Roland writes:
Date: Sat, 30 Jul 1994 11:20:34 -0700
From: Roland Dudley <cobra@cdc.hp.com>
Subject: Carnivorous Oil
...I got to thinking (oh oh) about the recent synthetic oil
thread. As I mentioned in my earlier post the differential in
my 289 Cobra needs new seals. The reason for this is because of a
worsening leak at one of the half-shaft outputs. Actually this
diff has leaked ever so slightly for years, but has become much
worse during the last few months. I don't know why this didn't
occur to me during the synthetic oil discussion but I'm
wondering if this might not be the result of having replace the oil with
Redline synthetic about a year ago. Maybe the Redline is
eating away the gunk that's been keeping the oil in for the
past 30 years, but the old oil looked clean coming out and I
didn't notice any significant residue. Of course any gunk might be as hard
as
a rock and glued to all of the interior surfaces so maybe detergent
action is the culprit. On the other hand maybe this stuff IS
eating the gaskets and seals.
Anyone else have a similar experience with synthetic oil in a diff
or transmission?
Roland
Yes, I'm having the same experience with the TR6 differential in my '76 TVR
2500M. The car getting on in years, but only has 11k original miles on it. I
went through lots of deliberations also about using synthetics in my cars.
I've accumulated some interesting stuff about synthetics along the way.
Synthetics looked like good stuff, and a very good idea where applicable. The
only concern I was left with was this question of seals. Not that synthetics
would consume or damage seals, but I was left with the issues that Roland
mentions above. That less supple, aged seals with very fine cracking at the
lip, plus the tendency of synthetics to remove deposits, and not leave deposits
themselves, would result greater fluid loss pass the seals.
On my 2500M, I finally decided that I would change just the gearbox and diff
oil to synthetic. When I got the car, the differential was weeping a tiny
bit. Now, since I've changed to synthetics, also Redline, the weeping has
increased quite a bit. The fluid loss isn't huge. The diff is down about an
1/8th of a quart every 2K miles or so. The transmission, however, hasn't
increased it's fluid loss, and is effectively not weeping any fluid (though I
check all fluid levels regularly).
I think, though, that I may have made a slight mistake here myself. When
confirming the proper fluid weight for the car, I checked a handful of sources,
the TVR lube plate, the owners manual, and the Haynes TR6 book. The fluid
recommendations were a bit varied. I went to the light side and think that if
I ran a 90W/140 I'd see less weeping. I'm going to try this.
Just an observation about synthetics. At 70 degrees F, synthetic lubricants
pour much, much differently than a petroleum oil of the same viscosity rating.
A 20/50 or 75W/90 Amsoil or Redline is dramatically less "thick" than the
equivalent petroleum oil. And, when they're hot, synthetics also appear to be
"thinner" then they're petroleum counterparts. Even synthetic greases will
flow at room temperature.
I've got an informative article on synthetics that was forwarded to me from the
hot rod list. It can help with a decision regarding synthetics. It's about 4
pages long, so it's a bit lengthy to post to the this list, but if anyone would
like it, I'll be glad to send it to them.
- Steven
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