Can I moderate the two sides (91 Believers and 87 Believers) of this discussion?

For the 87 Believers, continue to use 87 based on the small mention in the manual. No empirical data exists that it's the wrong thing to do. Save your money and don't complain if you have any piston related issues (not saying you will).

For the 91 Believers, stop worrying about what others are doing. If the 87 Believers want to go against convention, who cares. Won't cost you a penny should they be wrong (again, not saying it will) and they should have some extra bucks to pay for repairs.

Can we please stop talking about this until some detonation catastrophe occurs in a vehicle running on 87 octane? Otherwise it's like two lifelong blind men arguing about the color of the sky...no winner can be named because at this point it's subjective.

 

I see where you're going and don't disagree- but the issue is not the 'possibility of detonation catastrophes' or 'piston related' issues. That is a red herring thrown in by those not familiar with how modern engine controls operate or had not bothered reading the owner's manual which is quite clear on the subject.

Let's just drop such scare-mongering garbage once and for all.

The issue is strictly whether performance and fuel mileage is affected, as cautioned by the OEM, and to what degree. We've got multiple posters with direct first person experience who say 'no' and not one person who has said yes. That's not subjective in the least.

 

Mikey, the reason I mentioned the piston issues is that's the only real question as to whether you should or shouldn't. Loss of a few hp and mileage, should that occur with 87, and not saying it does because I don't know that either, isn't a big deal.

Detonation damage to a piston would be a big deal. So if there's no evidence that it's happening in the 4.2 or 5.0 engines running 87, then owners should do what they want until/if such an occurrence happens. Then we can start this up again

 

Keep in mind that there's little or no evidence of any modern computer controlled engine, Jag or otherwise, that has suffered damage from low octane fuel. I would think that the 20+ years that such engines have been in common usage would have provided sufficient opportunity for evidence to appear.

The question did not first surface with the advent of the XF model, nor with it's predecessor the S-type in 1999. It's since been asked and re-asked to point of absurdity. OEM's have gradually refined and clarified their instructions in the owner's manuals attempting to educate, seemingly to no avail.

There again, unleaded fuels have been the only option for 40ish years and there are still those that argue that they damage engines and pine for the good old days....

 

The quality of gas has also changed with ethanol and winter blends, especially in CA where I'm at.

 

In other words, "Who has information, even anecdotally, about a modern Jaguar engine with a hole in it's piston, whether or not it was blamed on low octane gas?" Since it is clear that at least more than a few folks run low octane fuel, why are there no catastrophes reported?

That said, I understand Kyanite's position completely, and I almost always run 95 myself, allowing me to feel good about myself and my car!

 

Of course the 87 beliebers are also usually ethanol apologists.

Pulled ignition timing means nothing to them, failed fuel pumps have
no connection to ethanol, pinholed fuel rails mean nothing to them,
NHTSA recalls involving tens of thousands of vehicles due to ethanol
corrosion are to be studiously ignored, repeatable odb-ii mileage logging
is merely anecdotal and of no consequence.

 

Yes, that's another popular myth.

Today's gasoline is light years ahead of what we had 10-15 years ago. CA gas is no better/worse than anywhere else.

 

Except that other places can get 93 octane and choose pure gasoline

 

So much for your attempts to 'moderate'.

 

I was moderating the 87 vs 91 debate. I still stand by my statement that people should do what they think is right and not lecture others for their beliefs as there is no evidence anything bad will happen.

Now...I did make a quality of gas in CA comment, and you made a statement I didn't agree with. So I responded with two examples of what I meant in my original comment.

Two completely separate topics.

 

I prefer to use what Jaguar clearly intend as they're likely far better engineers with their engines than I am. Everyone should make their own choice for their own reasons.

 

Heh heh, when people stop reflexively blaming E10 for every fuel-related issue, and balance criticisms with an acknowledgment that the majority of motorists using E10 suffer no damage or problems whatsoever, you'll probably see a corresponding drop in commentary from 'apologists'

As one of the 'apologists' I've always agreed that E10 can be a problem under certain circumstances. Oddly, though, I don't believe I've ever heard the reciprocal from the anti-E10 crowd. IOW, when someone reflexively blames E10 for a problem when there is clearly no basis for doing so, or the basis has not yet been established, I've never heard the anti-E10 crowd jump in and say "Well, hold on just a minute here. It might have nothing to do with E10." No, they're perfectly willing to let unfounded E10 criticism slip by, unchecked. In other words, the more people who 'pile on' with anti-E10 remarks, a bigger and better "Anti-E10 fest" can be enjoyed.

