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Water Leak on my thermostat housing of my 240z

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just removed the thermostat on my 240z, cleaned it, cleaned and sanded the thermostat cover thus removing all dirt and grime. once reinstalled with new thermostat cover gasket and tightened the bolts took the car for a drive and noticed there is a small wáter leak. Is this normal? I am also looking for a 71 C (160 F) original nissan oem thermostat but havent had any luck yet. Mine is 76.5 C thermostat (Tropical weather). Any clues on how to prevent the wáter leak? should i also sand the housing?

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Not normal for it to leak.  Don't use a grinder if you sand, it will cause uneven spots.  As long as you take off the old gasket and or sealer you should be good to go.  Did you try tightening it a bit?  If it was not leaking before, then it should not leak.

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I use Permatex Aviation form a Gasket number 1.  It is non drying and of a pasty texture ideal for sealing not perfect mating surfaces.  Water, fuel etc compatible.  Apply to block and thermostat housing surfaces, sandwiching the gasket.  Advice to clean up the seating groove is right on target.

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I'm a purist and I would just surface both gasket surfaces and then use Gasgacinch on the gasket. If you want to use RTV, you should still make sure the surfaces are straight and clean.


Today's RTV selection is pretty impressive. Plenty of new engines don't even use gaskets anymore.


For oil applications I use "The Right Stuff" brand black RTV.


If I don't want to see the black (like on a front engine cover), I use grey RTV.


For exhaust I use the high temp orange RTV.


For water, "Threebond" brand  "liquid silicone gasket" (1211) is my pick, but most of the others will work just fine.

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