Ohmster

It is July 4th and the car is under the carport cooling off. I want to replace the thermostat and thermostat gasket today and don't know whether or not to put blue silicone gasket sealer on the O-ring type thermostat gasket or not. The car is a 1995 Honda Civic EX. The gasket really looks like a rubber O-ring with a small rubber flange on the inside of it with small rubber pegs to line it up properly. I have a green stain running down the back of the engine and need to add water to the cooling system every two or three days or the engine will overheat. The stain begins under the thermostat housing, car has 142K miles, and to the best of my knowledge, never has a wrench been put to the thermostat housing bolts. Time to change the gasket I guess and might as well throw in a new thermostat while I am at it.

So, do I need to put blue silicone gasket sealer on this gasket or since it is a neoprene rubber O-ring, just clean area and skip the gasket compound? I want to do this in the next few hours, a quick answer and I would be much obliged. Thank you.

93egred

DO NOT PUT ANYTHING EXCEPT THE GASKET ITSELF IN.....NO GASKET MAKER NOTHING.....just clean both the surfaces off the gasket will be touching very well

Ohmster

Ooops! Wish I had seen this earlier. Well, I think we found the leak, at wast!

Had water disappearing from the cooling system and car would overheat every 2-3 days with low water. Saw a green stain originating under thermostat housing and ran down back of engine. Bought new gasket and thermostat. Took off old one today and guess what? No gasket and no thermostat! Just a bead of black silicone all the way 'round the housing and that was leaking. You could see the stain of hard water scale on the back side of this "make your own gasket".

I brushed off the scale with a steel brush and cleaned it up good with acetone and then put in a new thermostat and gasket. Took a while to figure out how the gasket and thermostat go in since there was no old one to study when I took it apart. Seems that the thermostat slides into a groove in the O-ring gasket and that entire assembly slides right into place in the engine block. Since I did not get my answer in time, I put a thin bead of blue silicone on the gasket, installed it, then another thin bead on the housing and installed that. Bolted it on tight, put everything back, and filled with coolant. The old housing was not too corroded or anything and I got most all of the scale off so I probably could have skipped the silicone. Since I did not know I figured that it cannot hurt and that blue stuff is really good stuff so put it on, won't hurt anything.

We will see now if it leaks anymore or not. Here are some pictures to show you what some knucklehead installed instead of a gasket. Look how the water ran right under this "gasket" and out the engine.

CivicSpoon

I'm pretty sure I put some silicone sealant stuff on mine when I replaced it (Mitsubishi Silicone to be exact, their version of Hondabond). It's been on there for a year or 2, and I've never had a problem with it.

Ohmster

Yeah, that's what I want to hear, thanks dude. Didja see the pictures? No doubt the water was coming out, right there on the back of the pure silicone make believe gasket. Thanks for the input!

ef_88_hatch

all you need to do is clean the housing and the head really good put a very small amount fo sealer on the housing just to hold the rubber seal in place and be sure not to over tighten or it will leak.