TOPIX is reasonably cheap, if you decide you need it.

 

Nice skating, and you've dodged the subject at hand completely. Fuels sold here (with very few exceptions) all contain ethanol and have done so for 20 or 30 years depending on region. This includes the top tier brands you recommend. Jaguars built from the 1990s onwards (the models we're discussing here) were built with E10 in mind. What happens with antiques, if anything, or racing cars is irrelevant to the OP's question.

E10 contains ~97% of the energy of 'pure' gas- making a ~3% difference in fuel consumption that most drivers never notice.

All fuel off goes 'off' at more or less the same rate. The fuel retailers you hold in high esteem disagree completely with the time scale of 60 days your propose and state 180 -365 days if kept in a sealed container (like a car's gas tank) depending on whom you ask.

Please stop dragging out myths and half truths as though they're fact. We've beaten them to death far too many times here.

I've had full access to all SAE documents since October 31st 1978 and contributed to several in a professional capacity during my 31 year career with a major (world's largest in it's class) engine OEM. You may have read some of these very papers.

As you seem to hold them in high regard, thanks for the compliment.

 

Here's my problem...

You two guys are obviously very experienced in the disassembly, inspection and repair of engines, but your views on fuel seem almost diametrically opposed. My 10 years of experience as a Process Engineer and Chief Chemist at the refinery of a tier-1 oil major was over 20 years ago, so I'm going to discount it, except to say that I did oversee the actual octane test engines with variable compression to force test fuels to detonate, and I could see that low-octane fuel would detonate sooner than high-octane fuel as compression increased.

But all that was a long time ago, although even today I seldom hear anything to the contrary. In addition, it's my understanding that alcohol is mildly but cumulatively corrosive, methyl alcohol (methanol) more so than ethyl alcohol (ethanol) unless the engine and fuel seals were specifically designed for use with fuels containing alcohol.

Just to be sure, I check my Jaguar S-type manual. On the subject of octane, it says:

"The preferred fuel should have an octane of 95 RON (91 AKI) unleaded fuel... Using unleaded fuel with an octane rating less than recommended can cause persistent 'spark knock'. If severe, this can lead to engine damage".

On the subject of ethanol, the manual says:

"Most drivers will not notice any operating difference with fuel containing (up to 10%) ethanol. If a difference is detected, the use of conventional fuel should be resumed".

So, Jag says 91 AKI fuel is better than 87 AKI, and my guess is that 94 AKI might give even better performance in a high-compression engine under load. In addition, Jag would seem to prefer fuels without alcohol although, maddeningly, they won't state exactly why. However, a check on possible reasons for failure of the Viton seals in the pulsation dampers on the fuel rail will provide a clue.

For the time being, until you guys can agree, I'm going to stick with Chevron 94 AKI for my STR, especially as it contains 0% ethanol.

 

Absolutely true. And that is the ONLY difference between the various octane ratings. Nothing to do with 'quality' or volumes/types of other additives.

Again true with the emphasis on 'mildly'. It's important to understand that E10 is 10% ethanol and not methanol. Cars built prior to the early 90s were not necessarily built for ethanol blended fuels. Cars built since then were. No need to cower in fear of Satan Ethanol even though it is a political and ecological disaster.

Again correct and the first quote contains the answer to the OP's question. Less than recommended octane CAN cause detonation. Keyword is CAN.

Does it in real life? The question has been asked and answered on this board many times. The overwhelming majority (I won't say unanimous for obvious reasons) can find no evidence that it does as would be witnessed by reduction in power levels, increased fuel consumption, audible signs of detonation, physical engine damage, etc, etc. The earliest S-types are now 14 year old cars with mileages well over 200K, some 300K. If use of low octane fuel were to cause problems, that's plenty of time for them to have surfaced.

The same comments apply to use of E10. Jag says resume use of conventional fuel if a difference is detected. First- that's not an option for many owners. Second- most drivers notice no difference.

I'll attempt one more time to explain the flaw in your logic.


In the octane recommendation from Jag you quoted above, the concept they are putting across is that low octane (87) fuel may permit detonation to occur, which would in turn might damage the engine. To avoid this, they propose using 91.

Your logic is that if 91 is good, 94 is better. For 94 to actually be better, it would need to eliminate detonation that is occurring when 91 is used.

Why would Jag contradict their own warning about engine damage by specifying use of 91 octane that according to your logic permits detonation?

Everything I've read here and elsewhere infers that these engines achieve 100% potential (detonation free under all circumstances) on 91 octane.

Similar to the real life experience of owners not seeing any reduction in performance when using 87 compared to 91, owners using 94 have not seen any improvements over use of 91.

Similar to the oil and filters debate, the best advice is for the owners to use whatever makes them happiest.

As for me agreeing with posters that drag out old myths and half truths but nothing to support their positions, not going to happen.

 

Well, it's very odd that two people with 71 years' experience between them cannot agree on this subject. Your characterization of 1stjagjet's statements as "myths and half-truths" does nothing to promote a discussion of this subject, especially when directed to a relatively new forum member with 40 years experience. I hope that 1stjagjet isn't saying to himself "maybe this forum wasn't such a good idea after all".

In addition, your statement that "these cars can operate successfully with no short or long term damage on regular (87 AKI) fuel... Many owners detect no difference in power levels or fuel consumption, never mind complete absence of detonation" is in conflict with Jaguar's experience with the S-type. It's like saying "the medical profession agrees that cigarette-smoking causes cancer, but I know many people who smoke and (as of today) are cancer-free".

 

On the other hand- there's plenty of real life, everyday evidence that proves a link between smoking and cancer. If anything, the medical community was slow in agreeing with what Joe Average already knew.

