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97 Deville Overheated!!!


PAUL T

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Coolant testing is fast, simple, inexpensive, and a negative result rules out head leakage. Since it's easier and cheaper than changing a thermostat, I would do that second, right after checking the bypass for blockage.

That's the perspective of someone who wants to get to the bottom of things as quickly and inexpensively as possible. As an owner, I might want to avoid facing the prospect of the biggest possible problem as long as I could. But doing so will only cost you more time and money.

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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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Everyone has their own way of doing things and I don't expect you to understand my reasoning. I do appreciate your help and your advice has been noted. I will post back when I get things back together.

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Oh, yes, I do understand your reasoning. I had my 1997 ETC for almost 15 years and I did have the dreaded pulled head bolt. And I did everything possible for months before I had a pressure test that told the tale.

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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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I have to admit I would want to know but at the same time I wouldnt want to face the possibility. I have already bought 3 that have had the problem and you can follow the symptoms as it progresses to not being drivable.

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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I did the same thing, and was in denial for months. I was new to Caddyinfo then and less was known about the problem and its causes. But my records shows that I had gone seven years without a coolant change. Coolant testing for combustion products was harder to get then, so I got a pressure test that told the tale. With the engine out, we could see coolant seepage on the rear head at the corner nearest the firewall, showing that it had pulled a head bolt.

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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Update: I got the Surge Tank and new thermostat in and have driven it about 50 miles total and no visible leaks or overheating. I had one scare on a hot day where the temperature went to 232 but after the fans kicked in it went back down to 217. During normal driving the temperature fluctuates from 194 to 205. The real test comes when I get it on the interstate to 70-75 mph. I had to top the coolant off once since refilling the surge tank with coolant after repairs. Wish me luck.

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I agree completely with your trouble shooting methods and the parts that you replaced on your Caddy. I believe that for any proper fix to be done correctly, fix what you KNOW is broken first. Yeah, maybe I would have not replaced the thermostat, but that's about it. Keep an eye on that purge line for a while. Make sure it is flowing well, and if you notice that it CONTINUES to belch air from time to time, expect big trouble. Check your coolant concentration to ensure it is between 50 - 55% coolant. I have a tester, or maybe you can rent one locally.

After about a month (maybe less) without overheating, you may want to do the exhaust gas check on the coolant tank. Just to satisfy yourself.

Never underestimate the amount of a persons greed.

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Make sure that the coolant is at least 50% antifreeze, but not more than 70%. Otherwise you can have coolant loss or even overheating because of excess steam pockets in the head. Pep Boys and other auto parts stores carry antifreeze testers.

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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I used a 50/50 mix for coolant. I have logged about 65 miles of short trips and no problems yet. I have no leaks also. I am doing a 40 mile round trip tonight. I had a spike today while idling in town. Coolant went to 212 while idling, when I started moving again it went back to 194 so it seems to be doing what it is supposed to do. Johnny, I agree with the exhaust gas check later just for peace of mind.

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From what you are posting here, everything looks normal. From the 1997 FSM p. 6-797:

Fans turn on low when the engine is 229 F, OR the transmission is 302 F, OR the A/C is on.
Fans stay on with key off if coolant is 304 F or higher.
Fans go off when engine is 216 F or lower.
Fans go to high if Engine is 234 F OR transmission is 304 F.
Fans drop from High to Low when Coolant is 229 F or lower.

Other tidbits: The thermostat is a 180 F, meaning it starts to open at 180 F. It's placed near the water pump and senses the temperature of the water at the water pump inlet going into the block through the crossover. The ECT sensor is on the head near the crossover, arguably the hottest point in the coolant circuit, and 195 F is about the right temperature when the thermostat is fluttering to keep the water at the water pump just over 180 F.

The 1997 FSM, page 6-196, has a short paragraph on coolant circulation:

Cooling System Circulation

In the Northstar cooling system, the water pump takes coolant from the radiator and passes the coolant through the thermostat on the inlet side of the water pump. The coolant enters the block at the rear of the engine from the water crossover, then the coolant is routed through the cylinder heads back to the water crossover. At this point the coolant has four possible routes:

  • The radiator
  • The bypass
  • The heater core
  • The throttle body heater circuit

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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  • 2 weeks later...

Update: Have put over 500 miles on it since fixing, even on 90+ degree days and no leaks or overheating. I think it is fixed. It even done well at 75 mph on the interstate. Now if I can get to 189,000 miles I will have put 100,000 miles on it, It has 184,000 miles now. Not bad for a car I only paid $4000.00 for. Thanks to everyone for their help and advice I really appreciate it.

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:hatsoff:

I think we can declare victory on this one.

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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Congrats!! Even though it is working good, remember, it's an older car, and opening up the hood every week or so to check fluids / anything loose, or just giving it a sniff goes a great way. I wish you 300k on it.

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