Hugh, I like Peter Graham use Penrite in my 3-litre. I use their HPR Diesel and have had no issues after a lot of miles. The pressure only drops 5psi between hot & cold even during our hot Aussie summers. I read somewhere in a petroleum engineers report that diesel oil has very good anti-scuff properties, so I figured it would be good for the rocker pads @ cam lobes. Mine are unmarked after regrinding many miles ago.

Hugh, I ran Mobil 1 in my 4.5 for well over a year between 1996-8. It was supplied by Mobil who did a monthly analysis of the oil. The reports were fine and it appeared to have no side effects except the car registered a lower oil pressure — about 30 vs. previous 35. I stopped using the oil when I moved away from the free supply and went back to Penrite. I was running shell bearings and the engine had been rebuilt in 1986. We rebuilt the engine again in 2003 and could see no effects of anything unusual. I had done about 76K miles between the 1986 and 2003 rebuilds. However I can see little wrong with sticking to Penrite which is what I use now and have done almost 30K miles since the last rebuild, it is all OK as far as I can tell.

I might add the 2003 rebuild was a result of other issues and nothing to do with the engine which could have gone back in the car as it was, but we took the opportunity to rebuild it as it was out of the chassis.

I have had two or three collector car owners tell me that they use Mobil 1 in their cars and, based on the Mobil 1 report, I intend to use it in my 3 litre. Can someone who has experience with Mobil 1 address this question in more detail?