Joe Average hasn't yet seen a link between 87 octane and damage to S-types even though there's a growing fleet of vehicles that have exceeded the typical life expectancy of an average car.

If 1stjagjet has got some evidence to back up any of his points, that would be a different story. What happens on race cars, vintage Jags and WWII fuel is of no relevance.

As it stands, every one of his bits of advice and warnings have been previously presented, debated and in most cases resolved. Why drag them out yet again?

Have we run out of steam to debate synthetic vs. dino oils?

 

I'm sure the medical profession will be intrigued to know that Joe Average was ahead of them in establishing the link between smoking and cancer.

I have seen many posts on this forum from members who have reported low mileage and or loss of performance when using 87 AKI fuel, and relatively few (one notable exception) who found no difference whatsoever. Maybe all this info is just "anecdotal" and should be disregarded. Must tell Jaguar they have it all wrong.

 

If 1st stuck to facts, preferably ones relevant to S-Types, it would help. Would sure make for shorter posts...

 

Last summer, my wife and I took a 3000+ mile road trip. Admittedly, we were not driving a Jaguar, but it was a 1997 model SUV with a high compression (10/1), fuel injected engine and automatic transmission. We divided the trip into thirds. We varied the types of fuels used during each part of the trip. We did not test "low grade" fuel (-85 octane) because experience had already demonstrated that this engine knocked very badly with these fuels.

During the first third of the trip, we use "mid grade" fuel (around 87 to 89 octane) from major brand dealers. During the second third of the trip, we used "high grade" fuel (91+ octane) also from major brand dealers. The high grade fuel cost on average 15% more than the mid grade fuel that was available but produced on average 20% better mpg than the mid grade fuel used during the first third of the trip.

The last third of the trip retraced the same route as the first third of the trip. We continued to use the high grade fuel during this part of the trip, but we specifically purchased fuel from non-major brand dealers. Once again, the high grade fuel was about 15% more expensive that the mid grade fuel that was available, and we continued to have the 20% better mpg. There was one exception in the final third of the trip. We had one instance when the high grade fuel purchased from a non-major brand dealer produced lower mpg than we would expect from a mid grade fuel.

The vast majority of the driving during this trip was on major highways at speeds between 60 and 75 mph, and the cruse control was used consistently.

I realize that this is not a truly scientific test, but it made me a believer. I will continue to use high octane fuel in high compression engines during highway driving.

 

Still more non-scientific observations:

Our 2005 S-Type 3.0 has run just fine on regular 89 octane since we purchased it in December 2008 at 18,000 miles, now showing 78,700 miles. No pinging, no stress under load, and my wife was consistently able to get between 33 and 34 mpg on the interstate with cruise control set between 72 to 75 mph depending upon the location and highway patrol presence....

Her 2006 XK8 4.2 runs better on 91 octane than it does on 89 octane. Interstate driving running 89 octane was consistently at 25 mpg for her, while 91 octane now delivers 28 mpg for her. She was able to spot the difference very quickly after we purchased the car, which still surprises me. She always fills it up with 91. I sometimes fill it up with 89 just to see if she will notice. She always does and chastises me for it....

 

Thanks to everyone who contributed to this lively discussion. It has been a truly educational one for me as a non-mechanic. I am very grateful to learn from so many highly knowledgeable, eminently qualified people. A great discussion always involves at least 2 different points of view and this one sure has it. Bravo!

As for my own opinion based on my limited knowledge of how companies think within the context of a very competitive and litigious world...

I would guess that Jaguar's recommendation of 91+ octane has to do with minimizing both engine repairs and customer complaints of poor vehicle performance during the warranty period. I can infer then that 91+ is the right fuel to avoid those issues.

If the average car is driven 12,000 miles per year and averages approximately 22 mpg, it will require 545 gallons of fuel annually; at $3.15 per gallon (~87 octane) it will cost roughly $1,717 per year in fuel to drive 12K miles.

Run the same car with the same numbers but on 91 octane costing 15% more - it will cost $1,975 per year in fuel (or less if mpg improves), for a net fuel cost increase of $258 per year.

For me, the added cost of 91 octane is a reasonable expense to ensure the maximum performance and reliability of, and (hopefully) minimal repairs to, my Jaguar engine.

Why risk shorter engine life or potentially poorer performance with lower octane fuels just to save a few rupees at the pump? My cat purrs like a kitten with the recommended 91. Why mess with success?

BTW - many of the "top tier" brands here charge $1+ MORE per gallon. At 545 gallons per year, that's at least an additional $545 in fuel costs annually for top tier, making them a questionable value compared to the off-brand I buy. Might I get similar benefits from dumping an occasional bottle of Red Line into my tank at considerably less expense?

(for the record: I fueled my car yesterday with 93 octane @ $3.159 per US gallon here in New Jersey at a Wawa convenience store.)

 

Here it's roughly $2 per litre

 

I had no idea that the top tier stations charged a dollar a gallon more. That's obscene.

Rather than putting in Red Line or any other additive, I'll send you free of charge a bag of my patented magic voodoo petrified chicken bones. Just wave the bag in front of the car any time you want to rid it of bad things. We use them extensively up here to make sure the engines start on cold winter days. Sometimes we need two bags.

 

Once again you have truly added to the depth of this discussion with an insightful and useful suggestion for the Jaguar owner everywhere.

Bravo !

I can hardly wait, what's next, VOO DOO or Exorcism ? Never have the facts been applied to the point more convincingly.

I've been reading some of your other posts, Mikey, They make for very interesting reading.

Carry On, as I know you will...

Cheers Robert

 

Jumpin Jag flash......looks like you just about got the answers you were looking for, or more than enough, I'm not sure.

Why is it always oil or fuel that starts these nonsensical posts?

By all means one member can say black and another white, but just do it with some civility please.

Thread closed.