Is it a head gasket?
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Northstar Engines and System Technical Discussion Discussion, Is it a head gasket? in Cadillac Engine Technical Discussion; Hello boys and girls! I just obtained a '99 Seville STS for cheap because it is loosing coolant. I've read ...
  1. #1
    petr0157 is offline Cadillac Owners Member
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    Is it a head gasket?

    Hello boys and girls! I just obtained a '99 Seville STS for cheap because it is loosing coolant. I've read about the typical head gasket issues but I just cannot accept that is the case here. Here are the details:

    no overheating - car runs excellent
    no coolant being blown out the expansion tank
    no coolant in oil (the oil is not milky)
    there is white smoke coming out the tail pipe
    coolant level goes down slowly (I don't see any leaks)

    I took off the intake manifold and found coolant in it (maybe 2-3 oz) which would explain the white smoke. The question is where is it coming from. If it is the head gasket I don't know by which law of physics it would end up in the intake manifold (unless there is something specific to the Northstar that I don't know). I am suspecting anything that has coolant connection to the manifold - throttle body, EGR valve.

    Am I wasting my time by avoiding the real problem (the head gasket) here? If someone can explain clearly how a bad head gasket can push the coolant into the intake, I will be convinced. This is the first Cadillac I bought so I am just a newbie here. An impressive car though... Thanks!

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    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: Is it a head gasket?

    Head gaskets rarely leak internally and almost never put coolant in the oil on a Northstar, but using coolant and steamy exhaust are not good signs. Not sure how coolant would get into the TB though.

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    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: Is it a head gasket?

    Did 99 have the external coolant lines to and from the throttlebody casting ? 2000+ uses a passage cast into the water crossover manifold, but I think 99 had a different TB heater system.

  5. #4
    zonie77 is offline Cadillac Owners Connoisseur
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    Re: Is it a head gasket?

    Quote Originally Posted by petr0157 View Post
    Hello boys and girls! I just obtained a '99 Seville STS for cheap because it is loosing coolant. I've read about the typical head gasket issues but I just cannot accept that is the case here. Here are the details:
    If you read many of the HG threads they have the same theme...I cannot accept that's the case here.

    no overheating - car runs excellent
    no coolant being blown out the expansion tank
    no coolant in oil (the oil is not milky)
    there is white smoke coming out the tail pipe
    coolant level goes down slowly (I don't see any leaks)
    Nothing you said eliminates HG's, the last two indicate it.

    I took off the intake manifold and found coolant in it (maybe 2-3 oz) which would explain the white smoke. The question is where is it coming from. If it is the head gasket I don't know by which law of physics it would end up in the intake manifold (unless there is something specific to the Northstar that I don't know). I am suspecting anything that has coolant connection to the manifold - throttle body, EGR valve.
    Deceleration will pull some gases from the combustion chambers into the intake, if you have coolant in the combustion chambers...
    This is the same way oil gets on the throttle body.

    Am I wasting my time by avoiding the real problem (the head gasket) here? If someone can explain clearly how a bad head gasket can push the coolant into the intake, I will be convinced. This is the first Cadillac I bought so I am just a newbie here. An impressive car though... Thanks!
    There are several tests for HG leaks. An exhaust gas test is the easiest and probably cheapest. Make sure the car is driven before the test, just idling it may not give enough combustion pressure if the HG's still have some sealing pressure (which yours probably do).

  6. #5
    petr0157 is offline Cadillac Owners Member
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    Re: Is it a head gasket?

    What you guys are saying makes a lot of sense. Oil and HC do end up in the TB so with the water must be the same way.

    The TB has coolant hoses going through it (to answer submariner409).

    Now that the intake is off the engine I see that the crossover gasket is wet and I think I see traces of red coolant towards the intake manifold which is very close. I know that the intake gaskets did not seal very well because there is oil on the outside of the seals and the bolts were sort of loose. So now I am thinking that it might be as simple as an external leak being sucked right into the intake. I am almost tempted to replace the crossover gaskets (might as well do the water pump at the same time) and the intake manifold gaskets and see what happens. I hate to do unnecessary work but still my gut feeling is that the HG is good. Or maybe I should put everything together and do the exhaust test. We'll see...

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    Ranger's Avatar
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    Re: Is it a head gasket?

    That crossover manifold is supposed to be a real bitch of a job.

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    Re: Is it a head gasket?

    Quote Originally Posted by Ranger View Post
    That crossover manifold is supposed to be a real bitch of a job.
    Awful job, in the car.

