RTV needed?

other_shoe · Aug 13, 2010

I'm replacing my thermostat and tried to do so without using RTV sealer. It leaks, which leads me to believe that sealer is necessary. I'd very much appreciate comments if there is something else I should do besides adding the sticky stuff.

Celeb · Aug 13, 2010

I've always tossed the gasket and just used a very thin bead of ultra blue rtv and giving it plenty of time to dry. Never had a leak using it and have done it probably 6 times between my cars/friends car etc.

I like using the rtv personally because if you ask me, you can clean/sand/prep all you want but the rtv helps seal the imperfections in the mating surfaces (if you have any)

ForceFed70 · Aug 13, 2010

If it's a chrome housing, throw it out and buy a replacement with an O-ring seal. Even if you get it sealed it will continue to haunt you later.

68stang351 · Aug 14, 2010

ForceFed70 said:
If it's a chrome housing, throw it out and buy a replacement with am O-ring seal. Even if you get it sealed it will continue to haunt you later.

+1, they are leaky junk.

Personally, I use a very thin coating of Ultra Blue silicone on both sides of the gasket.

Pony66 · Aug 14, 2010

Just use a Fel-Pro gasket and some RTV on both sides. You dont need too much. Also put a little dab on your bolt threads. Dont overtighten. Snug it down, let the RTV set up and then retighten. Of course make sure the thermostat is in the correct direction with the spring on the engine side and the little bleeder valve at the top.

other_shoe · Aug 14, 2010

Bleeder valve? I'm not sure what I'm looking for there.

And, thanks for all the helpful responses.

rbohm · Aug 14, 2010

what i do is take the paper gasket included, and coat both sides with a thin coat of #2 permatex or black rtv, either way works well. i then assemble the part and give it a little time, usually ten minutes, to set up before i put coolant in the system. doing it this way i have never had a leak in 35 years, and on a variety of vehicles.

zigmont · Aug 14, 2010

Leaking housing

The reason most thermostat housings leak is because they have been overtorqued and the mounting ears are bent down. If you set the housing down on a flat surface you can see a gap under it (the housing).
To correct this, I clamp the housing in a vise and file the surface flat again. It is pretty easy since the housing is aluminum. Once you are finished, a very thin coat of sealer will do the trick. And don't tighten the housing down too tightly or you will just warp it again. 5-7 ft lbs should do it.
If you don't want to file the housing, you can place a sheet of 100 grit sandpaper face up on a hard flat surface and rub the housing on it until it is flat again.

My $.02

other_shoe · Aug 15, 2010

Thanks for all of the help.

When I got the leaking one apart it was clear why it was leaking. The thermostat had slipped out of place and was digging into the bottom of the gasket. When I did it again yesterday, I used RTV on the housing side of the gasket and then put the thermostat in place and mated the gasket to the housing. Then I let it sit for a couple of minutes so that things would stay in place as I fit it up with the manifold. Then I put the sealer on the manifold side, bolted the housing in place, and then came back in an hour to retighten.

Good tip on not overtightening it, Zigmont. Luckily, the water pump kept me from getting too much on the lower bolt, and I didn't go tighter on the upper.

68stang351 · Aug 15, 2010

other_shoe said:
Thanks for all of the help.

When I got the leaking one apart it was clear why it was leaking. The thermostat had slipped out of place and was digging into the bottom of the gasket. When I did it again yesterday, I used RTV on the housing side of the gasket and then put the thermostat in place and mated the gasket to the housing. Then I let it sit for a couple of minutes so that things would stay in place as I fit it up with the manifold. Then I put the sealer on the manifold side, bolted the housing in place, and then came back in an hour to retighten.

Good tip on not overtightening it, Zigmont. Luckily, the water pump kept me from getting too much on the lower bolt, and I didn't go tighter on the upper.

This is how I always keep the thermostat from slipping down. Next time take a rubber band, and loop it through the thermostat, then place the thermostat in the housing and pull the band tight through the water neck and insert a screwdriver or pencil or whatever to keep the rubber band tight and it will keep the thermostat in place. When you are done, just pull out whatever it was you inserted in the band on top of the water neck, and pull the rubber band out. I do it that way every time and have not once had a thermostat slip.

other_shoe · Aug 15, 2010

Great tip with the rubber band since it was still touch and go with my approach. Thanks.

RTV needed?

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