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Coolant Change for 97 DeVille


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Hey All,

I put the car in the shop this morning to have the blower motor replaced, and found that my coolant loss was from a heater hose. Hennessey Cadillac of Gwinnett, Georgia told me the car had blown head gaskets and not to put any more money into the car as it was a loss last week; for those of you who didn't know. Thanks for all the great advice!! It's because of your input that I still have the car, and got a second opinion. :rolleyes::D I told the service man to put six supplement tabs in with the coolant. He said they normally would put three in (Chevrolet Dealership close to work.) there cars but wasn't sure about six. Is six required only because of the NorthStar Engine??? I need to call him to make sure they put six in if so...

Thanks in Advance Again!

Mark :rolleyes:

Oh! Something else. When should the belts be replaced? I have 114.000 miles, and wasn't sure how long they normally last. Plus, I could keep the old belts for an emergency.

Mark McDermott

79 Deville 84,000

97 Deville 279,000 :yupi3ti:

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I think six tabs is the right number to be added if all the coolant is changed. The tabs that I bought at the dealer, came six to a pack. I wonder if the dealer will use distilled water for the proper 50/50 mix.


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I think 3 is correct.

Here is the shop manual warning for the Northstar:


This engine uses DEX-COOL® and GM coolant supplement (sealant) P/N 3634621 specifically designed for use in aluminum engines. Failure to use the engine coolant supplement (sealant) and the approved coolant antifreeze could result in major engine damage. When refilling the cooling system, add three pellets of the engine coolant supplement sealant GM P/N 3634621 to the lower radiator hose.


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Great to hear! I guess Hennessey Cadillac should work on their customer service a little better.

I had my belt replaced at about 80K. You can usually tell by the way the belt looks. If there's a few cracks and it looks worn, I would replace it. It's not that expensive and it will give you piece of mind.

1994 STS Pearl White 260,000 KM (163,000 miles)

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