I heard Castrol GTX 10w-40 for summer for my 2000 Range Rover from one Land Rover mechanic, yet the dealership is using Mobil products. What do folks here recommend, and how would I go about getting real comparison data?
I ran Rotella T 5w-40 in my '95 Range Rover. No problems, although Chicago does not have heat like Tucson area. I also ran 10w-40 & 15w-40 with no problems in the summer. I used the 5w end to help w/ cold weather starting, but you probably do not have that issue. I did not notice any performance benefits between brands.