Rear Main Seal - Silicone vs. Fluoroelastomer

[Kenneth B.]

Hello, folks,

This inquiry is directed to the SBC engine gurus and engineers:

Just read an interesting article in the current Corvette Restorer by John Bissell regarding the two different rear main seals available for the SBC - Fel-Pro parts #2900 (silicone, blue) and #2912 (fluoroelastomer, red), wherein the author espouses the superiority of the red #2912.

Can someone please explain the difference in formulation that supposedly makes the 2912 so much better? Is this superiority a documented fact, or merely an opinion?

And finally, since I haven't yet buttoned up my bottom end on my 327/300, should I pull out the 2900 I just installed and replace it with a 2912?

Thanks in advance.

[Joe L.]

Re: Rear Main Seal - Silicone vs. Fluoroelastomer

Hello, folks,

This inquiry is directed to the SBC engine gurus and engineers:

Just read an interesting article in the current Corvette Restorer by John Bissell regarding the two different rear main seals available for the SBC - Fel-Pro parts #2900 (silicone, blue) and #2912 (fluoroelastomer, red), wherein the author espouses the superiority of the red #2912.

Can someone please explain the difference in formulation that supposedly makes the 2912 so much better? Is this superiority a documented fact, or merely an opinion?

And finally, since I haven't yet buttoned up my bottom end on my 327/300, should I pull out the 2900 I just installed and replace it with a 2912?

Thanks in advance.

Ken-----


The fluroelastomer seal is better. Period. The silicone rubber seal is "old technology" for this application and is, essentially, obsolete.

GM apparently agrees with me. The last GM silicone seal was GM #473424. It was discontinued in January, 1994 and replaced by GM #10121044 which is the fluroelastomer seal. So, you haven't even been able to buy a silicone seal from GM for over 14 years.

Should you change your recently installed seal? That's a tough call. I think I might just leave it the way it is and see how it all works out. If there's no leak, you're "home free". If there is a leak, you can change it to the new seal. It's really not all that much more difficult to change the seal with the engine installed in the car, so you don't lose a lot by waiting.

[Kenneth B.]

Re: Rear Main Seal - Silicone vs. Fluoroelastomer

Joe,

Thanks for the prompt reply.

The motor is currently sitting on an engine stand with the pan removed, so I think I'll go ahead and change it; no time like the present.

If the fluroelastomer seal is so much better, I guess I'm surprised that the silicone seal is still available, especially for such a potentially troublesome application. For an extra ten or fifteen bucks, it seems to me like a no-brainer.

There must be some reason it is still manufactured and marketed...