what is proper application of rtv sealant

for oil use the ultra black RTV and torque to spec.

 

I've always found the best way to use RTV is to drop in in the trash and select a different product. RTV always seem to end up where you didn't want it. I like permatex 518 on flange type joins like an oil sump if no gasket in used. With a gasket permatex #3 aviation sealant is pretty good.

 

i use the ultra black RTV at woork and on my cars to seal oil it woorks very good if you use a gasket ONLY put a thin coat of RTV.

 

Yes, it seals quite well. The problem is it tends to end up in places it shouldn't be. When the surfaces are clamped the excess oozes out and form a bead, which cures and is prone to come loose and lodge in oil passages. The factories use dispensers to control the amount applied so this doen't happen, but that is hard to do with a tube. On gaskets, it is just so slippery that the gasket tends to be forced out or position when you troque the bolts. 518 is a similar consistancy to RTV, but in anaerobic, so it olny hardens beween surfaces, any excess that oozes never hardens. #3 never hardens completely any where and is quite sticky, so it helps keep the gasket in place instead of forcing it out. The only place I have found RTV useful on the 308 engine is just a very small dab at the corners on the valvecover gaskets where they meet the oring. Just my experience.

 

mk e's statement is right on the money. But I prefer 518 over #3. 518 works well with or without a gasket. Ferrari switches back and forth from 518 to silicone and the motors that they put together with silicone have more problems with oil leaks.

 

a thin coat will not be a problem

 

Aviation sealer is a good gasket dressing, but don't put rtv on gaskets or o-rings. Hylomar is good for o-rings since it stays gooey. Stay away from 'the right stuff' in the whipped cream can. Its a fix all type of sealant, and it dries too fast. Good for plumbing, or caulking the driveway. not cars.

 

I've used all of the sealants.

I agree with the others, RTV is dangerous if slightly abused.
RTV has to be used very carefully, just enough so that a bead is barely becoming visible on the outside of the seam. Also, I try to not put any past about the middle of the seam so that there's less towards the inside of the seam. This minimizes the chance of a substantial RTV bead being on the inside of the seam where it can break off & cause trouble.

I do use RTV as a gasket dressing by smearing a thin film on the mating piece, then placing the gasket in place, pressing the gasket into the RTV, then wiping any excess off.

If in doubt, I'd use Hylomar instead of RTV, but it too needs to be used sparingly.

518 & 519 anaerobics have their places also. I tend to use them on fairly clean surfaces & RTV on surfaces I can't seem to get all of the oil off of as it seems to displace the oil better.