CarTalk.com Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

Which sealant to use with valve cover gasket replacement?

I am going to tackle replacing the VCG on my '91 Miata this weekend and have read conflicting information on what kind of “sealant” to use on the six specific location listed in the service manual.

The service manual simply states “high temperature silicone gasket sealant”

I did some research on the web and everybody seems to have differing opinions on black, blue, red, copper, non hardening, plyable etc.

from what I can make out permatex ultra black is the product of choice for this kind of job but not 100% sure.

Any help would be much appreciated

I used red to fasten the two ends of the valve cover gasket to a loose piece that bridged the remaining gap several years ago and have reused the gasket many times in an effort to locate a troublesome hydraulic lifter and to change the timing belt. I have not heard that the type of silicone sealant matters. I did a quick read of a few sealant labels and chose red but can’t recall why.

The high temp permatex was red the last time I used some. If it says “safe for oxygen sensors” on it, it’s good. That means that if some chemicals seep into the oil from the sealant, they won’t contribute to O2 sensor contamination if that oil somehow gets into the combustion chamber.

Sounds like a lawyer wrote that after he became an auto repair guru.

This is what vehicle manufacturers use now that they no longer install gaskets.

http://www.permatex.com/products/our-brands/the-right-stuff

Tester

“The Right Stuff” (Tester’s link above) is a relatively new product and really is the best for containing oil. You don’t need the high temp stuff. The Permatex “Ultra Black” used to be my sealer of choice for Valve Cover Gaskets and “Ultra Grey” for sealing any surfaces where the bolts are closely spaced, i.e. oil pan gasket.

Each of the types of “Ultra” sealants, identified by color, have specific characteristics for specific applications. “The Right Stuff” replaces a lot of them and is actually more oil resistant than the silicones.

That means that if some chemicals seep into the oil from the sealant, they won’t contribute to O2 sensor contamination if that oil somehow gets into the combustion chamber.

It’s actually the gases produced as the sealant cures. These gases get sucked through the PCV system and then into the combustion chambers. Not many products out there anymore that are not “sensor safe” but it pays to be sure.