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David H
David H, Cadillac Technician
Category: Cadillac
Satisfied Customers: 2677
Experience:  18 years cadillac dealer.ase master master certified
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2000 Cadillac Deville. Only overheats under a load, (AC on

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2000 Cadillac Deville. Only overheats under a load, (AC on and driving), Coolant is good, no front end damage, replaced thermostat, water pump, temp sensor, flushed coolant system, made sure the radiator flowed and well as had flow thru the block, no loss of coolant even though after about 5 minutes of driving the check coolant light comes on, no oil in the coolant, no coolant in the oil, and no white smoke out the exhaust, heat works good. I can leave the vehicle idle for ever without it getting overheated, scan tool says between 210-225, i can turn the AC on and the temp fluctuates and hovers around 230, I can drive without the AC on and the temp fluctuates around the 230 mark, but if I turn on the AC, with in 3 minutes its overheating, the engine hot AC off light comes on. What would you suggest?
Submitted: 6 years ago.
Category: Cadillac
Expert:  David H replied 6 years ago.
Make sure both cooling fans are running at high speed with a/c on and engine temp. at 230 deg.The check coolant level light is most likely a failed coolant level sensor in the surge tank.This would require replacing the surge tank.
Customer: replied 6 years ago.
Both fans are working properly, high fans actually come on at 235 and kick back to low around 200
Expert:  David H replied 6 years ago.
Then you may have a small leak from the head gaskets,I have run into this same problem before.The leak can be small enough to only leak under load.This would not show up in the oil or exhaust.I usually run a block test on the cooling system to verify the leak.
Customer: replied 6 years ago.
I did a block test, 4 separate times...the first time it turned yellow right away, and after it cooled some it never turned yellow again. I did add "iron tite" to it today with no avail, do you know of anything "quick fix" other than replacing the head gaskets, bolts, etc.
Expert:  David H replied 6 years ago.

Unfortunately I have not found any quick fix and I do have experience with hundreds of head gasket repairs on Northstar engines.Every time there is a head gasket leak on this engine one or more of the head bolts have pulled the threads from the block.

Customer: replied 6 years ago.
Is this repairable? Is there away to check the bolts? If I pull the spark plugs will I be able to tell which cylinder(s) are leaking? Also, I am a mechanic, ASE Certified, this just didn't act like the typical "head gasket" and I am the only technician at the car lot so its difficult for me to bounce ideas off other techs, and I dont do alot of work on Cadillacs unless its electrical or diagnostics.
Expert:  David H replied 6 years ago.
To repair the block requires a TIME SERT repair kit.You can order this kit know which bolts are pulled I remove the valve covers and apply torque to the bolts to see if they hold.I have always repaired all 20 head bolt threads in the block.Truth is you can replace the engine with a good used rebuilt for almost the same cost as repair.The new engine will come with a warranty so you don't have to risk the block repair.This block repair procedure is difficult and risky,it is not guaranteed to hold.

Edited by David H on 8/5/2010 at 12:10 AM EST
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