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Mystery Coolant Leak 4.0 SOHC - Any Ideas?

Discussion in 'Stock 2002 - 2005 Explorers' started by jstaif, July 29, 2019.

^^Searches ExplorerForum.com^^





  1. jstaif

    jstaif New Member

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    Greetings, Looking for help on where my coolant is going to...

    Have an 02 Explorer with the 4.0 SOHC engine, high miles (286K). Coolant has been disappearing from the system at about 16+ ounces a week but can't find where it is going, have checked the following:

    Pressure tested the system, It holds pressure for the 30 minutes + that I have tested it for with no coolant appearing anywhere or any puddles on the ground. Not leaking through any external areas: No hose leaks, not leaking through the thermostat housing (new) or coolant temp sensor. No evidence of pooling on top of engine or anywhere else.
    Added the leak trace to the coolant but still found no leaks with black light anywhere under the hood after driving or while pressure testing

    Oil looks normal (no milkiness present).

    Ran the block tester CO test for at least 30 minutes and fluid stayed blue...no exhaust gases apparent in the coolant.

    Bought a new reservoir cap that holds the 16psi.

    Nothing noticeable is coming out of the exhaust i.e. smoke etc. Once in a while I smell coolant around the engine but usually not. Coolant might be disappearing at a faster rate when I drive at higher speeds 70mph +.

    No other symptoms exist, runs at normal operating temperature. I bought this car new and it has never been allowed to overheat.

    Wondering what internal interfaces exist for coolant leaks on this engine. It seems the the plastic intake manifold and exhaust manifold only mate to the head, so no water jacket interfaces are part of these interfaces.

    This would leave the Head Gasket coolant interfaces that I have not seen issues with:
    1) to the combustion chambers
    2) to the outside
    3) to the crankcase

    I'm feeling kind of stumped here. Am considering using Blue Devil in the coolant. Would like to get a few more years from this old gal.

    Any clues on where the coolant is going???
     
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  3. jstaif

    jstaif New Member

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    Forgot to mention, the plugs all looked normal and the same as each other.
     
  4. 974X4BLACKSPORT

    974X4BLACKSPORT Active Member

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    There is a vacuum operated servo that diverts hot water away from the heater core when the temp. select knob is on full "cold", this servo can leak small amounts of coolant out of the servo shaft seal when you are not looking. I think its called "temperature divert valve". Follow your heater hoses from the engine block all the way to the fire wall, it will be located on one of those heater hoses.
     
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  5. jstaif

    jstaif New Member

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    Went out and looked at this valve, it’s dirty but dry. Will monitor it. Thx.
     
  6. Tshaw88

    Tshaw88 New Member

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    Look on top of the block between the fuel rails behind the thermostat housing. Bottom gasket of therm housing is known to leak and coolant goes down onto the block, usually puddles in a freeze plug.
     
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  7. jstaif

    jstaif New Member

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    I had this issue with my wifes car, so I've been keeping an eye out for that. This car came with an NVH foam "pillow" which I took out so I could see the top of the block. Thanks for responding.
     
  8. sfhess

    sfhess Member

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    I just replaced all the hoses, o-rings and seals having to do with the thermostat housing. Had to improvise a bit on the hoses and one seal was particularly hard to find. Eliminated my leakage into the valley under the intake plenum.
     
  9. TechGuru

    TechGuru Well-Known Member

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  10. Tshaw88

    Tshaw88 New Member

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    My 05 didn't have the foam pillow, the motor I just put in was from an 02 and did have it, I left it in its supposed to help dissipate the heat I guess and where the intake it plastic I figured I'd leave it. I've run blue devil coolant stop leak through mine in the past, even if it doesn't seal the leak it does a good job of showing where it's leaking, I always pull the thermostat and clean up the thermostat and inside the housing afterwards though and put in fresh coolant just to be sure the stuff doesn't gunk up the thermostat on me.
     
  11. sfhess

    sfhess Member

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    "Blue Devil" is costly and worthless.
     
  12. Tshaw88

    Tshaw88 New Member

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    Depends how u use it, I add it at the thermostat let it run, spot the leak then dump the coolant, clean the thermostat and put it fresh coolant, I've only needed it twice to find leaks. It's not something is let stay in the heating system I learned that lesson the hard way.
     
  13. TechGuru

    TechGuru Well-Known Member

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    The only stop leak I'd use is this:

    [​IMG]
    I've used it without any problems. It's best for these hard to find tiny leaks.
     
    Last edited: August 17, 2019
  14. Gilligan

    Gilligan New Member

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    I've had a siiliar issue and found I needed to replace my pinch clamp hose clamps with full metal screw tight belt clamps. Fluid was leaking around the hose fittings but with the engine heat the evidence evaporated away.
     
  15. sfhess

    sfhess Member

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    I had my upper radiator hose, "secured" by the original spring clamp, blow off the radiator bung. I replaced the original spring clamps with worm screw clamps.
     
  16. Drewmcg

    Drewmcg Elite Explorer

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    Tech Guru: What product were you trying to show? Tx.
     
  17. TechGuru

    TechGuru Well-Known Member

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  18. blue xlt

    blue xlt New Member

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    Starting with engine cold,start engine and let it fast idle for 90 seconds. Shut off engine and get under truck at rear of engine and look up with strong flashlight. Your looking for coolant dripping down or greenish/yellow stains.By running for 90 sec,you are pressuring coolant system but engine is not hot enough to burn off fluid and leave no trace. Good luck.
     
  19. Drewmcg

    Drewmcg Elite Explorer

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    thanks
     
  20. Derrick Stoelton

    Derrick Stoelton New Member

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    Have you checked your oil cooler gasket?
     
  21. donalds

    donalds Elite Explorer

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    Use k-seal will stop the leak I think @koda2000 told me about it works wonders
     

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