On Sun, 07 Jun 2015 16:59:04 +0100, Jim at the Common Riding wrote:

For the price of even five litres of mineral (so cheap) oil, why risk
it?
Just chuck it on freecycle or in the lawnmower or even take it down the
tip.

but I have 50L of it !!!

Ah...

the engine is a 3.8 V6 ford essex (canada) manufactured 1995

You might be better off asking in a North American group, then, where
they've actually seen that engine.

and is prown to head gasket failure

Can't see the difference being particularly significant to HG life.

TBH, in something of that era and understressedness - especially given
the age of design - I'd probably be quite happy to just do it - but I'd
want to find out if there was a particular reason that viscosity was
recommended. 5w30 is REALLY thin for a '90s lump.