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George H.
George H., ASE Certified Technician
Category: Cadillac
Satisfied Customers: 18830
Experience:  ASE Master Tech 15+ Years
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99 Deville: trip..fluids..It has been slowly loosing coolant

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99 Deville, Coolant Disappears??

The other day I and three others started a small trip. I checked the fluids before I left - toping off the coolant. It has been slowly loosing coolant for sometime now. My mechanic can't find anthing wrong.

It was in the low nighties, the air was on, life was good. we got around 30 miles and the display message said that it was overheating, then the AC was turning off, then turning on 'idle'. I idled to a jiffy lube, the coolant was bone dry. We found that the cap wasn't holding pressure because some pieces of rubber were missing. The only thing they had was a '16' (instead of a 15) - they said it would be ok. (my mechanic concurred later). Thinking that was the problem, got down the road around 20 miles and it was bone dry again. I had it towed to my mechanic.

They did a 'Block Test (chemical test), Cylinder Leakage Test, put it under pressure and looked for internal and external cooling system leaks They let it sit running for a couple of hours in the sun in the middle of the day to see if they could get a clue. Nothing.

They had also put a couple of bottles of 'cactus juice' something or other, to plug potential cracks in either the engine block or heads (can't recall which).

Any ideas, short of trading it in for something that doesn't have a northstar engine?

Hello I will help you with your question,


Your northstar is certainly a victim of the design flaw that allows the cylinder head bolts to tear out of the block from thermal expansion despite the block test results.


This means you are burning the coolant and the problem has gotten to the point that it can no longer be operated for any length of time on the road.


The acceleration causes the cylinder pressures to raise so the bolts pull out a little and the head gaskets leak. They go back in place at idle so that is why you can idle for hours but not run down the road.


The sealer will not cure this problem, the only fix is to disassemble the engine and install "Timesert" thread repair inserts or as you say "sell it and buy a non northstar engine"


Sorry for the bad news but if you google northstar head gasket problems you will find thousands of posts on this subject


Please let me know what I can do to help you


Thank you



Customer: replied 7 years ago.
You mention "disassemble the engine and install "Timesert" thread repair inserts". What's a "Timesert' thread repair insert? generally speaking (I know I can't hold you to it ;^) - what would be the cost of having some who knows what they're doing, get it done in the midwest?

The timeserts are installed in the holes in the block that the head bolts are threaded into. The cost to do this is more than installing a remanufactured engine like a Jasper (3 yr 100,000 mile warranty) which runs about $7000 installed.


In the case of installing the timeserts the engine should be rebuilt as all the labor is in the disassembly and reassembly so while it is apart you should replace all the wear parts. This can be done in the vehicle by just removing the cylinder heads drilling and installing the inserts and reassembling but you still have a bottom end that may fail and you are installing new gaskets and seals forn the upper. I would not recommend this route if you plan on keeping the car for many more years. You still have the issue of the solenoids in the transmission that overheat and fail so you have to make a decision of how much you are willing to put into this vehicle vs a new car payment or a newer used car.


Once again I am sorry to hand you this news but please spend a little time with google and see how widespread the problem is.


Let me know what I can do to help





George H. and other Cadillac Specialists are ready to help you
Customer: replied 7 years ago.
Did they get the design fixed so this won't be a problem with newer models?

From 2004-5 on up there is a better design so after that the engine will not have this problem but you have to understand that GM no longer builds cars/engines to last. They believe that every five years you need to buy a new car and they engineer them to last the length of the warranty. With all the bells and whistles they are installing you have lots of electrical/electronic failures and many of the features don't last as long as designed. The basic (expensive) systems of the vehicles last now but the switch gear, window regulator, backup sensors, navigation systems etc do not do well in the automotive enviorment.


Please let me know if you have further questions about this


Thank you