Compression test inconclusive, though cyl leaking coolant
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Cadillac DeVille 1985 to 2005 including:
1985-1992 Fleetwood, 1993 Sixty Special, All FWD Forum Discussion, Compression test inconclusive, though cyl leaking coolant in Past Cadillac Vehicle Discussion; Ok. I think I have a head gasket leak. I have the dreaded Northstar on a 99 Deville 180x miles ...
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    xsmash is offline Cadillac Owners Member
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    Cool Compression test inconclusive, though cyl leaking coolant

    Ok. I think I have a head gasket leak. I have the dreaded Northstar on a 99 Deville 180x miles

    It started blowing white smoke out of its exhaust a week back. Here are the things that I have done to arrive at my conclusion.

    1. Compression test per repair manual - All cylinders are between 120 and 140 psi on 7 cranks. The cyl 6 was blowing coolant out, visibly when I was testing with the spark plugs out. This is how I know at least cyl 6 is bad.But it holds 140psi in compression.
    2. Reservoir is blowing bubbles -After I start the engine and leave it for about 10 mts, I see smoke coming out of the reservoir as distinct bubbles, every 4-5 seconds.
    3. Vehicle shudders during idle, sometimes during start from stop on a stop light. It also shudders while starting and then settles down to a nice idle.

    My question is if cyl 6 is bad, and blowing coolant, why is the compression still normal?
    Also if there are other cylinders that are bad, how will I know, since all cylinders hold the same compression? What test is conclusive and fool proof. I have a feeling I have more than 1 bad cyl, and the other might be in the back bay but I cannot tell. All the ceramics on the spark plugs on the back are charring brown - maybe its the O2 sensor, making it running lean? A combination of the above?

    Any help would be appreciated!

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    MoistCabbage's Avatar
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    Compression tests can be misleading when diagnosing HG issues, as you' e found out. A block test is the definitive test. It indicates if there are traces if exhaust gasses in the cooling system.

    That said, I think it's pretty clear you have HG issues. Also, it doesn't matter if more than one cylinder has failed, it's time to insert/stud the block, or get rid of the car.

    Do you know what's involved in Northstar HG repair?

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    Re: Compression test inconclusive, though cyl leaking coolant

    A compression test will not tell you if you have a blown HG. A leak down test will, but a block test is easier. An even easier test is to go back and smell the white "smoke" from the exhaust. If it is a HG it will smell sweet like coolant.

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    MoistCabbage's Avatar
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    But coolant spraying from the plug hole pretty much sums it up.

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    Re: Compression test inconclusive, though cyl leaking coolant

    you could do a BLOCK TEST -

    but - like MC said - "coolant spraying from the plug hole pretty much sums it up."

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    xsmash is offline Cadillac Owners Member
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    Re: Compression test inconclusive, though cyl leaking coolant

    Thanks for the input guys, I appreciate it!!
    So, if I see bubbles in the reservoir already, how would the block test be useful? Just saying, where else is the air coming from apart from the an exhaust leak into the cooling system?
    Is the engine shudder indicative of anything? If the hg is fixed would it go away? Cos it's been there for 2 years now - the entire period that I have owned the car.Which is close to 12k miles!!
    Is there a way to find out what cylinder the leak is located before moving on to fixing it, one way or the other. A test for it, maybe?

    @MoistCabbage - I have an idea, and I know it takes a lot. Or I'm just scared of it. The reason why I ask is cyl 6 is in front. I can tear it apart and fix it, and if there is a problem on the back bay, I'm still stuck. Or am I just completely seeing this wrong?

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    MoistCabbage's Avatar
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    As posted, there's really no point in doing a vlock test, you have coolant in cylinder 6.

    There is no test to tell which cylinder/s are affected, other than obvious signs of coolant in the cylinder, but it's very possible there are leaks in other cylinders that aren't large enough to be seen yet.. You'll know which ones were affected if and when you replace the gaskets and insert/stud the block.

