Read post #53 by Doug in particular point 1) and the following post written by myself. The answers are all there. Try some high octane for fun and tell us if you (honestly) see a difference.

 

Why would you buy a performance sports sedan and not run what the manufacturer suggests? Makes no sense. I have been driving 4.0 and 4.2 S-Types and XJ's for 8 years. Your injectors will probably need more work if you cheapen the fuel too.

 

Thanks for the reply, I saw his post, but it had waaay too many words with seven or more letters for me to understand. I did notice that he said "retard" though, that was a pretty fun time.


Soooo to confirm, as this falls under the category of better safe than sorry IMO, no harm can be done from using a certain type of fuel for 12 years and then switching to a different one, correct?

 

As do many.

But are we making the car feel better or making ourselves feel better?

I run only high octane top tier fuels and wayyyy over-maintain my Jaguar. I KNOW it makes me feel better. I'm never completely sure, though, if the car knows the difference.

Cheers
DD

 

And again- there's NO connection with octane ratings and quality!
Ever wonder why cars built for 87/low octane don't suffer from fouled injectors?

 

I spent many years in the engine business, have had my hands on thousands of engines...no Jaguar engines though. There always seemed to be less carbon buildup with 91+ octane fuels, always had the nice peach/pink tone on the valves, etc...with a touch of tan on the plugs if mixture was correct.

However... my wife's 07 Tahoe with the 5.3 has never run differently with 87 or 93 octane. My 06 Colorado with the 3.5 was the same way... plugs were fine either way. Now, my 69 Camaro certainly runs better with 93 and would likely ping with 87.. old school tech though.

I could probably get away with 89 octane on the Jag but for pennies per tank why would I? Forced induction engines always run a higher risk of combustion chamber issues, especially in hotter weather so why chance it? Without knowing more about compression ratios, chamber design and boost profiles I can't speak intelligently about it on our 4.2 R's but I'll keep 91+ from name brand producers such as Shell, Chevron, etc and not worry about it.

 

Very true! Now, there is a difference in brands, at least with my experience in the US.

So, run what the manufacturer states.... IE, when I had my S, it got premium, 'cause that's what the manual states.. In my 300, it gets 89 mid-grade...Again, what the manufacturer states....

A couple of side notes... Way back, GF ran premium in her new Chevy w/ 3.1 V6... EGR system failed with 20k on the car. Cause: running premium in a car engineered for regular (87).

Getting a hand held tuner for the Hemi. Many users in the LX body community. The unit has multiple tunes for various octanes. Basically maps the engine computer to prevent knock sensor intrusion. So, yea, the knock sensors will compensate for improper octane BUT doing so can result in unwanted deposits.. BTW, they are putting the finishing touches on an "economy" tune. Less HP, Better MPG (still to be proven), and mapped to 87 octane.. Hmmm..

 

If you use a fuel that's below the car maker's specified minimum octane, is it not entirely possible that the PCM won't back off the timing enough? (Due to being outside the programmed range.)

Anyone want to risk it? I don't!

 

Not totally related to the thread but interesting was back in the early 90's when fuel marketers were pushing the "premium" fuel on consumers it was causing problems. A lot of people were using high octane fuel in vehicles that did not require it leading to hard starting in cold weather conditions. Several manufacturers released bulletins stating on vehicles that were having cold start up problems in cold weather to make sure they were using lower octane fuels.

 

That gets us into the area of second guessing what Jaguar designed into the software. I've never heard of a car with such a fundamental blunder being made, but neither of us know for sure. Since a timing reduction of only 5-6 degrees would be required to resolve detonations issues, I'd be surprised if the engineering people 'forgot'.

On the other hand, field data indicates that S-types being run on 87 octane, whether done in ignorance or by design, have suffered no damage.

More to the point, I bought the car for it's performance potential and use 91 octane for that sole reason.

 

Is there much (any) such field data? News to me.
(I'm only interested, and not very LOL)

Looks to me like the answer to the thread is "premium: no; but at least the recommended (USA 91) octane: yes". (Or 87 if you don't care about any potential consequences.)

Here's an idea: if someone's going to use 87, why not also do oil changes every 20K miles? Saves another chunk of money and will it really matter.......

 

ok guys, lets not get too far off topic, or rehash old debates that often get out of control...hang on, flashback.

I think short term, it won't do any damage, maybe not much of a fuel mileage decrease. But long term, not only will it get even worse fuel mileage, you won't get any performance when you need it (all of a sudden it knocks? piece of junk...you'll be thinking) then it'll cost you 10x that amount you saved over the last couple years on 'lower octane' fuel (or buy the quick trip / race track gas) in that fuel injection cleanings, fuel filter changes (a possibility), more rapid plug fouling, maybe need a seafoam treatment...I'm with the majority here, buy the recommended grade of gas and use the name brand fuels with additives and detergents, unless of course, I have no option to do the same.

 

I find it all a little ironic.

Our owners' manuals are chock full of factory recommendations and admonishments on everything for what kind of fuel to use to required service intervals to leather conditioner.

Meanwhile the forums are chock full of discussions about our non-factory-spec alternatives on tires, oils, coolants, filters, leather conditioners, service intervals etc etc PLUS our modfications for more power, tighter suspension, brighter headlights, LED interior lights, exhaust changes, big-bigger-biggest wheels, poly bushings, and on and on. In other words, factory recommendations/specifications are *routinely* tossed out the window.

Somehow, though, when it comes to gasoline, varying from factory recommendation...even by those who have given the matter some thought and who are aware of and have weighed the pros and cons....creates a big buzz and gasps of disbelief! :-) :-)


Cheers
DD

 

Yup same here. The car might run on kerosene for all I know, but I'll never know since I only pump 91.

 

C'mon guys- can we get over the myth that low octane gas has insufficient cleaning additives?

Please?

 

Can't speak for others, but I'm not going to use anything with a LOWER spec than the maker says. I'm not gonna use crappy tires or ones with lower speed etc spec, wrong coolant, cheap filters etc. Similarly, I'm not gonna put in LOWER spec fuel and chance it being OK. (I don't put in higher, either, as it's just a waste of money.)

 

No problem with that.

Cleaning additives is a completely separate matter from octane boost and are directed at separate functional characteristics.

 

wow this has gotten out of control. Thank you for sharing your opinions but please if you don't have factual info to back yourself up just stop with the ultimatums. now i would like to say that when it comes to fluids i use only royal purple due to their proven results. a month or two back i decided to just try the cheapest fuel in my car and it ran fine but there was a decrease in power and gas millage. then i went back to premium for a week. after that i tried mid grade and there was literally no noticeable difference in power. since then i have been running premium because i still haven't heard a solid answer on if mid grade is going to cause a problem with the injectors or plugs. I have to admit i skipped over a page of responses because i havent been on in awhile and wanted to just say something after reading sooo many negative responses. i know what the manufacture says but a jaguar mech also told me a new fuel pump installed would be a few thousand....

 

In the coldest days of winter, I'll go with some mid grade for a while, but never the regular grade. When the weather gets upwards of mid 80's and higher, I stick with 91. Sometimes in cool weather, I'll go with half n' half, mid and premium, just to save a buck or two.

 

What's that got to do with anything?

Oh- you didn't bother reading a page or so of replies. Never mind.