QuestionJust bought a 94 Cadillac Deville Concourse. It has 113,000 miles. I'm not afraid of the miles because my previous experience with Cadillacs is that if they are cared for you can get 200,000 pretty trouble free miles out of them. This one shows all the signs of having had great care. Had an overheating problem on a recent 350 mile trip. Stopped immediately...waited for cool down...refilled with antifreeze. No problems for two days. Then when returning home had the problem again while traveling on an uphill grade. Local mechanic replaced cap and thermostat. Problem persisted. Temperature would vary between 194 and 208 but when pulling the grade again would escalate quickly from 210 to 246. Fans seem to work fine, but coolant would always be low. Mechanic did a "block test" and told me that I need a new engine. Took it to a radiator repair shop (car works fine on level terrain) where they did the same thing and gave me the same answer, need a new engine. They are speculating that the head gasket has a crack that only opens when then the engine is under torque, like the uphill grade, the combustion gases then escape into the coolant which superheats the coolant in seconds and causes the overheating.
Questions: Does that sound like a reasonable diagnosis? The car runs like a dream on level terrain. Could it be something else that we are missing? If the diagnosis is correct should I consider replacing the head gasket and, if necessary, rebuilding the top of the engine? The local mechanic said that this will hardly ever give a good result and he wouldn't guarantee his work. The service manager at the Cadillac dealer says they usually get a good result and he will give a 12 month 12,000 mile guarantee. Or is it best to spend the money on a new engine? Or should I try to sell the car and cut my losses? Is this a common issue with the Northstar engine?
AnswerFOLLOWUP: There is also a STRONG possibility that you have a radiator problem such as a residue buildup at the bottom of the radiator vanes and partially up towards the center of the radiator OR you could have a problem with the lower and middle coolant chambers of the radiator that are collapsing when hot thus restricting the coolant flow.
Just because you can see coolant flowing via the radiator cap acess hole of the UPPER vanes expelling coolant, you CANNOT see what the middle and or BOTTOM vanes are doing.
With 113,000 miles on it and if it were my vehicle and a cylinder air pressure tset revealed no bubbles coming from the radiator, I would opt to remove the old radiator and flush out the system and install a NEW radiator and see if your overheat problem is resolved. This would be warranted ONLY if the cylinder air pressure test proved OK.
Even if you have to do the engine work I would STILL install a NEW radiator. I did NOT say to have your OLD one REBUILT or CLEANED & FLUSHED, I said a NEW RADIATOR as I have seen many radiators that were rebuilt cleaned & flushed that still failed due to weal coolant chamber vanes that collapse shut when the radiator gets HOT.
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I agree with the diagnosis that you got. It is most likely a head gasket(s) problem.
However it is possible that you may have a crak in the head(s) and or in the engine block. This you won't know until the heads are removed and checked.
With 113,000 miles on the engine this is a "toss up" as to what to do.
If you spend the money to pull the heads OFF and they find a crack in the head(s) or in the block or they observe some excessive piston side to side movement in any of the cylinders then your looking at rebuilding your old engine or replacing it with a REBUILT or NEW engine. I do NOT EVER recommend installing a USED JUNK YARD engine as you have NO WAY of knowing how long the engine has been sitting in the JUNK YARD and or it's running condition.
Sure, the JUNK YARD will give you another engine if this USED one is NO GOOD after you install the engine to only find out it's no good, But your STUCK paying for all the labor costs.
I can't make this decision for you, So you can either GAMBLE and pull the heads off and hopefully all that is found wrong is that the head gasket(s) are blown but you could find other problems as well.
If it were my vehicle and I knew the REPAIR HISTORY of the vehicle and the vehicle looks good and everything else runs good, I would OPT to install a new or rebuilt LONG BLOCK.
Then you have the possibility of the transmission going bad within the next 10 to 30 thousand miles.
This is where it becomes complicated in making a decision as IF it were my vehicle, I would be doing all the labor with the engine and trans.
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