    If you're trying to find out which cylinders are affected because you're hoping only one bank is in need of repair, don't other. Fixing one side is a waste of time and/or money due to the labor involved. Also, block sealer products WILL NOT WORK. They will, however, clog small coolant passages, and make a mess inside the engine that may or may not be able to be cleaned.

    Edit: You edited your post while I was typing.

    I figured you were hoping to fix just one bank if possible. While it is possible to insert/stud the front bank with the engine in place, because of the drilling and tapping involved, it is NOT recommended.

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    Re: Compression test inconclusive, though cyl leaking coolant

    how would the block test be useful?
    the BLOCK TEST is the definitive test for failed head gaskets in the Northstar motor -
    it will simply verify the presents of exhaust gasses in the cooling system -

    Is the engine shudder indicative of anything
    YES - a misfire -
    but a misfire could be caused by several things -
    no spark -
    no fuel -
    no compression -

    If the hg is fixed would it go away
    the best answer is POSSIBLY -

    Is there a way to find out what cylinder the leak is located
    before moving on to fixing it

    not really - but it doesn't matter anyhow -

    you don't "fix" just one cylinder - and for that matter -
    you don't just replace one head gasket -

    this is a ALL OR NOTHING repair -
    remove the engine -
    remove both heads -
    drill out and repair all 20 head bolt holes -
    put everything back together -
    put the engine back in -

    this isn't a "weekend" type job -

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    Re: Compression test inconclusive, though cyl leaking coolant

    Quote Originally Posted by xsmash View Post
    Is there a way to find out what cylinder the leak is located before moving on to fixing it, one way or the other. A test for it, maybe?
    Usually the spark plug in the offending cylinder will be very clean.

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    Re: Compression test inconclusive, though cyl leaking coolant

    .......... and again: To repair a Northstar with a failed head gasket on one cylinder bank You remove the entire engine from the car and repair BOTH banks at the same time.

    Depending on who does the job, you will get BigSerts, NS300 (Huhn) inserts, or studs used to repair all 20 cylinder head bolt holes - and the original GM head bolts are discarded - new bolts only - in inserts.

    (BigSert is the newer, beefier model of TimeSert from the Time Fastener Company)

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    xsmash is offline Cadillac Owners Member
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    Re: Compression test inconclusive, though cyl leaking coolant

    Sorry for the late update.
    So, I did the unthinkable...I did put in the nanotechnology magic potion in there, twice..for 2 cylinders..and voila..no smoke and running good so far. It was quite a task, but nothing close to removing heads on both banks!

    And, after all this - the check engine light is on and throwing two codes
    P0304 - Engine Cylinder 4 misfire
    P0174 - System Bank 2 lean...or something.

    Pulling my hair again, lost a lot of it so far...but car is running, but jerky, especially at the start.

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    Re: Compression test inconclusive, though cyl leaking coolant

    So, I did the unthinkable...
    I did put in the nanotechnology magic potion in there, twice..
    for 2 cylinders..and voila..no smoke and running good so far.
    It was quite a task, but nothing close to removing heads on both banks!

    that "band-aid" - at best - won't last long -
    I wouldn't spend another dime on "fixing" anything else -
    it is just wasting money on a junk engine -

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    What will u do when it fails?

    Eventually it will give out and ur back to where u started

    I've tied the magic potions and I can tell u that, at best, it's a temporary solution to a very big permanent problem

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    Re: Compression test inconclusive, though cyl leaking coolant

    The jerky starts is a dead giveaway - more gasket leaks, but now the problem is how to clean the stuff out of the entire cooling system during an engine top overhaul.

    A lean bank code usually points to a vacuum leak or intake air leak after the MAF.

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    Re: Compression test inconclusive, though cyl leaking coolant

    I cleaned it thoroughly!! I mean I ran about 30 gallons of water to rid of the stuff. The coolant that I put in after does not have residue in there.

    Submariner, thanks for the input.I was erring towards the vacuum leak, but where do I look? I am thinking of a smoke test.
    I have tried starting fluid through the intake and there is no revving up of the engine when I do it.
    Any thoughts.

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