How To Install A Thermostat

Discussion in 'Fox 5.0 Mustang Tech' started by xplhavoc, Dec 4, 2003.


  1. xplhavoc

    xplhavoc New Member

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    I have done it 4 times and it still leaks from the bottom. Can someone tell be the exact way to place the silicone and gasket? It goes silicone on motor part then gasket then thermo then silicone then the howsing right???
    thx
    #1
  2. flyinghi3

    flyinghi3 Member

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    make sure the thermostat is siting in the grove of the water nech housing. if not that one way it can cause a leak. By the way what type of water neck do you have? if you have one thats chrome they are crap. they end up warping from the heat.
    #2
  3. Michael Yount

    Michael Yount Advanced Member

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    Two things will help a lot. One is to use the gasket that has adhesive on one side. It will hold the t'stat in the housing groove as described in the previous post. The other thing that I've found helps immensely is to be sure you're not trying to put it back in with either the upper hose or the bypass hose attached. Take them both loose from the housing, and remove the bypass hose completely. It always interferes causing misalignment of things. Once you've got the housing bolted on, then attach all your hoses. Be sure you put the spring side towards the engine.
    #3
  4. somersdp

    somersdp New Member

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    Are you just replacing it and cranking it up to test for leaks. You need to let the RTV set up for a good couple hours. then crank it and chack it.
    #4
  5. Starscream88

    Starscream88 New Member

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    Take the Thermostat housing off completley

    CLEAN the hell out the back of it where it touches the intake on a bench grinder (with a wire wheel)

    Clean the intake where the thermostat housing meets each other,
    Get an ORIGINAL MOTORCRAFT thermostat, They twist into the thermostat housing ans LOCK into place,
    No need to worry about it falling out,

    You dont even need rtv,
    Then match the gasket, place the 2 bolts in, and torque up,
    I do these at work all the time and never use silicone,
    If you clean it all up you dont even need to use it,
    #5
  6. YardSpecial

    YardSpecial New Member

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    NEVER use RTV !!!

    Why do people use it??

    Permatex High tack is the stuff to use.

    From the guy who knows.
    #6
  7. RydeOn

    RydeOn Licensed to Chill Founding Member

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    I dunno, why do people use gaskets? When I use gaskets they always leak. So for the last 6 years I use RTV and no gaskets, works every time.
    #7
  8. Michael Yount

    Michael Yount Advanced Member

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    With the proper gasket and clean surfaces, no rtv is required; and no time waiting for rtv to set up. Bolt it up and go.
    #8
  9. YardSpecial

    YardSpecial New Member

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    U have to know HOW to use RTV properly.

    RTV is VERY dangerous stuff if it gets loose in the oiling, coolant system.

    U learn that the first day of school.

    I only use RTV (very small) in corners of intake and oil pans, thats it !!

    Use permatex high tack for the rest.


    I have a 25 year old engine with seeps, but no LEAKS !!!
    #9
  10. xplhavoc

    xplhavoc New Member

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    Yeah i bet the thermostat fell out of the grove i bet that is it. Ill use no rv and make sure its in place. I have the wire wheel so ill get it clean again and let you guys know thx..
    jeff
    #10
  11. Michael Yount

    Michael Yount Advanced Member

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    Cavallo is right - with paper gaskets, all that's needed is a the proper gasket dressing (not rtv); with rubber gaskets or the metal/rubber composites just a bit of light grease to keep the rubber sliding not binding when it's tightened; I try real hard not to use cork gaskets for anything. I only use rtv at the corners where 3 surfaces come together (manifold corners, front cover/oilpan/block, etc.) or on machine surfaces where no gasket is required (like the tranny tail shaft housing to the main tranny housing) and even then all it takes is the thinnest smear before tightening.
    #11
  12. mustang90

    mustang90 Founding Member

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    permatex high tack doesn't like to stick to chrome water necks, so you should use a little rtv on the chrome with the gasket so it doesn't leak.
    #12
  13. 89 Saleen#455

    89 Saleen#455 Founding Member

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    Here's a little tick I learned from my dad regarding thermostat alignment. Get yourself a piece of wooden dowel slightly smaller in diameter than the thermostat housing bolts. Cut two pieces of the dowel 2-3" in length. Insert each of the dowels inside the bolt holes on the engine side of the thermostat housing. Take your gasket, and SKIM coat both sides with RTV...please read once again....SKIM COAT. Align the bolt holes on the gasket with the wooden dowels. Slide the gasket over the dowels and align with the back of the Thermostat housing. Place the thermostat in the front housing and twist clockwise to snap in (I use the motorcraft thermostat that snap in). Align the housing bolt holes with the dowels and slide the housing over the dowels and align. Press the housing firmly againt the gasket. Reomve one dowel and start threading the bolt by hand. Do the same with the second bolt. Torque both bolts to spec. and wait two hours for the RTV to set-up before cranking the engine. Never lost a single drop of coolent following this procedure! Good Luck.
    #13
  14. Michael Yount

    Michael Yount Advanced Member

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    Designed properly, it's the gasket itself that does the sealing. As the fasteners are torqued, the gasket compresses into tiny surface imperfections filling all the gaps. Dressings such as High Tack or Hylomar are there primarily to ease disassembly and clean up for the next gasket. If it takes a gasket and rtv to seal, then the either the surfaces are improperly prepared, or clamping forces or tightening patterns are incorrect -- and sometimes that's indeed the case.
    #14
  15. xplhavoc

    xplhavoc New Member

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    Thanks i found out that the thermostat itself sliped down a little causing the leak at the bottom. This time i used silicone to hold teh thermostat in place and used a very thin amount on both sides and took the time to make sure it did not slip. So far it looks good..
    thanks guys
    jeff
    #15
  16. xplhavoc

    xplhavoc New Member

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    Nope now i find out it is leaking not from the thermostat but the main part of the motor. Is this easy to change? Its a gasket..?
    #16
  17. IndyBlk5.0

    IndyBlk5.0 New Member

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    I think that the gaskets you get from napa with the adhesive on the back of them work just fine... Really easy to put on and no danger or mess. And yes, desconnect you bypass line and main line too, they both get in the way, better to have room to work with with you mess with gaskets...
    #17
  18. Michael Yount

    Michael Yount Advanced Member

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    Jeff - there are a number of places on the front of the 'engine itself' where coolant can leak. The front cover gasket, the water pump/front cover gasket, the back cover of the water pump, the upper intake manifold, the water pump intself, any of a number of coolant hoses that attach to the water pump and t'stat.
    #18
  19. xplhavoc

    xplhavoc New Member

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    thanks well it took most of the day but i changed all the gaskets on the front from the themostat to the engine and change the crank seal..
    No problems now. And check the intake wich was not to stight and had a small leak do to it.
    thanks for all the help
    jeff
    #19

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