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Thermostat housing leak

bobct

Advanced Contributor
So I got everything back together and started her up for the first time since Nov. Intake manifold gaskets and trans rebuild seem good so far just running on the hard. It would have been a total home run except my thermostat housing is leaking... again.

Starting about three seasons ago, I've always had a little puddle of coolant on the intake manifold. I changed the thermostat, new gaskets and still leaked. Pulled it apart, new gaskets and same thing. I think I tried 2-3 times but just lived with it. This time I ran a thin bead of RTV around the gasket avoiding the metal rivets (the leak is the lower part of the housing to intake section, not the upper half). I always clean the surfaces nice and smooth.

Sure enough it immediately had drips coming out. I tried torquing a little more but no change. I'm sure I can fix this if I run a thicker bead around the perimeter but would have to ignore the rivets. Since the sender is mounted higher, does it matter if the rivets are covered in RTV on the lower gasket?

Do they make a thicker gasket that will compress more? I do notice a gap between the housing and manifold but they feel like they mate up dry.

Bob
 
2X on ensuring the gasket surfaces are FLAT...smooth is nice but FLAT works.

Covering the rivets will impede their function so I's suggest not covering them...and RTV shouldn't be needed with the proper gaskets...

If the leak still hangs around, the housing may have a crack...
 
Craig,

I was thinking the same thing. Ok, I guess I need to remove it and make sure it's flat. I think if the housing had three bolts instead of two that would help.

Bob
 
THat's a thick piece of iron. I don't think 5 bolts would fix a warped housing. Plate glass, wet sandpaper is the ticket. Like MM says, check for crack first.
 
Here's how to "glass plate" that housing:

Buy some machinists bluing (thin, fast drying spray paint).

Spray the mating surface and let the paint dry thoroughly.

Slide the housing back and forth on rough sandpaper duct taped to a pane of glass. Be sure to keep in FLAT while doing this, rotating it every few strokes about 90 degrees each time.

Turn it over and note the shinny areas; those are high spots. Hit them lightly with a right angle grinder and repeat the above.

You may have to go through the above a dozen times, but if you're careful it will be very flat when you're done.

Jeff
 
Craig,

I was thinking the same thing. Ok, I guess I need to remove it and make sure it's flat. I think if the housing had three bolts instead of two that would help.

Bob

I actually used gaskets without the rivets on one of my engines and never had a problem with sending unit or temp gauge.
 
Update, my leak is fixed. I was going to resurface the upper and lower sections but decided to just order two new ones. I'll rework the old ones and keep them as spares. In addition, I got a hold of the Permatex #3 and all is well.

No way to know if the Permatex or the new parts did the trick. This leak was preventing me from putting my wet bar back which is blocking my next project. I had to get it right the first try. BTW, the new lower thermo housing is slightly different now. A little higher and has two add'l threaded ports which I capped with the included plugs. Same part # though (97452).

Bob
 
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