re. 20v urq: Synth or semi-synth?

[Ben Swann]

[For my friend's 20v urq, we'd like to know what's better, synth or
semi-synth oil? Particular weights recommended?
Also, the bomb appears to be dead...only 2 pumps and that's all folks! hard
as a rock afterwards! The Pentosin level appeared to be around the MIN
level, could this have an effect on the bomb's operation? DO we need to
flush the Pentosin? How to do this correctly?

Thanks for all your answers and help,
Mihnea]

As much as I'm an advocate of Synth and my favorite is Castrol Syntec 5W50,
my experience with the Blends has not been positive.  Go with straight dino
or synth, and even OK to mis them, but for some reason, the synthetic blend
did not seem to hold up any better than conventional, in both marine,
chevy, and VW/Audi motors I used it in.  If I recall, it especially was
more prone to high temp hard running operation eg. Boat running close to
WOT continuously - the stuff tended to thin out like water.

My results with Syntec have been nothing but positive, despite the
additional cost.  You can extend the change interval without worrying about
it, and use it year round.

This is just my datapoint to add - YMMV as usual.

Ben