I will offer just one last suggestion. What you actually do is up to you because it's your vehicle. Were you to get a toothache, and you visit the dentist, the dentist would prescribe some type of antibiotic to you at a certain strength along with a number of times to take it per day to create enough anti-bodies to "overcome", Subdue and eradicate the infection.

Well, if he prescribes 500mg's taken every 4 hours for 5 days, how smart would it really be to purchase a prescription at 200mg's every 4 hours for 5 days?? In this scenario, you may never product enough antibodies to "KILL" the infection. In the case of your vehicle with it's supercharger, "with prolonged use", you might actually do something to degrade some operation over time.

My recommendation would be do what is prescribed, and you'll likely mitigate any probability of something going grossly wrong as a result of saving a few dollars here or there. Again, just my suggestion.

 

Well, to use your analogy, the dentist (Jaguar Owner's manual) prescribes 91 AKI/95 RON fuel. Would you, as a lay person patient, second guess your professional and use 600mg's (93 AKI) instead of 500mg's (91 AKI)?

Works both ways.

 

I do believe my manual has a similar reference so I commend you on the fact. My manual also specifies "Premium Grade" with those numbers which I take to be any fuel that is deemed Premium as opposed to regular. It's really neither here nor there. Personally, I'll spend the few extra bucks and look to avoid any possible mishaps.

 

I think you've hit on the specific cause of some or most of the confusion- lack of consistency with assigning names to the various octane levels of gasoline/petrol.

The cars are apparently consistent worldwide- full performance is achieved with 91 AKI/95 RON.

This gas is called 'regular' in Spain where Jorge is.

It's called 'super' or 'premium' or 'high test' where I am, but 93/94 AKI is called 'ultra-premium'. 89 AKI is called 'mid grade' or similar.

In the high mountain areas of Canada and the US, I've heard that the same 89 AKI is called 'premium' or 'super' etc. as cars at high altitude don't require as a high an octane rating.

I'm not quite sure what gas is labelled in your area.

Everybody confused yet?

 

LOL, I'm in the suburbs of DC (Rockville Maryland) and gas here is really has only one fuel cost and it's known locally as Expensive as "He__" double hockey sticks no matter the octane.

An interesting observation also, is I use Sunoco fuel. As of most recent, they've stopped selling the 91 octane and most have only 93 now. I think most of the Shell Stations in this region are doing the same thing. I guess greed is really good and apparently very legal now too.

I know I've gone out west to Arizona and on 10 headed west or east, especially in New Mexico, there are stations that have ethanol based fuel and octane of 85... WT_??? I actually wondered what I'd do for fuel out there with My Jag or my E55 benz.

The answer was to leave my eaton supercharged A4 out there as it'll drink anything and be happy..

 

Tequila!

 

I can certainly appreaciate the need for higher octane in a supercharged engine. But I have to wonder about it with our V6. Does Ford require premium with this 3.0 engine. If not, what's the difference between this and Ford's version?

 

I agree, Tequila will solve any problem, at least temporarily

Serious answer is that if the owners manual were more explicit, they would go on to give fuel requirements for high altitude owners, meaning that full performance would be achieved using 89 AKI and maybe even give a chart and graph to quantify 'high altitude' and show octane rating vs. barometric pressure. Naw, that's not going to happen.

The ethanol fuel/E10 issue (actually non-issue) could have been better explained too, but that would give us one less thing to repeatedly thrash here. 'Course maybe that poor dead horse could use a day off now and then.

 

Mechanically - cylinder heads, intake, exhaust, and variable intake valve timing.

Electronically dunno. I know my 2.5 in my old X-Type demanded premium, which I found to be, uh for lack of a better term, dumb.

 

It may be connected with the fact that here (where the cars are designed etc) the lowest readily-obtainable is 95RON, roughly your 91 AKI. We don't call it Premium (being the lowest, you can see why).

Electronically, the redesigned S-Type (2002.5MY) uses a PCM that Ford don't generally use (it's also in the X-Type and other jags).

Jaguar may have tested (I suppose, in the USA where such fuel is) to see what happens if you run lower octane, or they may not.

Our Premium (not always called that) is 98RON or higher (101RON is occasionally obtainable).

Sadly it looks like we scared Jorge off, which is a pity as his car looks to have a fault we might have helped him find/fix.

 

Thanks for answering that guys. We won't be using it daily so not that big an issue. FWIW, 91 would be mid grade here and maybe a nickle cheaper.

 

I only read the first and last page...There has been great debate and what most come to the conclusion is that running a lower octane won't hurt anything unless you run at WOT...I had a non-R 4.2 and could hear loud pinging at WOT using E10 87. Not good. This isn't an one size fits all, additives can vary from gas station to gas station and the station can change their additives without notice. You really need trial and error to determine if your car, (year, country of origin, tune) with fuel (additives w/ or w/o ethanol) makes any difference in MPG...

 

This debate is amusing. Regardless that its a few bucks more I put what is required in the tank. It says premium, so premium it gets. If I wanted to save money on fuel prices, I would of bought a damn prius and turned my smile into a frown along the way.

 

LOL, win!

 

This question never goes away does it?

 

The question is: what is premium and what is not? Apparently the "standard" gasoline in Spain (95 ron) is equivalent to premium in some places and "premium" in Spain in 98 ron.

Also, as probably most here know, "premium" is a marketing trick. The real difference is the octane in the gasoline, which is a measure ONLY of how much the petrol can be compressed before it self ignites. It is NOT a measure of quality, but of compresion, or what is the same, additives that makes it more compressible, nothing to do with cleaner petrol or similars.

If your engine doesn't have a high compression ratio then high octane petrol is a waste of money. And the STR has a lower compression ration than the standard V8 4.0L....

It could be argued that for the difference in price (which is some countries is significant) why not to put "premium" (i.e. high compressible petrol) but if the STR doesn't need it at all due to its lower compression ratio it is a complete waste of money that could be better used in something else.

Do you fill your swimming pool with bottled mineral water? Money is to spend it well, not to waste it

 

Not scared off! Just was too bussy to return!

But you scared me now about the fault! Can you explain more? please!

 

You don't really understand how engines work if you think the STR doesn't run best with a higher octane fuel. Also, here in the USA gasoline is formulated in a lot of different ways depending on the region you live in and the time of year.

Now there's the alcohol that's added and what a mess that can be. The stupidest thing they ever did for energy policy in this country. Less energy by volume, screws up a lot of cars and using good food producing farm land (plus another petroleum based product fertilizer) to make fuel for our cars. Just dumb.

 

But, Jorge is in Spain, and as he noted in his post, *his* regular is 95RON.

It's not about understanding, it's about perspective.

And ... if *a* particular engine does not ping or retard under *any* circumstances on a particular grade, then that grade is the optimum grade for *that* particular engine. Oops, "octance rating". Because as astutely pointed out by JagV8, premium is not the same thing in all geolocations. The only thing consistent about "premium" is that it carries a "premium" price.

 

It's been so long that I've no idea what it was you posted and I'd rather not hunt through all the posts so please start a new thread describing whatever it was

Ah - found it. You just did