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We are lookign at pruchasing a 1999 Cadillac Deville from another person who has kept it well maintained. It has 95,000 miles. Our mechanic told us he had heard there had been problems with this model with the engine having to be replaced around 125,000 miles at a cost of $6,000-$8,000. Our present 1994 cadillac has 350,000 miles, no engine problems (not northstar). Has anyone else heard of problems with the northstar engine in later models? Thank you!
 

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1999 White Diamond ETC
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If the cooling system has been maintained and the car has never overheated--there are no inherent problems with the Northstar.

It's an aluminum engine so overheating it can toast the head gaskets and headbolts.

There are plenty of older Northstars on the road, especially on DeVilles... look on the highway, or at the grocery parking lot--many are high mileage.

My mechanic said he's worked on at least 5 that have over 300,000 miles and the only maintenance was cooling system and changing the oil.
 

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I agree, it is a fine car and engine if you keep up with the cooling system and change oil. I would keep the info center on coolant temp and watch it all the time. Mine normally runs 195F-210F. Fans kick on at 222F unless A/C is on then fans will run. Computer on car won't tell you its overheated until around 260F.

Personally, I think with the aluminum engine that is to high. If I got to 245-250F I would pull over and turn off engine to cool it down then look for any problem. Because once the aluminum engine gets to hot, its probably too late for your head gaskets.

Here is where some people will disagree with me: I say use a synthetic oil like Mobil 1. Why? Less friction means less heat and that can only help the cooling system cool the engine and the oil itself will help with engine cooling. Others will probably tell you that synthetic oil is a waste of dollars...I say, you decide.
 

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bubba67801 said:
Here is where some people will disagree with me: I say use a synthetic oil like Mobil 1. Why? Less friction means less heat and that can only help the cooling system cool the engine and the oil itself will help with engine cooling. Others will probably tell you that synthetic oil is a waste of dollars...I say, you decide.
Sounds good at least in theory. I wonder how much cooler it would run though? I was putting in the Valvoline Synthetic Max Life in mine (75K and over), until I read on the forum that synthetic was unnecessary, and not reccomended for oil seepage.

I used to lose more oil then, but I also had an oil cooler line that was leaky. Now the bottom of the engine is "relatively" dry... no leak... but it is moist. I usually have to add a quart between oil changes (per the monitor which run around every 7K miles).

I'll try synthetic again, for experimental reasons (keeping an eye on temperature). Would a free-er breathing exhaust help keep engine temperature down? I'm looking for excuses to get more sound.
 

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mtflight said:
<snip> Would a free-er breathing exhaust help keep engine temperature down? I'm looking for excuses to get more sound.
It should, as it would create less back pressure. The only thing I would worry about in doing so would be if your state has emission standards and inspections that you do it in a way that you still are able to pass emissions testings.
 

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1996 Cadillac Deville, 2004 Cadillac DTS, 2011 CTS AWD Coupe
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So would you say my 96 deville is toast because it over heated? It happened about 3 months ago and nothing seems wrong- what do you think?
 

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Depends on how badly it overheated. If it is running fine and is not overheating or loosing coolant, your probably ok.
 

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1999 Deville
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My 99 is at the dealer right now to get new head gaskets. They thought the original leak was the water pump and crossover gaskets. The next day, coolant level was low, again. Next day, complete meltdown; coolant level dropped so fast, the check coolant level message didn't even appear, but it did tell me to stop the engine and change the oil.
so, I fried it. Dealer is repairing for free, since I haven't had the car for a week when the leak started. We're still wondering what the original source of the coolant leak was. Maybe another part of the head gaskets. He tells me they lift it, drop the front sub-frame, and pull the engine/trans from underneath - a $2k job. My deductible=$100, so with 80k miles, close enough for a coolant replacement and was time for an oil change anyways.
I drive 125 miles a day for work, so we'll know right away if the leak is fixed once I get it back. They gave me an '03 Seville as a loaner, which I've had for a week already, but I like my Deville better.
 

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I highly doubt the synthetic oil will lower the temp of the engine.

Seeing how the radiator cools the engine along with the thermostat, either way you will run at 220 no matter what. My car runs at 220 in -20* and at 220 in 110* in the summer. The cooling system controls the temp, so theres no way oil will keep it cooler. Even if it did, the thermostat would stay closed and heat it up anyway!!!!

Also, even if it were true, you dont want your car running at a lower temp, this causes poor gas milage and other abnormal wear. Just ask some guys that replaced their thermostat with a 165* one and have a computer car or truck, IE. chevy 350.
 

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cl1986 said:
I highly doubt the synthetic oil will lower the temp of the engine.

Seeing how the radiator cools the engine along with the thermostat, either way you will run at 220 no matter what. My car runs at 220 in -20* and at 220 in 110* in the summer. The cooling system controls the temp, so theres no way oil will keep it cooler. Even if it did, the thermostat would stay closed and heat it up anyway!!!!

Also, even if it were true, you dont want your car running at a lower temp, this causes poor gas milage and other abnormal wear. Just ask some guys that replaced their thermostat with a 165* one and have a computer car or truck, IE. chevy 350.
Good observations.

I was going to add a quart of synthetic, but it's very hard to justify the price difference. I'll stick to my Mobil 5000.
 

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Good evening Debbouk,

I have recently purchased a 1999 Cadillac Deville. I was warned that the Engine will blow a head gasket. Well they were right. Due to the heads being aluminum and the bolts that hold the head in are steel, the threads on the heads give way and you blow a gasket. I was told that is the only issue with the Northstar motors. Now while taking my engine apart, my mechanic showed me the inside of my engine. He stated it was a very clean engine and shows that it was well taken care of and I should not have ANY more problems. I know I am not a mechanic and don’t know too much, but I thought I would share with you the problem I encountered. I hope all works out for you.
 

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This is an ancient thread.

Also not all Northstars blow their head gaskets / lose head bolt clamping force. The "root cause" of a failed one is still not very clear, and there are still plenty on the road with factory head bolts/gaskets.
 
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