Gasket Sealant on Thermostat?

[SirMichael]

I did a bunch of testing on my 2GM20F Yanmar engine for a coolant leak. I sealed up the inner tube of the heat exchanger (after cleaning) and pressurized it and immersed in water, no leaks (looked like new inside and out) and also put the end caps back on the engine after removing the heat exchanger, using some home made flat rubber gaskets. I also put a hose between the fresh water input to the water output and bypassed the hot water heater, and removed the coolant input hose (on top) and used a 1 1/4" plug to seal that off. Using an air valve (like from a tire) fitting and a gauge, I pressurized the engine and found that there were no leaks. It held pressure just fine (Just a VERY slow leak down, probably from one of my fittings).

So, I'm starting to re-assemble. I ordered a new set of gaskets, but I'm concerned that the thermostat gasket doesn't appear to cover the top outer edge of the thermostat to hold it down. Like, with the thermostat in place (down in the slight groove) and the gasket over the top, you can remove the thermostat without it touching the gasket. I've done auto repairs in the past and the gasket always seemed to have a hole in the center for the thermostat, where it covered the outer edge of the thermostat.

I'm wondering if I should use some sort of gasket sealant around the thermostat and gasket...

There was no sealant around the gaskets of the heat exchanger when I removed it, so I probably won't use any around the rubber and other gaskets there.

While I was in there, I also removed the exhaust mixer and found that other than a thin layer of soot, it was pretty clear. I have a new gasket for that as well.

Mike

 

[centerline]

when you tighten the bolts for the t-stat housing and add water, it will snug it in there as the lip of the gasket swells slightly.

 

[TomY]

I did a bunch of testing on my 2GM20F Yanmar engine for a coolant leak. I sealed up the inner tube of the heat exchanger (after cleaning) and pressurized it and immersed in water, no leaks (looked like new inside and out) and also put the end caps back on the engine after removing the heat exchanger, using some home made flat rubber gaskets. I also put a hose between the fresh water input to the water output and bypassed the hot water heater, and removed the coolant input hose (on top) and used a 1 1/4" plug to seal that off. Using an air valve (like from a tire) fitting and a gauge, I pressurized the engine and found that there were no leaks. It held pressure just fine (Just a VERY slow leak down, probably from one of my fittings).

So, I'm starting to re-assemble. I ordered a new set of gaskets, but I'm concerned that the thermostat gasket doesn't appear to cover the top outer edge of the thermostat to hold it down. Like, with the thermostat in place (down in the slight groove) and the gasket over the top, you can remove the thermostat without it touching the gasket. I've done auto repairs in the past and the gasket always seemed to have a hole in the center for the thermostat, where it covered the outer edge of the thermostat.

I'm wondering if I should use some sort of gasket sealant around the thermostat and gasket...

There was no sealant around the gaskets of the heat exchanger when I removed it, so I probably won't use any around the rubber and other gaskets there.

While I was in there, I also removed the exhaust mixer and found that other than a thin layer of soot, it was pretty clear. I have a new gasket for that as well.

Mike

I just replaced my engines water pump. A little research found a sort of split on the use of sealants, or not. So I added a good sealant, and mounted it. It leaked,... Some tricky plumbing, I had a hose fitting leaking so I couldn't tell if the pump was leaking at the gasket. I took it all off, got some quality gasket material, designed for coolant, and cut my own(the one that came with the new pump was toast).

I researched more deeply and came upon the gasket material website. This question came up repeatedly, and the answer was always the same, "No, please don't use sealant. This gasket is designed not to use sealant" or something like that.

I also found a proper hose reducer that was leaking. Put it all back together with the gasket I cut, no sealant. Guess what, no leaks.

 

[SirMichael]

I did get around to putting the engine cooling system back together yesterday, but the only place that I used any sealant was on the bottom of the round gaskets (with a cross over that goes between some of the tubes of the heat exchanger) to keep the gaskets from moving as I inserted them. I only put it on the bottom side, not a critical gasket.

I did call the place that I bought the tstat and gaskets from, and asked about the thermostat going through the gasket and basically got mixed answers. The guy I talked to, rechecked and it is the right part number, so he talked to a mechanic who said it is the correct gasket, even though the tstat goes through the gasket. My hope is that there is a little bit of leakage to allow the water to flow through, keeping the air bubble from forming below the tstat.

I put in the larger round rubber rings around the heat exchanger and got everything together. I haven't put antifreeze in yet.

Thanks for the insight on the hose fittings.

Mike

 

[NYSail]

I always fill the engine with coolant prior to adding the tstat..... gets most of the air out as the tstat is the highest point (on my past three boat engines). Also the tstat goes through the gasket and sits in a slight indentation..... no gasket under or on top. The gasket is just for the housing. And never have used sealant.... gasket is designed to swell.
Good luck

 

[SirMichael]

NYsail,
That’s a great idea, I wish I had done that. I have the Tstat installed already though...