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HELP Overheating at WOT


JBellELDO

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My 1994 ETC overheats when I open it up on the highway. Then it looses all the coolant through the surge tank overflow tube. I read almost all the overheating posts and all I came up with for my symptoms was a head gasket-overheating under heavy loads, ie. hills or WOT. Fans opperate at 223 and the thermostat was just replaced. Doesnt leak coolant anywhere.

-Jon

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My 1994 ETC overheats when I open it up on the highway. Then it looses all the coolant through the surge tank overflow tube. I read almost all the overheating posts and all I came up with for my symptoms was a head gasket-overheating under heavy loads, ie. hills or WOT. Fans opperate at 223 and the thermostat was just replaced. Doesnt leak coolant anywhere.

-Jon

You can't conclude that the headgaskets have failed without proper diagnosis. Check to make sure the surge tank is filled to the proper level - 1-1/2" below the neck. Check to make sure the coolant concentration is 50/50 (freeze point of -34F). With the engine idling, remove the 3/8" line that leads to the surge tank and verify that a stream of coolant is peeing out of the hose.

Check the waterpump belt tensioner for free movement - lube the pivot point if it is sticking.

If the above items check out, remove the spark plugs put each cylinder at top dead center on the compression stroke and pressurize each cylinder with 120 psi shop air using an adapter. If there are bubbles in the surge tank, the headgasket is leaking. Continue checking the remaining 7 cylinders in this manner. If you do not see bubbling in the surge tank, the headgasket(s) are OK.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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Check the waterpump belt tensioner for free movement - lube the pivot point if it is sticking.

Yes, this is what I would suspect for overheating under load.

Jason(2001 STS, White Diamond)

"When you turn your car on...does it return the favor?"

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now would it make any difference if i told you that it overheats when i floor it and it down shifts when at high speeds, but when i am cruisin at, say, 35 and i give it a a little gas, not enought to make her downshift, she will cool down a few degrees instead of heat up or overheat? The overheating is more of a highway or highspeed issue. In town it stays around 210-220+- a few degrees either way.

-jon

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now would it make any difference if i told you that it overheats when i floor it and it down shifts when at high speeds, but when i am cruisin at, say, 35 and i give it a a little gas, not enought to make her downshift, she will cool down a few degrees instead of heat up or overheat? The overheating is more of a highway or highspeed issue. In town it stays around 210-220+- a few degrees either way.

Yes -- this is why we're suspecting a glazed water pump belt, or a tensioner that's lost tension, or perhaps both. The water pump is a "drag" on the system...it requires force to turn. If the tensioner has lost tension, the water pump belt can easily slip on the water pump pulley, which slows the pump down during those high-load situations and doesn't circulate enough coolant to keep the engine cool.

It very well could also be a head gasket, especially if the coolant level drops without overflowing. We're just suggesting to also check the easy stuff first, and not to reach the "head gasket" conclusion until you have strong evidence (like that pressure check).

Jason(2001 STS, White Diamond)

"When you turn your car on...does it return the favor?"

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Hi All,

Haven't posted in a while, but read site every day. JBelleldo you mentioned that the thermo was changed. Did you put a A/C delco in? My post are on here about overheating and i changed everything except the head gasket. My car was running fine but because what i went through last winter i did not want to take any chances. I took it to a mechanic that use to work for Van Buren chevy dealership in floral park. He did every test possible on my car. Everything checked out fine but it still ran between 215--and--220. He took out the thermostat and put in one from the dearler and now i run at 200-210. It seems that these cars need, and require GM parts only. Aftermarket parts don't seem to work well in Caddy's

PS I hope everyone on this site is doing well

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Continue checking the remaining 7 cylinders in this manner. If you do not see bubbling in the surge tank, the headgasket(s) are OK.

Great suggestions from the guys.

A few years ago I had the exact same symptoms as you're having. Mainly long hills at highway speeds would produce the most overheating. Short "clean out" runs thru the gears didn't seem to cause much change in temperature.

I had to add coolant every few weeks. No visible leaks.

After a thermostat change, and all the other inspections, nothing was found.

I finally did the cylinder pressure test and # 5 bubbled in the coolant.

I actually never saw any bubbles in the expansion tank, however you could definitely hear them.

I had three pulled head bolts. The head gasket looked fine. Just the clamping force was gone with the loose head bolts, which allowed cylinder gasses in the cooling system.

Timeserts and a head gasket "fixed her right up".

I hope yours is a simple fix.

Barry

2008 STS V8
2016 Colorado Z71
1970 Corvette LT-1 Coupe

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ok didnt get to it last night, gonna give it a try today...being at a military school doesnt allow me much free time... anyway, i dont think mine is leaking coolant anywhere, just when the surge tank overflows. If it were a head gasket would I not see coolant in the oil or vise versa? just curious. I didnt pay much for this car and i dont want to have to pay what i paid for it just to get it running well. but i will take a look at the lines and the waterpump belt and tensioner today. also, if i choose to do a compression test, could i get the equipment to do it myself, or is that yet another thing to throw a few hundered down on? oh, and i'm not sure if the thermo was ACDELCO, ill get one from the dealer as well. im gonna be busy this weekend, but what better way to be busy than with your caddy? ph34r.gif

