Using Castrol Syntec as apparently similar to using the old
Pennzoil, it left the non wear surfaces in my Mustang coated with a
thick film that resembled varnish. Keep in mind I did not know this at
the time. I changed the oil when I got it with the same Syntec my friend
used since the first change. My next change in 3 months was to Royal
Purple. The car had ~58K miles on it, mostly highway, zero mods, never
to the track. Within 6 days or so the oil pressure went down then up
every time I started. The filter was getting clogged, I didn't know this
at the time. When checking the dipstick there were flakes of crap all
over the stick, thus floating in the oil. I immediately had it changed.
told Goober up to thu' station what was going on and they were so
perplexed the gave me a free change. It kept doing it and I changed the
filter myself after almost 3 weeks.

    At this time was when I started to do a lot of research on oil and
on different brands. I also read some info on the Amsoil site and
combined with every thing else I read and and was told by different
people I switched to Amsoil and before draining the RP I added some
engine flush and flushed it well. The problem didn't return after that.
Several years later when changing heads and cam, I saw what was left of
the film on the surfaces of the engine and in the heads. Now I know that
the flakey stuff that was on the dip stick was getting cleaned off by
the RP and clogging the filter. It was finally completely cleaned when I
flushed it really well. I have other stories from other unrelated people
that tell me A) I'll never use Syntec again and B) Royal Purple solves
too much, too fast if you've been using an oil that leaves a lot of
residue.

   Castrol Syntec is NOT a true synthetic oil regardless of the judges
opinion.