I run royal purple in all my rigs. Put some in my 03 discovery and it runs and sounds great.

 

I ran RP 15w40 for a couple changes. Worked well for me. Never did figure out the ZDDP content. Any idea?

 

I like RP stuff, not using their oil in the LR's but they do make a diesel 15/40 weight. Just kinda hard to beat the Rotella stuff. I've used their PS fluid, and gear oil for years with great results.

 

I don't know about the zddp. I have use RD for years. Coast more but Werth every penny. I changed oil in a ride after 15 months of driving, looked the same as the new oil. Don't do that but it happens

 

Here is an oil anyalis on royal purple 15w-40 from a ford diesel truck. Hope this helps. I use rp hmx in my work car due to the high zinc in it and if you get their racing oil (not avaliable in a 15w-40 though) it has the added zinc also.

 

I prefer redline and was going to do a complete fluid swap in the next month (tranny, dif, engine)