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97 Deville Overheated!!!


PAUL T

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My 97 Deville with 183,000 miles overheated today. I have had a leak in the surge tank for a few months now. I had been topping the antifreeze (50/50) ocassionally and monitoring the coolant temperature. I had the surge tank out and checked it for cracks but I could not find any. I suspected the line from the surge tank to the "T" and replaced that, but that was not it either. I could see that the coolant was leaking from somewhere underneath the surge tank but not the bottom hose connection. The temperature had been running around normal until today, then all hell broke loose and temperature started running about 230 to 260. I stopped it and let it cool down and added some more coolant while at idle. While at idle, after adding coolant, air in the system was causing coolant to spew. I let it cool down more and added some more coolant and headed for home. About 8 miles down the road It started getting hot again and even steam came out of the air ducts in the car. I am hoping the heater core did not blow. I finally pulled over and called the tow truck to come and pick it up. After I got it home I pulled the hose at the top of the surge tank coming from the water pump to see if it peed antifreeze while the car was running and it did not. So I am suspecting a plugged purge line. Should I replace the thermostat while I am at it? What else should I look at? I am not ready to look for pulled head bolts yet. I have had a squeak from the water pump belt area. Should I replace the water pump too?

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I think I just found my problem. I went to blow through the purge line and it was open, so I decided to check the waterpump pulley tensioner and it was froze. I got a wrench and worked it loose then I started up the engine and smoke started coming out from the waterpump belt area under the shroud. I shut the engine off and removed the shroud and the tensioner pulley just fell apart and the belt was shredded. I am suspecting that the belt tensioner froze in a position that allowed the belt to rotate around the bad pulley not alowing it to rotate the waterpump fast enough or not at all causing it to overheat. I am hoping it can be that simple, we will see.

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Well, that will certainly do it. Occam's Razor says that the simplest explanation of something is usually the most likely one, so you are likely good.

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-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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Just ordered new pulley and 2 belts ($0.71 ea. clearence) for $33 total from Rockauto. I will update when they are installed.

Edited by PAUL T
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Steam from the vents would point to a heater core that has failed or is about to fail. It looks like you found the cause of the overheating issue with the water pump belt tensioner.

Unless the water pump is leaking out of the weep hole, I wouldn't replace it.

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

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I would say the heatercore has failed also.

I would think the coolant you saw coming from the surge tank would be the overpressure relief. There is a hose that runs from the top of the tank by the cap and ends between the engine and body.

Gotta love a good deal. Good luck to you

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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I am a little worried about the heater core. I am hoping the steam from the heater core was at the hose connections to the core blowing into the box or being sucked in from under the hood. I am also getting the change oil message. I checked the oil and it looks and smells o.k., should I change it also it was not very old, I think it was on 70% before the overheating.

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I am a little worried about the heater core. I am hoping the steam from the heater core was at the hose connections to the core blowing into the box or being sucked in from under the hood. I am also getting the change oil message. I checked the oil and it looks and smells o.k., should I change it also it was not very old, I think it was on 70% before the overheating.

Change the engine oil... If it went into limp home mode when it overheated, it will rapidly degrade the engine oil - if the system says to change the engine oil, then change the engine oil.

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

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When the engine goes int overheated mode it sets the oil monitor to zero.

Heatercore is not bad at all to change on these. I have a few writeups with pictures for both dual zone, and single climate control setups

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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I have my old 94 Concours to draw parts from if I need a heater core, but I looked at Rockauto and heater cores run from $21 to $32.

Buy a new one... it isn't worth saving 20/30 bucks and put in an old heater core that might very well fail shortly.

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not only that but disturbing the connections to the old one may cause it to leak also. Get the one without the plastic side tanks if you can help it

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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Well, I got the tensioner pulley and belt on and all seems to be working properly. Bad news is that when I refilled the system with 50/50 antifreeze I had a puddle in the passenger floor board. I guess the heater core is shot. I will have to study up on changing it. I know the connections where the core and heater hoses come together don't look like fun in trying to get it back together. I will post back when I get it done.

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  • 4 weeks later...

Old heater core had a busted place in the plastic end. Got the new aluminum heater core in today and all seems well, no leaks in the passenger floor and none at the firewall. But, my surge tank is still leaking from underneath. I had it out today but I just can not find the crack. All the hoses seem not to be leaking, but there is coolant coming from under the surge tank, not in the hose connection area. It seems to be running down under the battery. I guess it is time for a new surge tank. Tune in later.

Edited by PAUL T
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very good call on the heatercore. very common problem with the plastic tanks on them. they crack right where the neck attaches.

as for the surge tank it may be a pressure leak and is not noticeable til it builds heat and pressure

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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Well I took it on a 30 mile test and it done fine until the last 2 miles. Temperature had been running between 199 & 206. I had not noticed any leaking at the 3 places I stopped, but I did not have the cap on tight. The last mile it leaked antifreeze out the loose cap as the temperature kept climbing until I shut it off. After it cooled some, I started it up and checked the purge line into the top of the tank and it was peeing antifreeze as it should. I also checked to make sure the waterpump belt was turning and it was. I am suspecting the thermostat sticking now. I am going to take it out and see if that makes a difference. I also have a guy checking on a used surge tank for me. I will get it fixed up soon hopefully.

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Taking out the thermostat can hide symptoms of head leakage and thus may not be conclusive. If you want to try a net thermostat then this will eliminate a sticking thermostat. Or you can have your coolant checked for combustion products and eliminate head leakage.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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Forget the thermostat replacement - check the coolant for combustion gas with the kit from Autozone. If anything, it will rule out a headgasket issue.

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

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Got a surge tank, and thermostat coming. After reflecting on why it overheated I am just wondering if having the cap loose may have been what caused all my coolant to boil out last time.

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Leaving the cap loose would cause it to not build pressure and puke the coolant. Have you tested for combustion gasses in the coolant?

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

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Paul,

We are trying to help you on this forum. You may be throwing parts into this car, and a simple combustion gas test on your coolant will be very helpful. The testing tool is rented from say autozone, and the fluid is purchased. This test will tell us if your car has the very common head gasket breach.

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I understand you are just trying to help and I appreciate it. I have went through the pulled headbolts before with my 94 Concours and it's a parts car for my 97 now. I am not ready to acknowledge defeat just yet. I do not even know if our local Advance auto parts place even rents the testing tool out. I have parts coming that will put my cooling system back to original shape with no leaks whether coolant or pressure, if it still overheats then I will check on getting a tester to confirm pulled headbolts. In the mean time bear with me and I will let you know what the outcome is. I have been a regular on this forum for many years and If it was not for the Guru I probably would have swore off Cadillacs a long time ago after having an oil leak in my 94 Concours. After learning a great deal from him I began to repect the engineering that was put into a Caddy and grew to love the Northstar engine.

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