<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by taaboo:
Excellent posts by all. With all due respect, very little science though.
<recommends oil analysis comparisons>
Ever wonder why the oil companies haven't done this (or released the results): "Based on our testing results, we find longer drain intervals to offer owners no substantial decrease in the performance or longevity of their automobile engines. Please, buy less of our oil by extending your drain intervals". Yeah right.
I believe that AMSOIL does in fact make
this recommendation. And no, I'm not one
of their pushy independent reps! In fact,
I don't use nor have ever used AMSOIL.
Used to use Castrol synth. They have lately
reformulated so that it's no longer a pure
synth and is now a very well processed
hydrocracked mineral oil. Moved to Mobil 1
instead despite the higher cost. Have run
oil analysis using 7.5K drain intervals
and am happy with the results.
I would bet that the greedy Exxon mgmt
will be shortly reformulating Mobil 1 into
a less capable product now that the two
companies are merged. When/if that happens
I'll move on to something else.
BTW I know two pro lubrication engineers.
They both run synth exclusively. One does
extended drain, one does not.
My belief is that much of the extended
drain capability is due to reduced blowby
of soot and contaminants. Synth has much
higher film strength at the ring to cyl wall
interface, so less crud is blown by into
the oil. Of course, if your rings are shot,
this won't be applicable.
In my experience: yes, synth will leak in
an older engine. Dino oil bakes to a varnish
on the inside surfaces including gasket
mating surfaces. The gasket dries out behind
this false seal. Adding synth can cause the
varnish to be dissolved away over time, and
the dried-out gasket then can't do the job.
Presto, you get a leak.
Switch to synth early on, preferably before
50K. If the engine has had faithful dino oil
regularly with good quality, it would likely
be OK up to 100K. Anything overheated or
undermaintained, don't switch. Use dino on
a short schedule until it dies.