Please help diagnose my cooling system problem
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Northstar Engines and System Technical Discussion Discussion, Please help diagnose my cooling system problem in Cadillac Engine Technical Discussion; Specs: 2000 deville History: Engine has always smelled 'burnt' since I purchased the vehicle 5 years ago. Engine has always ...
  1. #1
    d1mbu1b is offline Cadillac Owners Member
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    Please help diagnose my cooling system problem

    Specs:
    2000 deville

    History:
    Engine has always smelled 'burnt' since I purchased the vehicle 5 years ago.
    Engine has always required periodic refill of coolant.
    Overflow tank plastic nipple broke off lower rear... I replaced last year (including fill cap)
    Plastic radiator end-caps burst... I replaced 6 mo. ago.
    I have probably consistently overfilled reservoir to "full cold" "do not over fill" ... this must have lost meaning when translating form Chinese to English
    I have periodically added the "coolant tabs" every year.

    Symptoms:
    The motor overheated (slightly) today for the first time.
    The car was shut down right when it began to overheat
    The radiator fans are on.
    The reservoir is full up to the top.
    after running a bit more, the motor cooled back down and the coolant reservoir emptied back into the block leaving about an inch of coolant in the reservoir.
    At this point there is still significant pressure in the reservoir even though it is mostly empty.

    Guess:
    My theory is that the reservoir continually weeps out the overflow/fill cap causing a lack of coolant in the block.
    The lack of coolant in the block causes the thermostat not to be in contact with the coolant.
    The thermostat stays shut until the overheated block heats it up to open instead of hot coolant.
    Once the thermostat opened the excess coolant in the reservoir and radiator was able to be sucked back in and cool the block.
    This is just a guess since I don't know how the cooling system is plumbed.

    Please Help:
    Please let me know if anyone has experienced similar problems.
    Any hints are appreciated.


    Thank you.

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    tateos's Avatar
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    Re: Please help diagnose my cooling system problem

    Head gasket

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    CadillacLuke24's Avatar
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    Re: Please help diagnose my cooling system problem

    For starters, pull your codes, and post their definitions with the codes here. Sticky in the DeVille/FWD forum on how to do that. Second, stay far away from those pellets. GM doesn't use them anymore, and the best you could accomplish with them is a clogged heater core.

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    Ranger's Avatar
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    Re: Please help diagnose my cooling system problem

    My theory is that the reservoir continually weeps out the overflow/fill cap causing a lack of coolant in the block.
    The only way that will happen is if the cap is not holding pressure causing the coolant to boil, but you already replaced the cap. Borrow a block test kit from AutoZone (just pay for the test fluid) and test the surge tank after an overheat episode for the presence of exhaust gases. I tend to agree with Tateos.

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    Submariner409's Avatar
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    Re: Please help diagnose my cooling system problem

    d1mbu1b, "Translating from Chinese" .......... Where are you ???

    The Northstar cooling system is different from the usual front-of-the-block water pump and crossovers. This engine uses a water crossover at the rear (driver's end) of the block - attached to ports on the two cylinder block banks and the cylinder heads. The heater circuit is the primary coolant circulation piping - the coolant reservoir 'rides' on the heater coolant return line to the water pump in the crossover. As the engine and heater circuit reaches 188 degreesF the thermostat (in the radiator return hose) begins to open, allowing coolant to begin circulating from the water pump, through the radiator, past the partially open thermostat and back to the system. As the entire system now heats further, the thermostat will become fully open at 206 degrees. Most Northstars run at about 190 - 198 degreesF on the open road, so the thermostat is only about 75% open under road conditions.

    The fans may run in either SLOW (series voltage supply) or FAST (parallel voltage supply). Fans run in SLOW at 224 degreesF and FAST at 236 degreesF. If an A/C function is selected, fans run in SLOW all the time, so the temperature gauge needle should sit at 12:00 o'clock. If the needle moves to about the first tick mark past 12:00, fans start. With no A/C function selected, in traffic or very slow driving the gauge needle will slowly move toward the first tick past 12:00, fans come on, the system cools to 213 degreesF, fans stop - and the cycle then repeats.

    Ranger, Where's that page of snakes that is the Northstar cooling system flow diagram ?

  7. #6
    d1mbu1b is offline Cadillac Owners Member
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    Re: Please help diagnose my cooling system problem

    Quote Originally Posted by tateos View Post
    Head gasket
    Thank you,
    Should I see water in the oil?

