Short answer, premium fuel for the XK8.

If in an unusual emergency, only regular is available and your about to run out, the computer will compensate for the lower octane but it shouldn't be used regularly.

 

Definatly only premium in any jaguar.

It's only 20 cents a gallon more dude, you must be pretty cheap to even ask this question.
That would be like me saying if my air filter was removed, but I wanted to save a little money, could I drive without the filter.

 

WHAT! I didn't even know leaded fuel was still available. LOL! I wouldn't use it, but then again I know nothing about it. I'd stick with premium mate.

 

Even though I am not (yet) a Jag owner, this type of question frequently shows up on various car sites I visit, and it especially cracks me up when it appears on sites catering to high performance and/or luxury cars. My answer is always "do the math". Here in SoCal, the difference between regular and the highest premium is maybe 20 cents a gallon but let's say it is 30 cents for argument's sake. If you do 10,000 miles a year and get 15 miles per gallon, that ends up about 650 gallons a year. So if it costs 30 cents more for the premium that ends up just under $200 for using the premium. If you are looking at cars in the over $30k price range, is $200 even worth worrying about?

Doug

 

Congrats on moving up! Yeah, you're nuts if you run it on anything other then premium. Given you live in the US take the average $.20 diff between regular and premium and mulitply it by 20 gallons ( i dont think any jag holds this much, maybe hte XJs) and thats $4. If you cant afford $4 you prob shouldnt own a Jag lol. Plus, even cars that can run ok on regular that recc. premium get signi. worse gas mileage and performance... therefore it actually costs you more to run it on reg then just buying premium up front. This doesnt even take into account how shitty it is to drive and the extra wear and tear on the car. Moral of the story: If your car recc. premium USE PREMIUM

 

The higher quality (and higher octane) gas the better. I question whether or not all the premium sold around here is really premium.

 

Well, if you use BP ultimate, and keep your receipts as I do, BP guarantees any repairs done to your fuel system. Of course, you do have to prove that the issue is gas related and that you BP ultimate the very high majority of the time. To be honest, I haven't used any other gas in the last 4 years. Only twice have I had to use the premium from chevron because BP ran out of gas during the hurricane.

 

I try to buy gas from only one local gas station because I've found that when I dodge around that is when I have performance issues.

 

I have regular access to 100 Low lead aviation fuel. How would this affect performance in my 2000XKR?

 

It would lighten your wallet, which would improve acceleration.

Seriously, unless you've modified the engine in such a way as to require higher octane, I can't see how there would be a significant performance improvement. Once we have enough octane to prevent knocking, higher octane really doesn't do much.

Oops, forgot this part ... lead is lethal to cat converters.

 

I expect to be flamed upon receipt of this post, but heck, it's winter and a little cool in Atlanta.

I've been running my 2001 XKR on regular gas for the last three years. There is a slight performance degradation (I've gone from wicked fast to really fast) with no perceived loss of MPG and absolutely NO fuel issues of any kind.

Call me cheap (go ahead, I'll wait) but I think it's a reasonable response to ever-escalating fuel costs. I STILL have the fastest car in my neighborhood, and am the envy of my friends. I have to be a pragmatist about this car...it's not a concourse car, it's just a great looking, very exclusive ride. And I love it. That said, when I next need new tires, I shall eschew the $350 Michelins and find something cheaper from Kumho.

Living life in the (pretty) fast lane,

Dave in Atlanta

 

Dave,

No flame here, but I would have this concern.

When we run a lower octane than the engine design calls for, knocking (detonation) will tend to occur under certain load conditions. There are sensors on board to detect this and reduce throttle (maybe adjust mixture or timing too ... not sure) to stop it, but these can only go to work after some detonation has occurred (the sensors work by listening for an acoustic signature that says "knock").

So, whether detectable by a human ear or not, there's probably some detonation going on in your engine, and this can be pretty hard on components in there.

FWIW. What do you think?

 

Not sure how it happened, but SnakeSkinner above seems to have wound up with my Garage! (The old '90 Fleetwood was the tip-off) I don't really mind, as long as he puts a coat of wax on everything before he brings it back.

A glitch in the system?

 

100LL has an unacceptably high amount of lead in it which would kill the catalytic converters in no time flat by plugging them solid. Count on a 1-3K repair bill or more.

A higher octane rating gas than specified by the OEM will NOT increase mileage, performance, starting, hair on your chest, appeal to women or any of the other hundreds of myths that won't die.

Octane lower than specified may reduce performance and mileage if pre-ignition is encountered as the knock sensors and computer will back off the timing accordingly. There is no hard evidence to substantiate the engine damage theory on engines so equipped.

 

I do not know of any gas stations that offer leaded fuel!

Since the engine and internal components were designed in 2001, it has a specification for fuel type and octane. If you are on flat ground or going down hill, you probably will not notice any difference

Here in California, we have mountains, so with a lower octane, we would probably notice a difference!