Ever since I bought my XJS I've been using premium fuel in her. I know regular fuel is recommended, but have any of you used premium. Am I just wasting money? I feel it couldn't hurt and probably runs better. Anyone have an opinion on this? Thanks!

 

What year/engine is the car ?

My 92 V12 states clearly in the owners handbook, on the instrument cluster beside the fuel gauge, and finally on a little plaque on the inside of the filler cap that it must use Premium unleaded. I wouldn't put anything other than Premium unleaded in it. It's temperamental enough as it is...... :-)

 

I have always used Premium. My manual recommends premium. ....I once used filled a tank with regular as had heard many use it on their XJS's, but will never again do so. There was what I would call a noticeable difference in performance. I do not think its worth the whole 6-8 dollars in savings per fill up. If I really want to save on gas I ll get a Prius (God forbid)

 

Depends on the model - later models with Marelli have a jumper in the engine bay to alter ignition maps for both premium and regular. I use premuim 98.

It all comes down to tuning - higher octane fuel among other things allows more ignition advance before detonation hence more power. If you have a car setup for regular fuel with mechanical or vacuum advance running premium is not going to get you any gain.

 

You would be wasting money since no significant gain would be made using premium gas. I remember as a kid putting premium gas ocassionally in my 1954 Chevy convertible and thinking...boy I am really flying now...only a mental vision and not reality.
I purposely have my XJS slightly retarded to be able to run 89 octane gas. There is no pinging at all even when I floor it. I probably am giving up a little in power, but I drive the car almost everyday and economy is an issue for me. Not all Jaguar owners have or want to spend the money on premium gas every fill up. My car is dependable and not temperamental at all. It has some issues to sort out like most do, but I know what they are and the list is getting smaller. Like anything else, it is a matter of choice and I choose to be economical and use the savings to buy more new parts.