Neglected 2001 DeVille/Overheating
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  • 1 Post By Submariner409
Cadillac DeVille 1985 to 2005 including:
1985-1992 Fleetwood, 1993 Sixty Special, All FWD Forum Discussion, Neglected 2001 DeVille/Overheating in Past Cadillac Vehicle Discussion; Hi all, Apparently I'm not new here as I was already registered, but this is my first post in forever. ...
  1. #1
    imautoparts is offline Cadillac Owners Member
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    Neglected 2001 DeVille/Overheating

    Hi all,

    Apparently I'm not new here as I was already registered, but this is my first post in forever.

    A handicapped friend of mine has a rather neglected 2001 Deville (Northstar), 185K miles, and it has begun to overheat. He has only driven it in the city, but it overheats within 10 minutes of starting the car even at idle. I'm trying to help him out as I believe these old Cadillacs to be very reliable as basic transportation. The car does not appear to leak coolant, but it boils over every time he drives it.

    There is no scum or indication in the coolant of oil contamination, and the engine oil is coolant free (taste tested).

    The thermostat was just changed, and I monitored the temp as the car warmed up and I can tell the thermostat is functioning normally. The turbulence in the overflow tank when the engine is revved is perfectly normal, so I'm not thinking head gasket.

    The two electric fans remain off even while the radiator is boiling over. I'd like to wire them to be on all the time if the ignition is on, so I plan to bridge the relays.

    Am I on the right track here? Am I missing anything obvious?

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  3. #2
    basscatt's Avatar
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    Re: Neglected 2001 DeVille/Overheating

    Quote Originally Posted by imautoparts View Post
    Hi all,

    Apparently I'm not new here as I was already registered, but this is my first post in forever.

    A handicapped friend of mine has a rather neglected 2001 Deville (Northstar), 185K miles, and it has begun to overheat. He has only driven it in the city, but it overheats within 10 minutes of starting the car even at idle. I'm trying to help him out as I believe these old Cadillacs to be very reliable as basic transportation. The car does not appear to leak coolant, but it boils over every time he drives it.

    There is no scum or indication in the coolant of oil contamination, and the engine oil is coolant free (taste tested).

    The thermostat was just changed, and I monitored the temp as the car warmed up and I can tell the thermostat is functioning normally. The turbulence in the overflow tank when the engine is revved is perfectly normal, so I'm not thinking head gasket.

    The two electric fans remain off even while the radiator is boiling over. I'd like to wire them to be on all the time if the ignition is on, so I plan to bridge the relays.

    Am I on the right track here? Am I missing anything obvious?
    ----------------------------
    check the PURGE LINE -
    the PURGE LINE is the only way of expelling air from the Northstar cooling system -

    it is a 3/8 diameter hose that goes from a hollow bolt in the thermostat/waterpump housing area of the engine - and plugs onto a nipple on the side of the SERGE TANK -

    with the engine running - there should be a gentle - constant flow of coolant - from the engine - to the serge tank -

    if there is no flow - the most likely cause is a blockage in the hollow bolt -

    follow the hose towards the engine - with the engine OFF - remove the hose - use a straightened metal coat hanger - or something similar - and poke it into the hollow bolt -

    the coat hanger should go in about 2 1/2 inches -

    once the hollow bolt is cleared - you can briefly start the engine to verify coolant flow - be sure to use some sort of container to catch the coolant so you don't make a mess -

    check the hose and serge tank for blockage -

  4. #3
    ryannel2003's Avatar
    ryannel2003 is offline Cadillac Owners Connoisseur
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    Re: Neglected 2001 DeVille/Overheating

    The very FIRST thing I would do is head down to your local AutoZone, Advanced Auto, O'Reilly's, etc. and pick up a block tester. Follow the instructions and if the fluid changes color AT ALL... you're looking at a blown headgasket. Motor has to be dropped and all 20 head bolts have to be re-tapped and inserts installed. $5k fix at a dealership or $2k-$3k at an independent shop. If you do choose to get engine fixed, ONLY have a person repair it who is knowledgeable with the Northstar engine.

    Good luck but it's not sounding too good. These engines very, very rarely mix oil with coolant, smoke at startup (unless in advanced stages of HG failure) or ever act strange other than loosing coolant and overheating.

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    imautoparts is offline Cadillac Owners Member
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    Re: Neglected 2001 DeVille/Overheating

    Well, the block test is $8, so I think I'll do the purge line cleanse first, add fresh dex coolant and hotwire the fan switch to 'on'. If that doesn't do it the next logical step is of course the block test. Frankly considering the notorious issue with the heads loosening up I'm not as hopeful as I was. Who ever heard of a head gasket leak that doesn't pressurize the tank or cause scum? Well, live and learn.

    The cost of coolant is really the issue here, as we have cold winters. In the summer for his short trips he can replenish the water every morning.

  6. #5
    ryannel2003's Avatar
    ryannel2003 is offline Cadillac Owners Connoisseur
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    Re: Neglected 2001 DeVille/Overheating

    Quote Originally Posted by imautoparts View Post
    Well, the block test is $8, so I think I'll do the purge line cleanse first, add fresh dex coolant and hotwire the fan switch to 'on'. If that doesn't do it the next logical step is of course the block test. Frankly considering the notorious issue with the heads loosening up I'm not as hopeful as I was. Who ever heard of a head gasket leak that doesn't pressurize the tank or cause scum? Well, live and learn.

