ianellison

Why the difference in the recomended intervals between the UK & USA,

Back in the early 1990's there were only mineral oils and mineral oil
mixed with 'cracked' oil to give a wider viscosity range typically 10 -
30, 15 - 35 or 20 - 40.

We can now use synthetic oil with a wider viscosity spectrum (I use
Mobil 1 15-50 Motorsport which also has a 1200 ppm lead level good for
our cars). These oils, I believe, are far more stable and degrade far
less under heat and pressure than the old mineral oils.

So, the BIG question is, what would Porsche have recomended - or what
interval is really needed between oil & filter changes using our modern
oils??

dfinnegan

The best way to determine your oil change intervals is to send samples in for analysis. Blackstone Labs, for example (no affiliation), will tell you how well your oil is protecting your engine and, thus, how long you can continue to use it.