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Old 12-05-2008, 10:26 PM
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Stupid thermostat housing gasket

I've got a 1993 F-150 with the 4.9L 300 cu. in. inline six cylinder engine. A year and a half ago the thermostat housing gasket started leaking. Not wanting to fiddle with it I removed it, cleaned both surfaces perfectly, and used good ol' RTV gasket maker to seal it up. I let it cure overnight, topped off the coolant and everything was wonderful. About a year later it started leaking again.

After the RTV failed to work a second time I went through about 4 gaskets and bought a new housing, as I cracked the old one, not sure if it was me or I just expanded a crack it had. Anyways, putting the gasket in dry leaked. Using Permatex gasket sealer on both sides of the gasket (sparingly) leaked. Using Permatex only on the housing side of the gasket worked. I also made my own gaskets out of heavy paper gasket material. The store-bought thin paper gaskets didn't do any good.

Now, about 6 months later, it is leaking again! The head side of the sealing surface is machined smooth. The housing is a cast finish, that's why the sealer on the housing side only seemed to work.

Anyone know what kind of magic is required to seal this thing so it doesn't leak? I can build a whole engine but I can't seal a stupid thermostat housing. What the heck?

There is a small heater hose nipple that comes into the housing and there is a small hole cast through the housing for the flow. This hole is off to the side of the thermostat and I don't like this design as there is nothing to provide clamping force on one side of this small hole.


Thanks for any help.

Steve

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Old 12-06-2008, 12:50 AM
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Use this on both sides of the gasket and don't try to kill the bolts. Just snug 'em down good. I've replaced the stat on my 92 4.9 and never have experienced a leak.
http://www.permatex.com/products/Aut..._Sealant_a.htm
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Old 12-06-2008, 01:52 AM
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May also take file and see if it's flat or warped, if so file flat then use the sealant. I've had many that were warped from someone over tightening the bolts.
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Old 12-06-2008, 08:26 AM
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Quote:
Originally Posted by SSedan64
May also take file and see if it's flat or warped, if so file flat then use the sealant. I've had many that were warped from someone over tightening the bolts.
yes your right with the file and not over tightning the bolts
thinner gasket better , your mashing the ends with bolts being tight and causeing the houseing to warp
this is like headers , there swelling and swrinkage do to temp changes
which pushes the gasket out .
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Old 12-06-2008, 08:37 AM
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Always had good luck with Permatex #2 - have never tried the #3 stuff.
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Old 12-16-2008, 08:22 PM
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Thanks for all the replies guys. Yeah, I was using good ol' #2. Maybe I will try #3 and see if that can pick up the slack.

I took a file to the new housing just to be sure the sealing surface was all level.


I don't have a torque wrench to do the inch pounds that are spec'd. Cracking the housing by over tightening is a big concern. I tried just snugging them real well.....whatever that means to me. I think my wrist has some calibrating to it.


Steve
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Old 12-16-2008, 08:54 PM
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Quote:
Originally Posted by Aussie XAXB
I've got a 1993 F-150 with the 4.9L 300 cu. in. inline six cylinder engine. A year and a half ago the thermostat housing gasket started leaking. Not wanting to fiddle with it I removed it, cleaned both surfaces perfectly, and used good ol' RTV gasket maker to seal it up. I let it cure overnight, topped off the coolant and everything was wonderful. About a year later it started leaking again.

After the RTV failed to work a second time I went through about 4 gaskets and bought a new housing, as I cracked the old one, not sure if it was me or I just expanded a crack it had. Anyways, putting the gasket in dry leaked. Using Permatex gasket sealer on both sides of the gasket (sparingly) leaked. Using Permatex only on the housing side of the gasket worked. I also made my own gaskets out of heavy paper gasket material. The store-bought thin paper gaskets didn't do any good.

Now, about 6 months later, it is leaking again! The head side of the sealing surface is machined smooth. The housing is a cast finish, that's why the sealer on the housing side only seemed to work.

Anyone know what kind of magic is required to seal this thing so it doesn't leak? I can build a whole engine but I can't seal a stupid thermostat housing. What the heck?

There is a small heater hose nipple that comes into the housing and there is a small hole cast through the housing for the flow. This hole is off to the side of the thermostat and I don't like this design as there is nothing to provide clamping force on one side of this small hole.


Thanks for any help.

Steve
This can be a real pain, usually when the thing is tightened the ears under the fasteners bend down. Eventually it leaks and you tighten the fasteners a bit more increasing the bend. Eventually the housing breaks. The trick I use is to use a washer inside the hole that passes the fastener that is just a little thinner than the gasket or O ring, which ever is used, This keeps the fasteners from being run down so tight that the housing bends under the force but still allows sufficient crush on the gasket to seal the interface.

Bogie
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