    Bypass the throttle body coolant as a test, to see if the coolant is coming form there, but I doubt it.

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    jeffrsmith is offline Cadillac Owners Fanatic
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    Re: Is it a head gasket?

    Quote Originally Posted by tateos View Post
    Awful job, in the car.
    I didn't find it particularly easy even when the engine was out of the car, the wiring harness makes it a total PITA.

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    zonie77 is offline Cadillac Owners Connoisseur
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    Re: Is it a head gasket?

    Quote Originally Posted by petr0157 View Post
    What you guys are saying makes a lot of sense. Oil and HC do end up in the TB so with the water must be the same way.


    Now that the intake is off the engine I see that the crossover gasket is wet and I think I see traces of red coolant towards the intake manifold which is very close. I know that the intake gaskets did not seal very well because there is oil on the outside of the seals and the bolts were sort of loose. So now I am thinking that it might be as simple as an external leak being sucked right into the intake. I am almost tempted to replace the crossover gaskets (might as well do the water pump at the same time) and the intake manifold gaskets and see what happens. I hate to do unnecessary work but still my gut feeling is that the HG is good. Or maybe I should put everything together and do the exhaust test. We'll see...

    If you had an intake leak bad enough to pull coolant into the intake it would not be running very well. It took me a long time to accept HG's the first time but that is the likely problem.

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    Re: Is it a head gasket?

    Quote Originally Posted by jeffrsmith View Post
    I didn't find it particularly easy even when the engine was out of the car, the wiring harness makes it a total PITA.
    Yes - I agree with you - in fact, I was going to say that, but I thought maybe my recollection was worse than it really was. Some of those bolts really are hard to get at.

  12. #11
    petr0157 is offline Cadillac Owners Member
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    Re: Is it a head gasket?

    A little update: I cleaned the intake manifold (as much as I could) and put it back. I decided not to replace the intake gaskets and also I used silicon sealer in addition just in case. I bypassed the TB heater line, removed the EGR line and even the PCV lines. So basically the only thing connected to the intake manifold is the fuel pressure vacuum line. Everything else is pluged. Now the results:

    Initially the car smoked just as bad but it was cold so all cars were smoking. Now it is quite warm (35F) and yesterday there was very little smoking. I think it smells more like exhaust/oil burn rather than a sweet antifreeze smell. Since this is my first Cadillac I just don't know how much smoke is normal (it is a big engine and known to burn oil). First I noticed coolant just under the EGR valve (below the crossover). Then the next time I drove the car the spot evaporated and is now dry. Sometimes it seems to use more coolant than other times.

    One additional piece of information: it always misfires when first started. Then couple of minutes later it runs smooth. Still no overheating issues even if I floor it a few times.

    Any thoughts will be appreciated!

  13. #12
    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: Is it a head gasket?

    Replace the EGR and any vacuum lines, including the PCV system. Your engine will never run correctly without them all, and the plugged PCV leads to crankcase overpressure which will wind up blowing oil out of ANY available weak gasket. The fuel mixture and vacuum will never be correct with a removed EGR.

    Sounds more like you have a bad injector or fuel pressure regulator. Both diagnoses are posted in this forum as well as up in Seville/Deville.

    DO NOT fill the coolant reservoir more than halfway, COLD. Check your pressure cap. It should hold 16 psi (2000 went to 18 psi.).

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    Ranger's Avatar
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    Re: Is it a head gasket?

    One additional piece of information: it always misfires when first started. Then couple of minutes later it runs smooth.
    That's a HG symptom. Buy or rent the block test kit and rule out or condemn the HG's. Then go from there.

  15. #14
    petr0157 is offline Cadillac Owners Member
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    Re: Is it a head gasket?

    OK, thanks to everyone that contributed. I knew about testing for exhaust gases in the coolant but thought that repair shops do it with expensive emission testers. As soon as I read Ranger's comment I went and bought the test kit for $40 from NAPA. It's confirmed, it's the headgasket. Turned yellow at 5-6 squeezes. Now I will check which bank it is just to know but I'll probably just replace the whole engine with a used one from the local junkyard for $750. Since I don't have any money right now, I'll probably start ripping it apart but if I need to put in the time-serts it will be costly (the cheapest I found them was $400). Anyways, thanks again!

  16. #15
    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: Is it a head gasket?

    You need to look at Norm's Inserts and www.northstarperformance.com (cylinder block head studs) before you start a top overhaul.

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