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Thermostat housing leak

Discussion in 'Stock 2002 - 2005 Explorers' started by Austin Rueschhoff, August 20, 2019.

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  1. Austin Rueschhoff

    Austin Rueschhoff New Member

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    A few months back I had my thermostat housing crack badly and spew coolant everywhere. I was afraid of a blown head gasket at the time but the mechanic said it was alright and replaced the thermostat housing. The new housing was leaking and I had to refill coolant fairly often. Eventually the thermostat was giving bad reads (temp gauge would float up and down) so the mechanic put a new thermostat housing in.

    Coolant leaks were still happening and about a month later I started getting bad temp reads again. Coolant still leaking from housing and pooling up in "valley" behind thermostat housing. Mechanic again replaced housing.

    So, now I am on my third thermostat housing in a couple month and this one is leaking badly too - from all the seams and seemingly anywhere it could leak.

    Either one of two things is happening....I somehow keep getting crap parts, or, there is simply too much pressure in the cooling system for the thermostat housing to contain the coolant. Any thoughts??

    This is an 03 Ford Explorer 4.0L
     
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  3. BrooklynBay

    BrooklynBay Moderator & long time member. Staff Member Moderator Elite Explorer

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  4. Austin Rueschhoff

    Austin Rueschhoff New Member

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  5. BrooklynBay

    BrooklynBay Moderator & long time member. Staff Member Moderator Elite Explorer

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  6. Drewmcg

    Drewmcg Elite Explorer

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    What brand housings have been used for replacement?

    Never heard of excess coolant system pressure (but for overheating). Constricted radiator might conceivable cause this? Try coolant system flush with the Motorcraft chemical.
     
  7. 03Explo20

    03Explo20 Active Member

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    Keep in mind that you get what you pay for! You buy a cheap no name brand and this is what happens! Replace it with a quality name brand replacement and you'll be okay (Motorcraft, Gates).
     
  8. neilpridenz

    neilpridenz New Member

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    Hi,

    I had this exact problem a couple of years ago. I'm still asking myself why Ford make cooling components out of plastic! I couldn't find a metal alternative anywhere...

    Replaced the thermostat housing and on advice from others bought a genuine Motocraft replacement. There were some things I believe were important to a successful repair - the top of the head where the housing fits was a bit corroded and I was concerned about a poor seal being achieved, so I cleaned it thoroughly and buffed with some very fine emery paper on a flat piece of wood to avoid uneven spots. I used a new seal, and smeared a trace of medium-duty RTV silicone (the grey type) over each mating part before assembly.

    I did this very carefully but was a bit dismayed a few days later to see coolant still leaking and pooling in the valley between the heads. This turned out to be coming from the temperature sensor on the top of the housing - the o-ring had worn down over the years and I had not replaced it - new o-ring cured it completely.

    All good for a couple of years and a leak returned. This time it turned out to be the large-o-ring at the top of the housing, which I had replaced but balked at the local Ford New Zealand price for what is a simple o-ring - about NZ$30, US$20... I took the old one to an enginering supplies shop and got one for 20c instead. That worked out OK but it must have been a marginally smaller size, metric instead of imperial, or different material or similar as it flattened out and got hard, then started to leak a little. Fortunately I had bought one from RockAuto for US$0.50 with some other order as a just-in-case and that quickly cured the new leak.

    My 2c worth is that the design is not great - the seal between the housing and the head looks very fragile at best and needs assembled carefully to avoid nipping the square sealing ring. I bought a spare one just in case.

    If I did it again I would replace all o-rings and seals with new Motocraft ones (my 'close enough' one was a waste of time). The tolerances are quite close and think it is worth the extra to spend on OEM parts.

    Neil
     
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  9. Austin Rueschhoff

    Austin Rueschhoff New Member

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    Thanks all. I am not sure what brand the replacement housing is as I had a shop do it. Sounds like I need to try a better brand or better shop. Sounds like something easy to do myself with a motorcraft housing.
     
  10. neilpridenz

    neilpridenz New Member

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    Yup, I found the job reasonably easy to do myself, if you are comfortable with working on the engine, draining the coolant etc yourself you should be fine.

    There are some awkward hose clips to get in place as they all get cramped for space around the housing, I remember the short bypass hose was tricky. Good luck!
     
  11. Drewmcg

    Drewmcg Elite Explorer

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    A couple of notes in addition to prepping the block surface as mentioned:
    • the housing has two parts, an upper and a lower. Either/both can fail (separately). Unless you're sure, replace both;
    • the lower housing has a rather strange, flat, round gasket (sold separately by Ford) that kinda sits on its side in a groove in the lower housing. Replace it;
    • The upper housing is sealed against the lower housing using the rubber gasket built into the thermostat. Be sure that rubber surface points UP when you place the (new, Motorcraft) t-stat into the lower housing;
    • Be sure to carefully torque all six housing bolts. Consider replacing rusty ones or those with damaged heads. I like to use never-seize on the threads;
    • Replace the sensor(s), or at least the rubber o-ring (if you can find it) for the sensor.
     
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  12. miker104

    miker104 Active Member

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    In addition to the above, consider replacing the bypass hose that connects the housing to the water pump at the same time.

    Motocraft PN F77Z8548AF
     
  13. Austin Rueschhoff

    Austin Rueschhoff New Member

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    Hey all, thanks for your help so far. The shop has confirmed that I am getting combustion gasses in the coolant system, leading to increased pressure and failure of the thermostat housing. At this point I think the Explorer is pretty much toast as it isn't worth it to do any work on the head gaskets. I was thinking about trying some Bar's Leaks head gasket repair as a last ditch effort, but it would probably require replacing the thermostat housing again if it worked.

    Any thoughts on this? Probably a waste of effort but I thought it might be worth a shot.

    I don't have a lot of experience buying car parts. Can anyone link to a good source for a motorcraft thermostat housing? I appreciate it!
     
  14. Drewmcg

    Drewmcg Elite Explorer

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    Why not replace the head gaskets?
     
  15. Austin Rueschhoff

    Austin Rueschhoff New Member

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    Well its an '03 with 200k miles and has some other minor issues. I think the cost of replacing the head gaskets would be close to the value of the car.
     
  16. BrooklynBay

    BrooklynBay Moderator & long time member. Staff Member Moderator Elite Explorer

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  17. Drewmcg

    Drewmcg Elite Explorer

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    Then sell it with notice that it needs head gaskets. Some DIYer will buy and do the job him/herself. It's not that hard, though you need a good torque wrench and good sockets.

    No way I'd put money into a truck that needs new head gaskets without fixing them! Your three failed thermostats are perfect illustration
    If not thermostat housing, them you will bust radiator, or heater core, or hoses,, etc.
     
  18. BrooklynBay

    BrooklynBay Moderator & long time member. Staff Member Moderator Elite Explorer

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  19. Austin Rueschhoff

    Austin Rueschhoff New Member

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    I don't believe this one has a radiator cap. Unless you mean the coolant reservoir cap.
     
  20. BrooklynBay

    BrooklynBay Moderator & long time member. Staff Member Moderator Elite Explorer

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  21. BrooklynBay

    BrooklynBay Moderator & long time member. Staff Member Moderator Elite Explorer

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