I Have A 91 454/b1 And Was Wanting To Use Synthetic. I Was Told By A Mechanic That If I Start Using It Now It Will Leak From Every Seal.is This Something That I Should Worry About.

Sounds like urban myth to me. Where's his research and data coming from?

I THOUGHT THE SAME THING THATS WHY I AM ASKING THE EXPERTS.

HE CLAIMS THAT IN ALL THE OLDER MOTORS THAT HE HAS SEEN SWITCH TO SYNTHETIC HAVE DONE THIS.

I doubt EVERY seal will leak. I have "heard" that synthetic may leak through seals.

If your motor is stock, don't bother switching.

Your Mechanic is dead wrong. Ask him to explain why. Guarantee he has no real explanation.

I don't fully understand this however I can tell you that I run synthetic in my 1989 454 bravos without leakage.

I use synthetic gear oil in my 72 SS Chevelle M22 transmission and it leaks through the side cover. It never leaked with conventional gear oil. I don't know if this is related to the particle sizes or surface tension, but I know from experience it leaks in the tranny.

bbcngineer

THE MOTOR IS STOCK UNTILL NEXT WED. IDECIDED TO GO WIHT 502 ALUMINUM HEADS, MARINE POWER ALUMINUM MANIFOLDS SND RISERS, 750 HOLLEY, MSD, AND A NEW CAM. I THINK THIS SHOULD PUT ME AROUND 450-475HP. WITH THESE UPGRADES SHOULD I USE SYNTHETIC AND WHAT WOULD BE THE BEST SEALS TO USE.

I had about 175,000 miles on my 94 GMC 1/2 ton pickup with a 350 in it when I tried synthetic. Yes, it seemed like it was leaking badly out of every seal on the engine. I know that there was some seepage before the change but now it was leaving puddles instead of a few drops here and there. I changed back for that very reason. I did, however, change the grease in the differential to sythetic with no leakage at all. No urban myth, just my own experience............and that's all I have to say about that.

Roger

Synthetic oil typically isn't as "thick" but has superior lubricating properties hence it will be given higher viscosity ratings. That's why sometimes the seals leak. In a sense, if you had a leak before it may get worse because the oil is a little thinner. You can make the same thing happen by switching from a 40wt oil to a 5W 30.

He is probably blowing it out of proportion but there is a "little" truth.

Thanks I Will Give It A Shot,hope I Don't Have A Bilge To Clean Soon.