Do I have to use the Castrol edge professional 5w-20-a oil that meets wss-m2c925 spec if I am only changing the oil every year and I only put less the 2k miles on it or can I use a Castrol full synthetic 5w-20 that meets wss-m2c945 spec

 

....... and Here we go Again..........

 

I don't think you will find a definitive answer or consensus here, or anywhere else on the internet. There are thousands of posts on that subject. Get the specs, compare them and make your own decision. That is what I did. Here is a summary of my comparison of what I deemed the more significant differences:

1. Piston skirt varnish - 925 spec = 9.0 min, 945 spec = 4.0 min
(I don't know why you would specify a minimum instead of maximum or what the units are, but those are the specs)

2. Cam + lifter wear um - 925 spec = 20 max, 945 spec = 60 max
(this is the one that bothers me the most)

3. Average engine varnish - 925 spec = 8.9 minimum, 945 spec = 7.5 minimum

4. Viscosity increase at 40 C - 925 spec = 90% max, 945 spec = 150 % max

While many of the requirements are the same, many cannot be compared easily in the specs. Example: the 925 spec refers to elastomers as RE1, RE2, RE3, and RE4 and the 945 spec calls out the actual material such as Silicone Rubber, Polyacrylic Rubber, and Nitrile Rubber.

 

I don't want to let Dave down so I'll give a definitive answer. Use it or you will die.

 

But what about the important bit (the car)?

 

Use what ever you want.

 

My little heart goes out to all those "never to be read" owners manuals.
Not to worry Draguar poster. Were it not for oil and battery threads this Forum would dry up and blow away, says me. Everybodys got to start their Jag experience/education someplace.

 

Brilliant post!

 

On a XKRSGT why use the best or even do more than necessary.
Use the easiest option, what do you have to lose.

 

Draguarxkrsgt, if you hang around here long enough you will learn to ignore most of the comments and posts made by people with nothing better to do. I, like most others have. People tend not to bother posting on this forum due to their snide remarks and then the chorus of clowns complain that the forum is dead. Really. Remember, some of these comments are coming from people who say a certain a tire brand will kill every one that uses them, even though he is, evidently, still alive and so are the 50 million other people that use them. Plus others on hear that swear i-phones are the work of the devil. Take them with a pinch of salt.

Regarding your question, use the factory oil. You can purchase it from Ebay or the dealer for about $10 a quart. Not worth risking the engine in your fine car for the sake of $90.00 in oil costs.

 

Yep, I'll cop to the bad behavior and a bit of humor, though my joke was with Dave and not meant to be directed at the OP. I can see how the OP could have perceived it that way however.

Dave already provided the real info so I decided to have some fun. Apologies to the OP.