When the same people then turn around and claim that non-E10 fuel turned their purring pussycat into a roaring tiger, and they're getting 20% better fuel economy, and the paint looks glossier, and their wife has changed from a unforgiving nag to a sultry seductress, anxious to please...well...it becomes a bit less believable

That's how it often looks to me, at least.


Cheers
DD

 

OK. I'll switch hats too.

If it makes you (or anybody else here) happy, I have ready access to 94 AKI 'pure' gas . The particular brand uses Techron additive and is Top Tier rated. Ne plus ultra!

It's a little bit of a drive to get there and the fuel (last time I checked) is the equivalent of about .30 cents US a gallon more expensive but if it made any tangible positive difference, I'd use it.

It doesn't, so I don't.

My winter beater and summer boat hauler Lincoln SUV has the Ford 4.6L 32V DOHC engine found more commonly in the Mustang. With 11:1 compression it comes not surprisingly with a recommendation to use 'premium fuel'.

It came to me almost three years ago in well used but never abused condition with just under 200K KM on it. As related elsewhere I discovered that the previous owner had consistently used 87AKI fuel almost since the vehicle was new. His explanation was that 'premium' meant Top Tier brands instead of so called 'off brands' and nothing to do with octane. His statement was that if Lincoln meant 91 AKI fuel they should have put that on the fuel flap sticker. I can't wonder how many other motorists have done something similar.

Having said all that, I did notice that the engine had a slight miss at idle when in gear. Fearing that all the hype over octane and additives with regular vs. premium fuel might be true, I started using the all-hailed Techron-laced 94 AKI pure gas.

No change.

Fearing now that the damage was permanent, I started doing some light investigation, thinking that possibly one or more cylinders might have low compression. Removing the engine cover revealed a vacuum leak from a perished rubber elbow in the EGR line. A $10 fix and the engine idles as smooth as silk.

Since our Jags don't seem to challenge the engine sufficiently to induce detonation and resulting ignition retard, I've toyed with the idea of towing my 2 ton boat and trailer behind the SUV while using 87 octane. I would think that the all-up weight of just under 9000 pounds should be sufficient load.

 

Following is a list of gasoline additives according to WIKI (so you KNOW it must be true!)
So, even if terrible things are happening to fuel systems on modern cars, (which just ain't happening!) how can you blame ethanol alone for these problems? Oh yeah, I remember. My brother in law has pumped gas and raced cars for 50 years and he said it!

Oxygenates
Alcohols:
Methanol (MeOH)
Ethanol (EtOH)
Isopropyl alcohol (IPA)
n-butanol (BuOH)
Gasoline grade t-butanol (GTBA)
Ethers:
Methyl tert-butyl ether (MTBE), now outlawed in many states of the U.S. for road use, mostly because of water contamination.
Tertiary amyl methyl ether (TAME)
Tertiary hexyl methyl ether (THEME)
Ethyl tertiary butyl ether (ETBE)
Tertiary amyl ethyl ether (TAEE)
Diisopropyl ether (DIPE)

Antioxidants, stabilizers
Butylated hydroxytoluene (BHT)
2,4-Dimethyl-6-tert-butylphenol
2,6-Di-tert-butylphenol (2,6-DTBP)
p-Phenylenediamine
Ethylenediamine

Antiknock agents
Tetraethyllead, now banned almost everywhere for causing brain damage.
Methylcyclopentadienyl manganese tricarbonyl (MMT) is a extremely poisonous neurotoxic substance and is fatal if swallowed/inhaled and will cause a disease similar to Parkinson's called manganism.[1]
Ferrocene highly toxic[2]
Toluene
Isooctane
Triptane

Lead scavengers (for leaded gasoline)
Tricresyl phosphate (TCP) (also an AW additive and EP additive)
1,2-Dibromoethane
1,2-Dichloroethane

Fuel dyes, most common:
Solvent Red 24
Solvent Red 26
Solvent Yellow 124
Solvent Blue 35

Fuel additives in general
Ether and other flammable hydrocarbons have been used extensively as starting fluid for many difficult-to-start engines, especially diesel engines
Nitromethane, or "nitro," is a high-performance racing fuel
Acetone is a vaporization additive, mainly used with methanol racing fuel to improve vaporisation at start up
Butyl rubber (as polyisobutylene succinimide, detergent to prevent fouling of diesel fuel injectors)
Picrate improves combustion, increases fuel mileage