Motox71

I just attened my first Corvette Funfest in Effingham IL. While there I went to a seminar called: C5 Common Repairs and Q & A by Corvette tech Paul Koerner. In the course of my question about an issue I had with my differential, I told him I had changed my diff fluid using Royal Purple. Before I could finish my complete sentance he loudly and passionately told me to "GET IT OUT!" Said he has seen it lead to an overheating failure of a particular washer that will cause it to become a one legger among other things. He was dogmatic about me only using: Dexron LS 888862624

I plan to do as he instructed, trusting that he is a very experienced and well respected Corvette Tech on C5-C7's. I just wonder whats so bad about the Royal Purple? It has the friction modifier in it already. And since I first changed it using it I haven't had any issues. I have probably put at least 1k miles or more on and have had it up to 140mph a few times. Im assuming if RP is so bad, it might have failed by now. Nevertheless, I trust his expertise's more than mine and I have ordered the Dexron LS and will be changing as instructed.

What are your thoughts?

Grandpa1

Does the Royal Purple meet the specs?
If it does tell him to go blank himself if it doesn't then change it.

CorvetteBrent

I see no reason to doubt Mr. Koerner's claims of encountering overheating washer problems with the Royal Purple. Why would he lie about it? He has way more experience than I do, so I would follow his advice to use the Dexron. Thanks for the post. I learn the wildest and most interesting things in this forum!

leadfoot4

There have been a couple of differential discussions, with pictures, here in C5 tech, over the years. I seem to recall the mention of a "Belleview spring" or washer, that is known to sometimes crack. However, I don't recall ever hearing about any other part being all that fragile, in the C5 diff, and/or it's demise being caused by a particular gear lube, or it's preservation attributed to a particular gear lube. I would hope that any possible difficulties that were caused by using one brand of gear lube or another, would cause some sort of audible indication of the trouble. I've has Red Line's gear lube in my 2001's differential since 2002....

SaberD

I could see how using the wrong fluid could cause higher operating temps. I have and always will use the gm fluid. The belleville washers are basically spring washers that keep a preload on the clutch packs in order for the limited slip to work properly. Although TBH about every c5 that has more than 75k miles probably has at least one cracked belleville washer if it hasn't been replaced already. They are a very weak component to begin with, so adding more heat to the mix would certainly cause premature failure. I replaced mine with higher strength aftermarket washers.