    ----------

    Quote Originally Posted by CadillacLuke24 View Post
    For starters, pull your codes,.
    Thank you,
    P0174 Fuel trim system lean bank 2. Is this due to being overheated???\
    P1860 torque converter clutch pulse width modulation solenoid - I have had this code from the start, we dont drive at highway speeds.

    ----------

    Quote Originally Posted by Ranger View Post
    Borrow a block test kit from AutoZone (just pay for the test fluid) and test the surge tank after an overheat episode for the presence of exhaust gases. I tend to agree with Tateos.
    Thank you,
    Will do.

    ----------

    Quote Originally Posted by submariner409 View Post
    d1mbu1b, "Translating from Chinese" .......... Where are you ???
    Thanks for all the info.
    I am in FLA.
    I can never figure out what "full cold don't overfill" means. + made in China = ???

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    Re: Please help diagnose my cooling system problem

    No coolant in the oil in a Northstar with failing head gaskets.

    P0174 - No, that's a vacuum leak. Hose, gasket ? Use a mechanic's stethoscope to snoop for hissssses.
    P1860 - The TCC will engage/disengage at about 43 mph ^ / v under light to moderate road loads. You don't have to be on the highway.

    The molded arrow on the reservor goes to the "FULL COLD" line. "DO NOT OVERFILL" means just that: An overfilled Northstar coolant reservoir will blow coolant all over the place as the coolant expands from normal heating - coolant expansion is the physical reason that today's systems automatically pressurize themselves to 16 or 18 psi in order to prevent water pump cavitation and to raise the boiling point of the coolant mixture.

    Update your profile with the car, year, model, miles. The info makes diagnosis a lot easier.

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    Re: Please help diagnose my cooling system problem

    ^^^ These guys hit the nail on the head. They're the best Find out if your HGs are bad, and then we can worry about the little stuff.

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    Re: Please help diagnose my cooling system problem

    This is just a guess since I don't know how the cooling system is plumbed.
    Ranger, Where's that page of snakes that is the Northstar cooling system flow diagram ?
    Here ya go.
    Attached Images

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    Re: Please help diagnose my cooling system problem

    Exploding side tanks? Coolant being pushed from low level up to top of reservoir? Constant refilling? Overheating?

    That's about as close to a confirmed HG problem as you can get w/o a block test.

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    Re: Please help diagnose my cooling system problem

    Quote Originally Posted by drewsdeville View Post
    Exploding side tanks? Coolant being pushed from low level up to top of reservoir? Constant refilling? Overheating?

    That's about as close to a confirmed HG problem as you can get w/o a block test.
    LOL - that's what I'm saying!

  13. #12
    d1mbu1b is offline Cadillac Owners Member
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    N* HG 12 step program

    Now that I have been through the "N* HG" "12 step" program...(denial, anger, ...)
    I have another Q:
    Will the computer tell my AC to blow hot after the motor overheats?

    The AC stopped coincidentally the same exact time as the over heat episode.

    I ask since, I can not sell the car like this, and I'm not sure I want to invest in fixing it.
    So, I have just been limping along until I replace it.

    Would be nice to have AC in the meantime.

    Thanks again for all the insight and help.

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    Re: Please help diagnose my cooling system problem

    Yes, when the engine overheats you should see a message saying something like ENGINE HOT IDLE ENGINE A/C OFF, but I think it should be enabled again once it cools off.

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    Re: Please help diagnose my cooling system problem

    Quote Originally Posted by Ranger View Post
    Yes, when the engine overheats you should see a message saying something like ENGINE HOT IDLE ENGINE A/C OFF, but I think it should be enabled again once it cools off.
    Yup - Ranger is correct - if you're AC still doesn't work, then something else is amiss. Maybe you disturbed something while doing repairs or diagnosis of the HG problem... like maybe something that caused a refrigerant leak - that will keep the AC from coming on, but should also be displaying a code

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    d1mbu1b is offline Cadillac Owners Member
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    Re: Please help diagnose my cooling system problem

    Thanks again. I wish I did honk something up; but all I did was add coolant.

    The car is running fine.
    The AC blows hot air, it seems to be hotter than the air when the AC of off, that could be my imagination.

    Is there a procedure to reset things, like disconnecting the battery or something?

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