I have a 94 f150 I6, manual. I'm replacing the thermostat with a Motorcraft thermostat and gasket. Do I need a rtv type sealant if the housing is in good shape? I've read a few conflicting write-ups...some say just use the gasket only, some say use rtv with the gasket. Thoughts?

Thanks...

NEC

 

I think it depends on your parts. I have heard some need the RTV because the parts aren't flush. For my truck, I don't need it.

 

I use the blue colored stuff from permatex on most everything. It doesn't harden so much and should make cleaning up easier if it ever needs attention again. I think it's called RTV, comes in a tube like RTVs. I never had anything leak that I used this on.

 

If your using rtv , why use a gasket? You should not need rtv at the thermostat, but use one or the other, not both.

 

I always use the blue silicone,put a VERY light coat on both sides of gasket.
Never had leaks that way

 

Agreed. If anything, hi-tack to hold the gasket in place

 

The gasket should have a sticky side to help hold it in place. I didn't use anything other than the gasket, and do not have any leaks.

 

Never seen a thermostat gasket have a sticky side, not saying they don't make them. It should not be hard to hold the gasket in place, push the bolts thru the housing, slide the gasket over the bolts and start the bolts. I changed water pump and thermostat on my 4.9 about 5 months ago, no rtv, just gaskets. No leaks yet.

 

Just take your gasket and smear a light coating of Permatex No. 2 on each side. It's non hardening and tacky enough to hold your gasket in place, and if you have any imperfections in the machined surfaces it'll take care of that for you too.

RTV is for when you don't HAVE a gasket to work with! Or to fill in gaps like in corners of gaskets where they meet other parts.

 

^exactly, using rtv with a gasket actually increases your chance for leakage.

 

thanks all!!!