I got my 2003 S Type free, and it's approaching 110,000 miles. It's only used around town and I don't care about performance. I'm starting to consider not using premium as prices go up.
What about you?

Nope, for the extra $6.00 to fill up in Joyces Jag.

Now my daily has a 34 gallon tank and he gets the premium too. Yep 2 credit cards to fill him up!

That is why I have the subaru.

If you don't care about performance, stop using it irrespective of price. Gas is over $5.75 per US gallon in my area of Canada for 91 octane- been over well $5.00 for a long time.

It is $3.85 a gal here in Ga. for 93 premium. Since I run high boost of course the extra 5.00 or so is a must, I have been running 93,100,116 ect... in different cars so long its just part of it. The price of going fast.

My truck and stuff that dose not have to have it then no way I use it.

Hmm, I know it doesn't help you much, but just to put things into perspective....

Over here in the UK albeit on diesel fuel ( A little more expensive but you get the idea ) we're currently paying £6.55 per UK gallon which equates to $10.37 approx.

You say you're paying around $5.00 which in UK terms would be about £3.16............man, I'd pay that in a heart beat and be pleased about it

Nope, I just drive less.

I also use gas from Costco. It was $3.87 for 93 octane and $3.65 for 87 (3/4/12). I waited in line with a lot of people buying premium, about 15min. It seems when the price of gas goes up, Costco seems to be cheaper than usual. I guess they are trying to boost their memberships.

I consider the cost of a blown engine and then just suck it up and pay it. Oil companies got you my the b@ll$. Dont really have a choice you want to drive you need gas. If it gets that bad get a beater. I just ride my bike get 45 mpg on it so when the gas prices go up car just gets driven less. No big deal saves miles on it anyways.

I always use premium, you do realize that's like an extra 20 bucks a month right? If you have any kind of a decent job, that should not matter what so ever. I doubt it would hurt it though...as long as you are not redlining the motor all the time. Whatever you do, don't use regular in the supercharged motors.

I'm kind of screwed, all of my vehicles are premium only. My beater has a Northstar V8 engine with 10.3:1 compression stock, so you absolutely need to use it. I have a GMC Denali 2500 HD that uses Diesel and costs over $150 to fill up the tank, the 2 Jags, Vette, lol. My gas bill is about $600/month.

I'll pay the extra $5 to fill up every week or two. $200 a year isn't going to make enough of a difference. And it wouldn't really matter unless premium was more than 30-40 cents a gallon above the price of regular. Either way I'm still paying that same difference. Now fouling out the cats might make a bit of a dent in the wallet...

The XJR does just fine on major brand regular.

++

The XJR 4.0 or 4.2?

BTW, what would be (gradually?) happening if it wasn't OK?

4.0

The ECM will adapt to the octane rating. Other than that, there shouldn't be any other effects.

It is sometimes postulated that premium returns more MPG so that the additional cost is offset by that factor.

Interestingly enough, there is a enthusiast who is/was also the head chemist for a major oil company. He switches brands every 6 months or so because, according to him, the additives in the differing brands are more effective at cleaning the deposits left by other brands. At his level, an employee is issued a company card for gas purchases. So, his practice costs him money and he still does it.

I use the mid-grade and it works just fine for me. I did some tests using premium and didn't notice a difference.

The 4.0 has a different PCM and sensors doesn't it? What evidence is there that the S-Type PCMs will adapt to fuel which is of lower octane than the minimum specified? AFAIK: none. You'd be just hoping it does. So, what if it doesn't?

BTW, the car was essentially developed here (UK) I believe. Such low octane fuel is not sold on forecourts here so would not be convenient for Jaguar to use for testing.

Just add Techron to your tank in small amounts! Your only missing detergents.

Unless the design of the PCM is completely different than contemporary practice at the time of release, and is less capable than its predecessor, there is good reason to believe that it does. There is also the factor of personal experience. One is expected to be intelligent enough to detect signs of incompatibility and to make personal choices to respond suitably to the situation.

To state the converse, there is also no evidence that there is an absolute requirement for premium fuel or the long term effects of using premium fuel. There is one exception. The oil company chemist referred to in the earlier post does say that the additional volume consumed by octane additives takes away from the volume usable for detergent additives. He should know, as he is the one specifiying the compounding.

BTW, the UK uses a different octane rating system. The same *real* anti-knock qualities can and do have two different octane *numbers* under the the two different systems. And then there is the practice of using references like "regular" and "premium" which have very nebulous meanings unless the precise octane rating and octane rating system are also specified.

I know about the different octane systems, covered in similar threads before. Our minimum is 95 RON (about 91 AKI I think).

The PCM changed from a Ford unit to a Denso unit and doesn't even use the same CPU family so was rewritten. Maybe it was written to cope with octane below the minimum. Maybe not.

I'm quite happy that people stick in whatever they like but seems to me there are reasons why Jaguar specify what the minimum is and second-guessing may not be at all wise.

Second guessing the manufacturer is the raison d'etre for enthusiasts.

Otherwise, one could stick to reading the owner's manual and be done with the whole thing. There would be no need to post on forums or discuss anything at all. Take it to the dealer and accept everything spouted by the service advisor as the gospel truth direct from the heavens.

The problem with manufacturer recommendations is that sometimes they need to be read with a lawyer's perspective since they are designed in some cases to reduce manufacturer liability.

There are plenty of posts on the forum of people that use regular fuel in their home market. However, there is (probably) not one post where any ill effect other than the loss of some ultimate raw horsepower can be directly attributed to the use of regular fuel.

If one were to only stick to manufacturer specifications, then there ought to be no question that every single car should still be on Pirelli's in the case of X308's, and whatever the original fitment was for the S-Type.

As tires are directly tied to safety, then it would be less wise to second guess on tire selection than fuel. The same goes for brake pads and shocks. Yet, these choices are applauded as "upgrades".

Nah, you're going overboard!

Regular in effect is 95 RON (91 AKI) here.

Petrol octane such as 95 is the same now as it was in 1999 etc. Tyres have improved with new technologies. Not many would really argue that the original version of the Pirellis would be ideal now. (I guess the OE pads are as bad for dust now as they were then LOL, but stop the car OK)