Any Cadillac gurus here

[briano]

I'm going to look at a 97 Caddy after work, the guy says there's an issue. First off, I'm a mechanic and know a little bit about what's going on but this is kind of odd. He says the car started this after changing the radiator, it will just all of a sudden peg to HOT and piss coolant out of the overflow, you can pull over and fill the coolant and take right off and it's fine. He says it will do this out of nowhere about every three or four weeks in the summer. Now it hasn't acted up since November. This car is in beautiful condition and I'm looking to buy it for $1000. I really don't think it's a head gasket issue because it can be driven for so long between the overheatings. Anything else you guys can think of. By the way there is 104,000 miles on the car and it is the Northstar engine.

[trike savior]

i have a 97 deville concours and have done a ton of research on the cars and have helped a few family friends when similar things happened on theirs. IT IS THE HEADGASKETS, GUARANTEED. the 4 cam northstar motor is notorious for it. it only has to get hot once and it is done. whatever happened that caused him to change the radiator probably involved an overheat event and that is it. it is very expensive to fix.
they wont leak externally, but internally, causing the cooling system to become pressurized with combustion. this crates air pockets which gives you overheating when driving.

the fix:
what actually happens with these is when it gets hot the aluminum block releases the threads for the head studs. this causes the gasket to leak and in most cases warps the head.
provided you get lucky and the heads do not need to be re-decked. all the old studs need to be removed and the holes re-threaded. there is a new replacement head stud kit that uses coarser tread head studs to keep this from happening again.

so tear down the motor, re-thread block, new studs, new gaskets, and reassemble. this is why every shop quote is $2500 or more. engine has to be removed because the rear cylinder head cannot be removed in car. And on these cars motor comes out from bottom. car has to be lifted off the engine/ trans/ suspension cradle assembly. you must have a lift to do the work

Many people have tried barr's block seal (same company who makes stop leak). If it works, it works for a while and eventually quits.

i got my concours for $2100 (trade in value) with no issues with 89,000 miles. If it is a base model they are worth even less.

I wouldn't pay 500 for it. scrap value or junk yard value is all it is worth. $250-300 tops.

Other common failures: alternators take a beating, being on bottom of motor (idiots). there is a seal in the trans that commonly goes and causes it to loose torque convertor clutch lock up. car still has all gears but no lockup on the convertor makes the gas mileage on the highway go to crap.

these are great cars and i absolutely love mine. but if you are not a mechanic, you might stay away.

the 94-95 look almost exactly the same and have the older bulletproof 4.9 motor. the 4.6 4 cam northstar is in everything, deville, sts, sls, Eldorado, and others i am forgetting from 96-05. it is a wonderful motor, being 4 cam it sings to 7 grand like a beautiful orchestra. 300 horses that will cause you to turn down radio to listen to the motor. but they have some super expensive faults.

[wisconsinite]

I know some caddy stuff, but pretty ignorant on the northstars. Almost sounds like the waterpump is airpocketing occasionally, or maybe a sticky thermostat?
I had a saturn with a bad radiator fan relay, sometimes it worked, sometimes not. Something like that maybe?
Posibly some mystery crud got into the cooling system when the radiator was changed, and is occasionally blocking flow?
Good luck with it, these random problems can be easy fixes or nightmares.

[wisconsinite]

Trike savior and i must have been typing at the same time lol. Good point on the aluminum heads, they hate overheating. Compression slowly pushes out coolant, eventually gets low enough to overheat. Makes sense.

[fabiodriven]

Definitely the head gasket, no question.

[briano]

Trike savior, I've also researched this problem. I just don't understand why it can go for long periods of time and all of a sudden overheat. The guy that owns the car works at a dealership and they have pressure tested and checked for exhaust gasses in the coolant, everything checks out fine. I'm not saying that you're wrong, I thank you for the input, but it just seems strange to me. He has been driving the car all winter now and it's been fine. I really want the car but I guess I should keep looking for something else.

[trike savior]

with how cold it has been over heating is not an issue and that is probably why he is trying to get rid of it before it gets warm out. if he works at a dealership he can do things to make it appear it is not head gaskets, like changing fluid or he is adding enough that you cannot see the combustion contamination. he may have done a leak test but might have done it cold when things are fairly tight.

i can tell you from his asking price he knows what the problem is.

i would say keep looking for a good one. and if you are looking for a 97-99 in particular, get a concours. the base and d'elegance are nice but having split buckets and a center console is way better. and the concours is the only one that gives you an analog cluster with a coolant temp gauge. the other 2 have digital with an overheat light and by the time you notice that little b@$t@rd it is too late.

[fabiodriven]

What probably happened is someone overheated it and caused the head gasket issue or the head gasket let go and they're changing other parts in desperation to try and fix it. I've seen it a hundred times. Regardless of the cause, the issue now is the head gasket without question.

[briano]

Ok, thanks guys. I'm going to keep looking. How about the 2003 and newer, are they any better?

[trike savior]

The newer ones are much improved but as with most new cars the worry becomes the electronics.

[atc007]

I am no help to this thread except when reading the PO 's 1st post I certainly thought air/bleeding problem. But from compression?? Ugly. I have a 06 DTS,cloth roof,,,yes,,factory Caddy cloth roof. Rare car.. 2002 Miles. I bought it to fix up for my Dad , his health declined,and I never got to it. It has a little tiny little lol ,,chip out of the front head where the motor mount mounts. On ANY other engine it wouldn't bother me in the least,but who knows on this..Neat thread.

[BleedRed]

Anything that says Northstar........run, very fast!

[Gearheadtom]

My parents had a '99 Deville, nothing but trouble, nice car when it worked tho. Luckily they got rid of it before the head gaskets went, but the trans went when they had it (supposedly common), and I do remember something about an evap leak that took many trips to the garage to fix. Plus the garages charged more, just because it was a caddy.