Can anyone guide me please. Lots of work being undertaken on my P38 to make it near perfect and I am now going to fill it with oil.

Up to now it has been using a 10/40W with regular changes, no oil loss or leaks etc

I am now being told to use one with a zinc/phosphate additive as the older style engines like that. Millers oils rings a bell.

However that has adverse effects on the catalytic convertor apparently. Should I be more concerned about moving parts or that expensive cat?

I, along with a few others on here use valvoline vr1 oil which is 20W50
The zddp degrades the performance of the cats which is why is not in newer oils. It's fine for roller lifters, not the ones in the v8

2 schools of thought on this I think:

1. A New CAT is cheaper than a new engine or a major engine rebuild so bung an old "high Zddp oil in it to prevent wear.
2. LR altered the valve-train design slightly to remove the "flat-face" issue so their recommended multigrade W/O Zddp is just fine.

I'm sitting on the fence on this one, but my common-sense says LR must have addressed the issue in order to go "Cat-Friendly" because Cat's were becoming mandatory.

I'm personally not aware of any change, a flat lifter is just that, I dont see what changes could be done, but I'm not an engineer and happily proven wrong.
LR also leaned the running, increased the temp and used a thinner oil for better emissions too but that doesn't mean its not detrimental to the engine. I'll wager LR did nothing to address the issue, I don't know how to check, but I'll wager the same lifters are used in pre-cat vehicles
who said anything about common-sense?

I run this..


You want Zinc in the Oil to protect the Cam and Tappet, which on Flat tappet valvetrains can wear to a heavy degree without Zinc.

The lack of Zinc in modern Oil is to protect Cats and the thinner viscosity is to aid in fuel consumption.

Internally the Rover V8 from 1965 is the same as one in a 2000 P38 - the main difference being the change from Dizzy to crank driven pumps, the latter is more efficient especially in pumping thicker oil..

In practice a RV8 with run on anything, but i'd opt for a 10w50 - 10w60 or 20w50.

Almost all oils found in the above grades are Racing spec which is full of zinc, which will extend the life of almost every component in your engine, well the ones ed with oil!!

Some people will say the Cam is made of cheese, however ANY flat tappet valvetrain will suffer with the wrong oil..

I also have an x Reg 4,6 and I am bound to get others questioning my reason. My beast is parked up for 8 to 9 months a year due to working away a lot and does minimal miles in the few months on the road. However I change the oil and filter each year before start up and fill it with Castrol GTX 5W30 Magnatech and so far no issues, it is a V8 4.6 Thor the god of thunder 112000 miles, plus i have had the beast for about 8 years now and runs like a dream. (damn just cursed myself with the RR gods) any good oil is good but also mine is used in the cold conditions of Russia so thats the oil that is good for me.

Thanks all...I think I will go with the ZDDP oils and hope for the best. Great shame I can't get around the cat problem but hopefully I'll give up before the car does.