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97 Cadillac Deville overheating - help is appreciated


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xlaxplaya
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Mar 18, 2012, 7:41 PM

Post #1 of 9 (5266 views)
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1997 Cadillac Deville, 4.6L V8
66,000 miles

I recently got my hands on a 97 Deville in excellent condition, except for overheating issues. At first, I feared a blown head gasket or worse, but I did a pressure test and a block test, and both came back normal.

Later, I noticed that the radiator fans don't turn on, even when the coolant gets up to 225 degrees (I'm afraid to run it any hotter than that). However, the fans WILL turn on when the AC is on, and the coolant quickly goes back down to around 200 degrees. I've checked all the fan relays, and they're fine. The only other thing I can think of doing is replacing the coolant temperature sensor, but that doesn't make much sense to me. The computer is displaying the temperature on the dash; it's just not kicking the fans on unless the AC is turned on. I used a friend's scanner, and it's not throwing any error codes, and I'm getting no warning lights on the dash display.

I'm kind of at a loss here. I can't figure out what the problem is. Some questions, I hope somebody can answer them:

1. Does anybody know the temperature at which the fans are supposed to come on?

2. Is there more than one coolant temperature sensor (one to switch the fans on, and one to talk to the computer)?

3. Is there anything other than the relays and the temperature sensor that could be causing this?


Hammer Time
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Mar 18, 2012, 7:52 PM

Post #2 of 9 (5257 views)
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Re: 97 Cadillac Deville overheating - help is appreciated [In reply to] Sign In

Your problem is that you don't have a problem.

It is normal for those fans to come on at 226 deg or higher. They are intentionally programmed that way.




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xlaxplaya
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Mar 18, 2012, 8:03 PM

Post #3 of 9 (5249 views)
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According to the manual, normal operating temp is between 180 and 200 degrees. But thanks for the tip, I'll take it for a drive to see if I can get it above 230, and see if the fans kick on then.


Hammer Time
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Mar 18, 2012, 8:09 PM

Post #4 of 9 (5243 views)
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You'll never get it that high with the car moving. The thermostat is 195 degree and it will run around 200 with the car moving but with the car stopped, the fan will let it get hotter before coming on. That's normal and done for emissions reasons.




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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



xlaxplaya
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Mar 18, 2012, 8:56 PM

Post #5 of 9 (5216 views)
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Thanks, you're right. The fans kick on around 222 degrees. I just took it for a drive and it looks like I've got bigger problems. It overheats very quickly at high RPM's (going up hills) and acts just like the gasket is blown, but as I said, I used both a pressure test and a block test, and both indicated no gasket/head leaking. But I'll make a new thread; the title issue is null.


Hammer Time
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Mar 18, 2012, 9:02 PM

Post #6 of 9 (5211 views)
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Neither of those tests will tell you anything conclusively. These engines are notorious for the head bolts pulling the threads right out of the block. The only real accurate test is to use an exhaust gas analyzer over the radiator cap to sniff for hydrocarbons.

If it's consuming coolant and/or building pressure very quickly, that's likely the problem. If it's getting hot without first losing coolant, then it's likely a bad radiator.




~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



xlaxplaya
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Mar 18, 2012, 9:55 PM

Post #7 of 9 (5196 views)
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That's what I meant by "block test"; a hydrocarbons test. Should have been more specific. Actually, it looks like it might have just been a faulty radiator cap. I pressure tested the cap, and it looks like it purges at only 5psi, which could lower the coolant level, which could cause it to overheat. I'm planning on flushing the radiator tomorrow and replacing the cap, and I'll see what happens then.


Hammer Time
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Mar 18, 2012, 9:59 PM

Post #8 of 9 (5192 views)
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Quote
That's what I meant by "block test"; a hydrocarbons test


You were talking about an inexpensive chemical test using blue fluid which can be very unreliable and I'm talking about a $10,000 4 gas exhaust analyzer. Not the same




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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



xlaxplaya
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Mar 18, 2012, 10:01 PM

Post #9 of 9 (5188 views)
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Oh good god. That sounds fun. Okay, I'm gonna see what happens tomorrow and make a decision from there. Thanks for your help.




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