Help My 1999 Cadillac Deville Overheats!!!! - Cadillac Forum - Enthusiast forums for Cadillac Owners

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Old 04-18-2009, 03:46 PM
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Unhappy Help My 1999 Cadillac Deville Overheats!!!!

Can anyone help please!!!!

My 99 Deville keeps overheating.No sooner than i get out of my driveway the temp goes to 180 in a matter of seconds. by the time i reach the end of the block its almost on 266 and ready to shut off. its not a blown head gasket, radiator,or thermostat.replaced radiator,took thermostat out,bought a new waterpump, coolant system etc. Cadillac dealer got about $1014.00 out of me. i dont know whats going on but its stressing the hell out of me.I do know that my heatercore is bad. i figured i could drive on it til i could afford to replace it. drivers side floor it wet from time to time and when the dash suggest cars overheating&idle engine, i take the radiator cap off, antifreeze shoots out and it isnt even hot. when i shut the car off i hear a bubbling sound and cold air blows thru my vents when i try to cut on the heat.could the heater core be the source of my problem?

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Old 04-18-2009, 04:54 PM
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If you engine is overheating and yet the coolant isn't hot.. You have a circulation problem. either your water pump is bad or there is an air pocket caught in the cooling system somewhere.

You say u have a new water pump so that leaves air pockets.

I would drain and refill the cooling system adding 1/4 to 1/2 gal at a time and waiting a 2 or 3 mins between adding. It will take a long time, but it will give time for the air to work its way back to the top of the radiator. Also check your owners manual and see if there are any high spots in the cooling system the require venting... though generally in cars the top of the radiator is the highest point.

Adding coolant too fast traps air pockets/bubbles in the system.. a water pump can't pump air. As a matter of fact I would bet money this is what your problem is.

If that is not it, I would guess that the leak in your heater core is somehow sucking air into the system?

Also be sure it is you heater core that is leaking and not your evaporator... smell the damp spot where it leaks, if it small like nothing or moldy carpet than it is mostly water from your evap. If is smell sweet like antifreeze then it is the heater core.

Last edited by Texan4Life; 04-18-2009 at 05:07 PM. Reason: edited
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Old 04-19-2009, 12:31 AM
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Overheating with cold coolant?

coolant is either not moving at all (pump, air) or it is moving on the pre-thermostat circuit and never reached the radiator (stat, hoses, blocked passage).

possibilities: pump impeller has failed or it is backwards, thermostat is jammed or installed BACKWARDS, air in the system creates pump cavitation, passages are plugged.

on the pump .. we have several incidents where a refurbished pump had the impeller installed backwards. have not seen that in new pumps.

heater core .. fix it ASAP or bypass it and avoid more damage.

you wouldnt have a practical jokes neighbor that would stuff a potato in a rad hose, would you?

did you read our FAQ on overheating?

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Old 08-23-2011, 10:39 PM
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I have a 99 deville. Replaced the radiator, water pump, res cap, hoses,thermostat, heater core, and still overheated. It idled fine after installing the new heater core. At idle it reached 213 and stayed fairly steady. I gave it some trottle. Got up to 239, then dropped to 217. Steady at 217 I took it for a ride. Got about a half mile and 260 degrees. Turned around coasted home. It reached 266 before I shut the. Engine off. Coolant coming out of the overflow and steam from the overheated coolant. Any suggestions? All gaskets check out in good working condition. Was tested.
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Old 08-24-2011, 11:50 PM
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with all that replaced and still over heating sound like an internal gasket issue. the coolant system self bleeds itself of any air. if there is bubling then there is air getting into the system. unless of course the coolant to water ratio is not right 50/50 or 60/40 if you live in some extreme cold weather areas. You said it was tested . what method was used to test for head gasket issues. ive been through this so im positive you got something worse going on if you went out and replaced the cooling system components. is white smoke of any amount comming out the tail pipe when this happens? let us know what you come up with.
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Old 08-25-2011, 09:52 PM
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Default overheating

Did you get your problem sorted yet? I'd like to know what it was or is. I've played with a lot of small block conversions in S10's and love trucks and have found there are pumps that run this way and pumps that run that way. Serp belt pumps run the opposite direction than a v belt so, you said the dealer did the work?? other than that I'd say you have a blockedge somewhere. I can't imagine an air pocket being your problem. and head gaskets can blow between cylinders and to water passages and in this case the antifreeze will go out the tailpipe.
Anyway let us know whats up with ya.

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Old 12-21-2012, 08:49 PM
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Old 12-22-2012, 07:52 AM
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Default Over heating issue

The most common problem is a head gasket leak northstar engine well known for this most likely threads will pull out of block but can be repaired best way to diagnose is with a Head Gasket Leak Detection Tool that can be purchased from a tool distributor like snap on I know this post is old but may help others.
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Old 08-04-2013, 05:46 PM
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Default 99 Deville

Your heater core is right under the passengers feet. Ill put money on it your heater core is cracking or cracked on the plastic part of the heater core it explanes why your floor is wet and air is getting in the cooling system causing the bubbling. I just replaced mine and it was broke on the plastic
it happened on the hwy passing a car.
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