    The cost of coolant is really the issue here, as we have cold winters. In the summer for his short trips he can replenish the water every morning.
    Absolutely. I typically forget about the purge line being an issue but most of the time (not all) it is the headgasket that fails. The Northstar is a good, but sometimes problematic engine. On my 2000 STS the headgasket blew at 54k miles and it was leaking oil. My Deville doesn't leak or use a drop of oil. (I'm not going to say anything about HG as it would blow tomorrow LOL).

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    rodnok01's Avatar
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    Re: Neglected 2001 DeVille/Overheating

    I would start checking the fuses and relays for the fans, if the display is reading correct temp the fans should be coming on. The relays are know to corrode and cause issues.
    Do the fans come on with the AC on?

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    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: Neglected 2001 DeVille/Overheating

    Hot wiring the fans will accomplish exactly nothing - except cost you alternator load and fuel mileage. Troubleshoot the fan system - don't jury-rig it.
    zergkiller likes this.

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    Re: Neglected 2001 DeVille/Overheating


    The fans will not cause it to overheat like that anyway.

    Don't worry about "cleansing" the purge line. Just be sure it is clear and flows coolant.

  10. #9
    imautoparts is offline Cadillac Owners Member
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    Re: Neglected 2001 DeVille/Overheating

    Upon further reading of replies and thinking I'm going to do the block check first. Only once we know that can we determine if the car is worth even putting a gallon of fresh antifreeze in, let alone other repairs.

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    Ranger's Avatar
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    Re: Neglected 2001 DeVille/Overheating

    Checking the purge line is free. Do that first.

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    basscatt's Avatar
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    Re: Neglected 2001 DeVille/Overheating

    Quote Originally Posted by Ranger View Post
    Checking the purge line is free. Do that first.
    -----------------------------------
    and a blocked purge line is a lot more common than failed head gaskets -

  13. #12
    imautoparts is offline Cadillac Owners Member
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    Re: Neglected 2001 DeVille/Overheating

    Ok, here's where we are now.

    1. Changed thermostat
    2. Cleared purge line (it appeared to be ok)
    3. Performed block check for 10 minutes at the reservoir, NO COLOR CHANGE at all, the prettiest jar of blue fluid you ever saw. I compared it closely to some new fluid and the color hadn't changed a bit.
    4. Installed fresh Dex coolant in proper ratio
    5. Tested both cooling fan relays, both OK (tested them by replacing the engine ignition relay (it is the same) and both tested fine)
    6. I tried to jump across the relay pins to get the fans to run manually, I was unable to get them to run - but since I'm not familiar with the cadillac
    relay system I might have been doing it wrong. I did verify I have 12V at the #30 pin on both relays, but I tried both power and ground at the other
    and got nothing from the fans. I was using a length of copper wire with one end hammered down to match the relay pins. If as I'm suspecting the relay
    controls the ground side I probably didn't properly crosswire it to ground - maybe somebody can help me verify if the fans themselves work?

    When we test drove the car it overheated immediately, just like it did when we had 100% water in the car. Cap has been tested OK.

  14. #13
    rodnok01's Avatar
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    So you checked the hollow bolt? If not the system will not purge air and overheat quickly.
    If the actual bolt is clear I would suspect the rad of being blocked or a hose collapsing.

  15. #14
    Ranger's Avatar
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    Re: Neglected 2001 DeVille/Overheating

    Have you verified that coolant actually flows out of the purge line while at idle?

  16. #15
    basscatt's Avatar
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    Re: Neglected 2001 DeVille/Overheating

    Quote Originally Posted by imautoparts View Post
    Ok, here's where we are now.

    1. Changed thermostat
    2. Cleared purge line (it appeared to be ok)
    3. Performed block check for 10 minutes at the reservoir, NO COLOR CHANGE at all, the prettiest jar of blue fluid you ever saw. I compared it closely to some new fluid and the color hadn't changed a bit.
    4. Installed fresh Dex coolant in proper ratio
    5. Tested both cooling fan relays, both OK (tested them by replacing the engine ignition relay (it is the same) and both tested fine)
    6. I tried to jump across the relay pins to get the fans to run manually, I was unable to get them to run - but since I'm not familiar with the cadillac
    relay system I might have been doing it wrong. I did verify I have 12V at the #30 pin on both relays, but I tried both power and ground at the other
    and got nothing from the fans. I was using a length of copper wire with one end hammered down to match the relay pins. If as I'm suspecting the relay
    controls the ground side I probably didn't properly crosswire it to ground - maybe somebody can help me verify if the fans themselves work?

    When we test drove the car it overheated immediately, just like it did when we had 100% water in the car. Cap has been tested OK.
    ---------------------------
    When we test drove the car it overheated immediately
    about the ONLY thing that will cause that is -
    AIR IN THE COOLING SYSTEM -

    and the ONLY way to eliminate the air from the cooling system -
    is through the PURGE LINE -

    did you actually witness coolant FLOWING THROUGH the PURGE LINE at idle?

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