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Water pump gasket sealer?

mherrcat

Contributing Partner
The water pump on my M-18 engine has a metal backing plate behind the impeller and a paper gasket between the backing plate and the pump body. Does that gasket need some sort of sealant applied to it? If so, what type? (Same question regarding the thermostat gasket.)

The reason I ask is I removed the pump cover to check the impeller and replace the hose barbs. I did not use a sealant on the gasket and now I am noticing some green corrosion on the outlet side of the pump body. The inlet side has none. I did put a new O-ring in the pump body and used a pipe sealing compound on the hose barb threads.

There does not appear to be water leaking/dripping, but it looks like the gasket may be wicking moisture to the outer part of the body. I have some extra gaskets so I can replace it easily.
 

Frank Langer

1984 Ericson 30+, Nanaimo, BC
Mark,

The mechanic who helped replace my fresh water circulating pump (not the raw water pump) coated both sides of the gasket with Hi Temp Red Silicone, available at most auto parts stores. It says on the tube that it is a sealant and an adhesive. When I mentioned to the mechanic that I would have just put the gasket between the pump and the block, he said he always uses something like this sealant when water/coolant is involved.

When I replaced the impellor in my raw water pump this past spring, I smeared some regular water resistant grease on the cover and the housing, put the paper gasket on top and screwed it on. It hasn't leaked a drop since then. When I took the cover off to replace the impellor, the gasket came off very easily so it hadn't had any kind of sealant before, and there was a bit of green corrosion from past drips on the cover.

In summary, I think a sealant of some kind is a good idea. The Hi Temp Red Silicone is cheap and dried to a rubbery consistency. I don't know how it would be to remove it as I haven't had to do that, but I would think it would come off quite easily like regular silicone with some kind of scraper/pocket knife.

Frank
 

Emerald

Moderator
A little sealant is often not a bad idea, but if everything is clean and still true and the cover is tightened evenly, you should be able to achieve a good seal with the original style paper gasket (the factory did). The tightening sequence can have a big impact. Never tighten a single screw, and never work around the edge of something in a circle, but a sequence of running in the screws in gently and working across, so following a clock dial as a guide, we'd tighten 12, then 6, then 1, then 7, then 11, then 5, then 10, then 4 and so forth until you've come full circle, and then repeat, each time bringing it in a little tighter. This will make sure you have even seating and hopefully get a good seal. Now, all that said, I've become a big fan of Permatex Ultra Blue for sealing things like cam covers on vintage aluminum engines, which can be a real bear to keep sealed due to thermal expansion. This stuff works well on water pumps, housing covers etc as well, so if you've torqued the cover down evenly and you have some weeping, a little Ultra Blue (or many of the other silicone sealers available) might be the way to go.
 

mherrcat

Contributing Partner
Thanks! The water pump has only three bolts so it's either clockwise or counter clockwise; not much other choice. Thermostat only two. I'll try some sealant. Looks like the thermostat had some kind of grey sealant at one time.
 
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