97 Seville cooling problems
 

OK...YES...I have high miles at 157K. This thing runs great! However; last year, it developed an instant overheating condition. It went from running fine to "STOP MOTOR"! I have replaced the Thermostat, bypassed the Heater Core, replaced the Radiator and Hose Clamps. I have NO LEAKS. When it was at the dealership last year before I parked it for the winter, they said they couldn't find out what the problem was and the Heads were fine. I have wondered how you test all the relays on the cooling fans? I know there are supposedly 4, but if the fans are not BOTH running early enough, can these be tweeked like say putting a quicker opening thermostat...say 180 degrees? You would think the dealership, after charging for analysis and actually driving the car for 3 days, would also have records of what they performed. They DO NOT! My next move is to flush and replace the Cooling fluid with a 60/40 mix and add a supplement "Water wetter". I have been told this alows the Coolant to keep the motor up to 10 degrees cooler. Does it sound like I'm on the right track here?

Try the Cap.
 

Have you tried replacing the radiator CAP? They are known to fail.

when was the last time the coolant was even changed? also are you losing oil or noticing the coolant to look sludgy? check to see if it is wet around the cap this will tell you that you are losing coolant.

need details ..

low coolant?

overheat when ?



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No I have not. I would be interested to know how the cap would prevent the engine from cooling properly though.

Here's all I have done: I have replaced the Water pump (although a few years ago), the Cylinders all check out with excellent pressure, there is no water in the oil, there is no visible smoke out of the tailpipe, there is no sludge or thickening of the Coolant and it has been changed twice properly in the past year. I run a 60/40 mix with a "water wetter" supplement. There are NO leaks on any hoses or fittings. The only thing I have done recently different is bypass the Heater Core. All the relays are working properly and BOTH fans are coming on quickly. Radiator has been replaced as well. Here's my assessment: I believe the Dealership dropped the ball. When I asked them to check the Head Gasket, I don't think they did. Whatever test they said they performed wasn't a good one. The pressure is increasing as it runs. When I open the cap, the back pressure in the system forces out coolant. I think more than it should. It leads me to believe the Exhaust Port is leaking gas into the water port through the Head Gasket, heating up the water and creating more pressure in the system. The Cap does open up when the temp peeks over $250 and it starts blowing water through the overflow tube. If there is any other suggestions, I would really like to hear them. If it is the Head Gasket, as I believe, I have been told the left bank is notorious for the Bolts backing out and when you thread the bolts out, it likes to take the threads with them. Also...i'm told the motor has to be pulled in order to do the head work. I am a seasoned motor-head. I'm actually more at home on an 8K HP NHRA motor than this Northstar. Great Motor...strong, runs without a tick or a knock and I also change the oil every 4000 miles. Am I screwed here guys? I hate to think my car is just a huge paperweight now.

Quick thought guys: If I in fact find the Motor to have this slight Head Gasket leak, and I'm being told by Dealerships that it will cost as much as $3000.00 to fix, given the car is in good shape with 157K miles...what would you consider listing it for or would you just dump it? It burns a little oil, but no more than expected. dc

by the way for stealth...it starts and idles great, drives for about 30 to 45 minutes or so, then starts to overheat quickly. weather isn't a factor...cold or hot, same time frame. coolant was again 60/40 mix with supplement and bottle water. I may flush 1 more time and do it again just to be sure its not cavatation or air pocket. I do get a small air bubble that comes up every 5 seconds or so when i'm idling with the cap off. I wanted to see if i had a lot of air going through system. is this any more than normal?

Back to the cap?
 

Picture this scene-- If the cap does not keep the proper pressure the system overheats and the coolant goes into the overflow tank. You open the hood and see there's no leak: you have your coolant still. The engine cools off some and the cycle starts all over again. If the cap does its job then there will be no overheating unless there's a leak somewhere (or the pump has failed) and the coolant level drops. It's an easy test to check the cap.Cheap too.
Also, if you bypass the heatercore you make the coolant capacity that much less by not allowing coolant to circulate through the core. Doesn't that make sense or am I taking a simplistic approach?