-Jon

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ok didnt get to it last night, gonna give it a try today...being at a military school doesnt allow me much free time... anyway, i dont think mine is leaking coolant anywhere, just when the surge tank overflows.  If it were a head gasket would I not see coolant in the oil or vise versa? just curious.  I didnt pay much for this car and i dont want to have to pay what i paid for it just to get it running well.  but i will take a look at the lines and the waterpump belt and tensioner today.  also, if i choose to do a compression test, could i get the equipment to do it myself, or is that yet another thing to throw a few hundered down on?  oh, and i'm not sure if the thermo was ACDELCO, ill get one from the dealer as well.  im gonna be busy this weekend, but what better way to be busy than with your caddy? ph34r.gif

-Jon

One more thing, make sure your coolant concentration is 50/50 using distilled water using a coolant concentration testor, Mike

Some have used old spark plugs, and they break out the porcelon, and drill and tap the top of the spark plug to accept an NPT 1/4" quick release fitting so that you can use a compressor to pressurize the cylinder (AFTER its at TDC and both valves are closed). If you do a search here you may find more information. But I would pressurize to 120 PSI, take the radiator cap off and listen and look for bubbles.

This is a classic thread discussing the home made adaptor:

http://caddyinfo.ipbhost.com/index.php?sho...58&hl=porcelain

see this link for the coolant tester

http://caddyinfo.ipbhost.com/index.php?showtopic=7738&hl=

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Since heat production is a function of horsepower being used, it appears your production is exceeding your rejection. One place to look is the front of the radiator. It is behind the AC condenser and cannot be seen or truely cleaned unless you REMOVE the radiator. Any car that has been on the road 5 or more years will accumulate large amounts of dirt and debris which will affect total heat rejection.

Regards.

Jim in Phoenix

Jim in Phoenix

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Since heat production is a function of horsepower being used, it appears your production is exceeding your rejection. One place to look is the front of the radiator. It is behind the AC condenser and cannot be seen or truely cleaned unless you REMOVE the radiator. Any car that has been on the road 5 or more years will accumulate large amounts of dirt and debris which will affect total heat rejection.

Regards.

Jim in Phoenix

I have had good results blowing it out with compressed air and then flushing with a garden hose. I was amazed at the crap that came out.

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Ok, i did some work, ran into some small problems, but i did all im gonna before i get rid of the car. I took the cooling system apart and replaced the waterpump the belt. It was pretty glazed and cracked, so that may have been the problem. Anyway, after i got everything put back togeher, im still a little low on coolant, would that be why the temp would be hangin out around 220? right after i stared it up, it went down to 196 and then after about 5 mins was up around 220-223 ish. Anyway, tomorrow im gonna fill her back up and see how she runs then! Wish me luck, if this doesnt work, prepare to see an Eldorado for sale soon!

-Jon

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Patience.

It sounds like you may have found your problem, and we would be thrilled if you did. It takes a full warm up, cool down cycle for the proper amount of coolent to be pulled in, keep the coolent up to the hot mark when the car is at operating temp. I can not stress how important the 50/50 mix is.. Sounds like you may be ok, let us know how this turns out, Mike

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ok, heres what happened today. Tried to head back to school in missouri today and it ran between 199-203 for probably 20 minutes on the interstate, then out of nowhere, it shot up 2 degrees by 2 degrees all the way to 250 and thats when i shut if off and pulled off the interstate. I let it cool to 230 and stared it, but it would not cool its self off, it would just slowly being to heat up again. Then after letting it cool to below 220, i started it and drove slowly to the gas station, on the way there i slowly cooled itself down to 207.

When I first got on the interstate, I began to accelerate on the on ramp. It first cooled itself from 208 to 207, but then began to quickly heat up until i was about a half mile past the on ramp going 65 it hit 250 where i shut it off. From there on is where the above too place... What is going on!?

I want to do a compression test to check the headgaskets but i dont have time to make the DIY adapter out of the spark plug. Can I take it somewhere to have it done, or does anyone around the KC area have experience with this? I need all the help I can get now. I'm out of money and I don't have a working car...

-Jon

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I didn't see this mentioned, if it was I am sorry. You have a 1994 also, as does rollingthunder. Our Guru solved Rollingthunder's overheating problem early in 2005.

Check page 4 of this thread, but review the entire thread to see the symptoms:

http://caddyinfo.ipbhost.com/index.php?sho...&hl=bleed&st=45

Here was his answer on Page 4, you have the same bleed line:

Hi All,

You guys are F_cking incrediable. Bbob, your the best. OverHeat problems fixed.

Last night after work, i decided to change all the small coolant hoses. I took off the metal line that runs from the surge tank to the water pump, no blockage. I then decided to take out the hollow bolt that is in the water pump housing. There was my problem. There was a piece of hose stuck in the hole, which was blocking correct coolant and air flow. After putting new hoses on and cleaning the nipple, i drove the car around this morning for about 3-hours. In traffic the hottest it got was 205-degrees. Once i started driving it went down to 201-and stayed there. I'm going to let the car cool for a couple of hours, recheck the tank, and top off if necessary.

Thank's again guy's without your advice i would have been spending money, without solving the problem

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I've got to agree. A gradual temp climb indicates a reduction in cooling ability via the system - not from a coolant boil-off or head gasket pressurization which are more sudden.

Check the system for blockage and confirm that the t-stat is OK.

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I would check that bleed line I spoke about above, also check that the correct AC DELCO stat was used, the correct stat has an unusually long body, then

I would check your coolant for combustion evidence, that would be easier than pressurizing the cylinders. Check NAPA for Balkamp Leak Detector Kit / Engine Block -- Test Tools Inc.,Test for & Locate Combustion Leaks. For $49 you will have your answer yes or no...

http://www.napaonline.com/cgi-bin/ncommerc...6&usrcommgrpid=

post-3-1131979916_thumb.jpg

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