

Thanks for your input; I've posted a general reply but wanted to answer your specific points. FORGIVE THE CAPS...

Hmmm. 22 year old car. Where do we begin. With the coolant. What is the freeze point / boil point of the coolant as indicated with an antifreeze tester? WILL REPLACE IN ANY CASE WITH OPTIMUM MIX. Next I would use a termometer ( infrared ) to read the temp of the fluid in the coolant overflow bottle during engine ON and immidiately afterwards during engine OFF. BEFORE SHUTDOWN, ITS SITTING AT ATMOSPHERIC SO IT MUST BE BELOW 212. AFTER SHUTDOWN, IT GETS AN INFLUX OF HOT WATER FROM THE RELEASE OF THE RADIATOR CAP...THAT'S WHAT MAKES IT BOIL OVER. Next, the pressure cap for your radiator/coolant reservoir might not be functioning correctly. On my *new* used car, the thing is set to open at 16 pounds / square inch pressure. I THINK IT'S WORKING FINE. MINE IS SET FOR 9 PSI...ITS AN OLDER MODEL. That means the system is pressurized, and therefore raises the boiling point of the fluid ( think of how a pressure cooker works ). If you have pressure cap gasket failure, this could be the problem, and it only requires you replace it with another one. Simple stuff so far. It can get worse from here out, but that is where I would begin. I EXAMINED THE PRESSURE CAP CAREFULLY. IT'S AN INTERESTING SYSTEM. THE COOLANT CAN ONLY GET INTO THE OVERFLOW WHEN THE PRESSURE GOES ABOVE 9PSI. BUT I NEVER UNDERSTOOD HOW WATER GETS BACK INTO THE RADIATOR UNTIL I NOTICED THAT THERES A KIND OF CHECK VALVE BUILT INTO THE MIDDLE OF THE DIAPHRAGM. WHEN THE ENGINE COOLS DOWN AND DEVELOPS A POSITIVE SUCTION, THAT'S WHEN YOU DRAW WATER BACK FROM THE RESERVOIR. IT DEFINITELY DOESN'T WORK BY GRAVITY.

Reply to
Jewish Cowboy

Water pumps don't generate measurable pressure, they just move water. The pressure in the system is generated by expanding water in a sealed system. When you turn off the engine the pressure goes up because the engine continues to radiate heat in to the water but the water is no longer moving and being cooled by the radiator.

Steve B.

Reply to
Steve B.

I disagree that the pressure generated by a water pump is negligible. It's hard to engineer an effective heat transfer system without some pretty healthy flow rates through a lot of long channels, and that all adds up to a significant pressure drop. At least five or ten pounds, which probably represents at least thirty degrees of boiling point elevation.

That's why I conclude there is a trapped pocket of overheated water somewhere in the engine block. At the moment the pump shuts down, the pressure in the radiator can only go up, as it's exposed to the higher pressure of the engine. That means the radiator won't start to boil right away...furthermore, the fins are cooler than the water inside, so the radiator can only move farther away from the point of boiling. Within the engine, there is an immediate pressure drop...but only to the level where the engine pressure equals the radiator pressure, which I already concluded was NOT boiling. So unless there is some water in the engine which is significantly hotter than the rad water, the engine also won't boil.

Yes, I agree with your point that the engine can now begin to radiate heat into the water, possibly bringing it to the boiling point. But you didn't have the benefit of observing how sudden and violent was the onset of boiling...demonstrating that it was not a gradual process as you described, by the onset of a sudden instability which I associate with the shutting down of the pump.

I believe I have now stopped the problem by changine the radiator cap. I went to Canadian Tire and asked for a 9-pound cap for my 83 Oldsmobile. They checked several models and every one showed a 16-pound cap. So I took the higher pressure unit and installed it, with good results. I don't know why I was driving around with a 9-pound cap, or why I got away with it until my recent overheating episode. I plan to monitor the situation for a couple of weeks before draining the whole system (I'm now running on about 80% water) to try to get rid of entrapped air, and then refilling with 60-40 for the onset of the cold Canadian winter.

any trapped air

Reply to
Jewish Cowboy

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tim bur

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