Got it...how about this:
 

Cap is working good. BUT..I am losing coolant. I can drive for about 30 minutes or so under normal conditions in the country, and it will then go quickly to the RED and overheat. When I take off the Cap after it cools down some, there is a LOT of pressure and it can be as low as a Gallon and a half on Coolant. I do understand less Coolant by bypassing the Heater Core. But that is not the cause of this problem. I can fix everything, replace heater core, new hoses, no leaks...and it will still overheat. I am 90% SURE, its a Head Gasket blown between an exhaust port and a water port. That would lead to the increase in pressure within the system and it superheating the water to push the Cap and blow HOT Water through the resevoir hose. Recently, I also replaced the Power Steering Cooling Coil. Here's my true point: I have no problem working on the vehicle. I'm no Certified Caddie Master Mechanic, but I can break down a Motor and rebuild it in the course of a long day. I have one of 2 solutions: pull the Motor and replace the Head Gaskets, make sure the Head isn't warped, HOPE the block has not incurred stress cracks (which i believe it has not), and HOPE the threads don't strip out when I retorque the Head Bolts. Lot of work, but not a lot of money. #2: I replace the Motor. Obviously, this is also a lot of work and a LOT more money, and: if I buy a used Motor with say, less than 50K miles, I gotta HOPE there is nothing wrong with it. YIPPEE! SO...this is my dillema. Either way, I like the car. It looks great. It drives great. The Interior is very clean, the Air blows Cold (when it can), and its simply a nice ride. I hate to think its now just scrap because of an Engine failure that CAN'T be fixed because of engineering snafu's. What can I sell it for and how much can I get for it? That may be my next task. Anyone with a 97 Northstar Motor in good shape could get a Hell of a Deal on a car right now. Thanks for the input SKYZZICS.

1997 engine, probably running on original coolant when the headgasket failed.
yes it happens, more often that we like.

FAQ has details on such events.


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if your looking to sell the car you would get more by selling the parts off it on ebay. The whole car is really not worth much to people now days since we scrap cars and buy another one. Or people need a part off it and can get used parts cheaper and easier. now if you get a used engine most time they will pressure test it and thats it, but you never know the condition of the gaskets.

I bought my 98 seville with a used engine that was put in with 60k and 5k later the gaskets went out and i experienced all the symptoms you did. My bill was $2800 at the dealer. Nobody in my area would even look at it. One guy hung up on me as soon as i said northstar no joke. i called back cuz i thought he accidently hung up and he said He worked for GM when they came out with this engine and he quit working on them after dealing with all the problems. He said thats all he did at the dealership was tear apart thes engines because of this. The engine its self was in good shape but was never able to be assembled together and hold up for long. He stated that its not worth the customers money or mechanics time to repair these engines. He also says there is a 60% fail rate when these engines ared repaired. so you are basicly in a pickle if you want to keep this car running. but you can always find another cady if you like these cars.

the real sad thing about all this is that the engine is fine .. these Northstars will go 300,000 to 400,000 miles w/o a glitch if and only IF, the coolant is changed out every TWO YEARS. the engines are awesome in performance and durability .. the engines were designed to last longer than the car itself .. they were not designed to be overhauled & there you have the problem with mechanics .. but the designers never imagined what would happen next.

the problem is that the EPA wont allow GM to call for a coolant change before 10 years (or is 5?) !
Again, our go'ol govt telling us they are smarter than us. more govt anyone?

if you dont know already, every aluminum engine out there is being afflicted by the same issues of coolant protection depletion. and like GM, no one is stepping forward and letting the owners know. the makers just deal with it within the warranties when things go bad. coolant depletion takes place on a time basis, not mileage ! 5 years from new and two years thereafter is what we know!

sounds like the problem is slight head gasket leak...the problem will continue to get worse.