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1998 Deville Over Heats, Running AC Cools Engine Temp


amber

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Our 1998 Cadillac Deville overheated while on vacation in Idaho going up a steep mountain road and we had it towed to the Cadillac Dealer. They said we needed a new radiator although ours was only 1 1/2 years old. It may have been installed incorrectly by another mechanic. Anyway, after $1600 including a new radiator, thermostat, water pump "kit" and new gasket on the bypass at the water pump, we got the car back. It ran fine for the 300 mile drive home and for about one month. I watch the temperature every time I drive it. After the new radiator the temperature would occasionally climb to 222 when driving at lower speeds, (i.e. under 60 mph) or if running stopped for prolonged periods of time (say 10-15 minutes in the ferry line). Then fans must be kicking on and it would cool to 196. At freeway speeds pretty well ran at 196-201.

About a week ago in stop and go traffic on the freeway it over heated again (pulled into the right lane when the temp was at 220 and it spiked to 240 within seconds by the time I could safely pull over). After waiting on the shoulder for 40 minutes to let it cool, it ran fine. It ran fine for a week and now after running about 10 minutes the temperature starts to climb from the 196 then 201 then 212 and so on until it over heats, even at freeway speeds.

Have driven it only on short trips of a mile or less but had to drive it yesterday to get studded snow tires off. After about 5 minutes temperature started to climt from 199, 201, 212, 217 so we tried turning on the AC to the coldest temperature and fan on high, (saw this in other posts) . It cooled from about 222 to 196 (*with in 2 minutes.) The driver side two vents (left most and left center vent) blew cold air and the right most vent and right center vent blew very hot air. When it cooled to 196 we turned off the AC and it started to heat up again until we turned AC again.

I asked the Dealer in Idaho if we could have a blown head gasket and they said they did not think so. No while smoke, no coolant in the oil etc. I am not sure why they did not run the test described on this site for exhaust gasses in the coolant. Is cooling off when the AC is running and blowing very hot air into the car on one side a symptom of a blow head gasket or a clog in the cooling system? Saw a post that if the tablets are put into the surge tank this can clog the cooling system which I suppose the dealer may have done. I would believe a Cadillac dealer would know better. The car has 94,000 miles.

Any ideas would be helpful as I am tired taking it to mechanics, including the dealer that don’t seem to know what they are doing. Thank you.

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It sounds like the cooling fans are not operating properly. I doubt you needed a new radiator but that's the part that is usually thrown at an overheating problem first followed by a thermostat and then a water pump.

Let the car idle in the driveway and monitor the coolant temp. while observing the cooling fans. Note the temperature at which they turn on or if they do not turn on.

When the A/C is turned on, it forces one of the cooling fans to run so that exlains why the temperature dropped.

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

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The temperature pattern you described looks normal to me. What do you mean when you say the car overheated? Some of dealers are jokes. Charging $1,600 for radiator replacement... An aftermarket radiator is about $150 and is as good as OEM one. The installation is 1.5 hour job.

The saddest thing in life is wasted talent

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The temperature pattern you described looks normal to me. What do you mean when you say the car overheated? Some of dealers are jokes. Charging $1,600 for radiator replacement... An aftermarket radiator is about $150 and is as good as OEM one. The installation is 1.5 hour job.
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The temperature pattern you described looks normal to me. What do you mean when you say the car overheated? Some of dealers are jokes. Charging $1,600 for radiator replacement... An aftermarket radiator is about $150 and is as good as OEM one. The installation is 1.5 hour job.

The car definately over heats, my husband and son were not watching the temp last week and it got over 248 and then displayed "Idle Engine" and then I believe something about auto shut down before they got pulled over. I watch the temp very closely and and start thinking about pulling over at abourt 228 as once it gets over 228, it gets to 240 or above with in a minute or so.

After we had the first radiator put in about 1 1/2 years ago we had a clogged by pass so I know to watch the temp after a radiator change out. Once the bypass problem was resolved and until the problem recently on vacation in Idaho, the car seemed to always run under 212.

I will check the engine temp and watch when the fans kick on at idle. Any ideas why onbe side of the heat vents would blow very, very hot air and the other one normal air conditioned air.

It sounds really weird but could something in the heating/coling ssytem be affected if the climet control switch on the passenger door was hay wire? The know that allows the passenger side to be controlled differently than the driver side? Seems so odd the only the right two vents blow the hot air with the AC on. And this air is very hot, like it you have the heat on full fans and set to 90 degrees.

"

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I agree, Amber. Have the test done. Unfortunately you're symptoms do not look good. Check it out before putting any more money into it. That Idaho dealer sounds like a ripoff artist.

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The temperature pattern you described looks normal to me. What do you mean when you say the car overheated? Some of dealers are jokes. Charging $1,600 for radiator replacement... An aftermarket radiator is about $150 and is as good as OEM one. The installation is 1.5 hour job.

The car definately over heats, my husband and son were not watching the temp last week and it got over 248 and then displayed "Idle Engine" and then I believe something about auto shut down before they got pulled over. I watch the temp very closely and and start thinking about pulling over at abourt 228 as once it gets over 228, it gets to 240 or above with in a minute or so.

After we had the first radiator put in about 1 1/2 years ago we had a clogged by pass so I know to watch the temp after a radiator change out. Once the bypass problem was resolved and until the problem recently on vacation in Idaho, the car seemed to always run under 212.

I will check the engine temp and watch when the fans kick on at idle. Any ideas why onbe side of the heat vents would blow very, very hot air and the other one normal air conditioned air.

It sounds really weird but could something in the heating/coling ssytem be affected if the climet control switch on the passenger door was hay wire? The know that allows the passenger side to be controlled differently than the driver side? Seems so odd the only the right two vents blow the hot air with the AC on. And this air is very hot, like it you have the heat on full fans and set to 90 degrees.

"

No, you appear to be having a problem with your HVAC system, if you retrieved the DTC codes it would show a code, I bet.

Have you checked your purge line to see if it it clear?

I agree with what KHE said that turning on your AC turned your fans on HIGH improving the cooling, and its possible that with the AC off, your fans never come on. At high speed however your fans are not needed as ram air pushes air through the radiator, if anything you would overheat at low speed or sitting still. Turn AC off, idle engine fans should come on about 222 if I recall, but keep an eye out as to what temp they do turn on and let us know

Check your water pump belt for cracking, tension and slipping

There should be a 50/50 coolant to water mix, to prevent boiling make sure that is ok, if it is less than 50/50 it will boil at a lower temp

If you didnt replace the thermostat, I would check that, but I think you said it was replaced

You should check your coolant checked for combustion by products if the above checks out ok

Go to the top of this page click HOW TO, than DTC CODES and follow the instructions for how to pull the computer codes and post them here, this is IMPORTANT

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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