Possibly the absence of data either in the horrors of low octane or the wonders of extra-high octane suggests that there's not much to tell.

Given the tendency for people to jump in with posts after making even the most minors mods claiming that they gained something, or the other half who moan about the tiniest problem, I'd think by now someone would have seen something at least once.

 

The fact is, there ar emany failure modes reported, including some that are questioned as to validity by the group. (Chain tensioners, rear axles, oil level related engine fails). I have yet to see a "hole in piston" or a broken ring on a modern jag engine. Did I miss one?
That is significant in that I assure you there are many foks out there putting regular gas in their Jag-u-wah. Not that I do! It is because I do not want the ECU dialing back the timing and killing the performance, not that I am afraid of grenading the combustion chambers.

 

I'm jumping in here not to support one side of the argument or the other but to dispel the ardent belief that 87 AKI fuel is not acceptable. It clearly is, as stated by Jaguar.

If there was even a possibility of it causing damage to the car, Jaguar would not release it. Rather they steer you to use 91 AKI for optimal performance and MPG.

I hope to take away fear from people from using whatever they feel like using between 87 - 93 AKI. It's okay

 

Nobody has yet explained why they would want to run 87 in their car. Is it really just to save $3 per fillup?

 

Apparently so, for most of those who do.

 

JagV8...

Just wondering, are you folks in the UK stuck with just/only 10% Ethanoil mixed petrol, or is it 100%?...Here in the US, some areas of the country E10 is all you can get...Fortunately I can get 100% gasoline here in Oklahoma.

 

Why buy the car if you cannot afford the fuel? For show? To appear that you have made it. Your car, your bill. You will find after a while your fuel economy will suffer along with the engine performance. If you don't drive the car occasionally for spirit, the car will slow down, as the computer learns your driving. The next person will be lost on the car as it would have to be programmed for the new driver. I get the premium question all the time from MINI, Land Rover, Audi, and Mercedes owners. It is a shame that fuel getting cheaper has drivers squeaking at the expense of fine automobiles.

 

It might be $3 per fill up for some, but that's not the case everywhere.

The difference in price from grade to grade varies considerably from one place to another. Here, it's usually $0.15 per litre difference or just under $10 per tank. For someone using 2-3 tanks per week, that adds up.

What's infuriating here and I suppose in many places, is during gas price wars where only the low octane fuel that is discounted. The intermediate and high octane grades remain at their non-discounted price. The difference in price per tank can then be $15.

Another physiological effect, occurring here presently, is regular fuel is routinely under $1.00/L while premium is always over. Human nature says that something at .99 is far cheaper than $1.00.

It's easy to mock such logic or scorn those that contemplate saving a few bucks, but when it comes out that it cannot even be shown to be a false economy, never mind the sky-is-falling crowd's dire predictions, who really has the last laugh?

I'd bet that 99% of drivers don't have a clue as to what high octane gas is and why it might be required. I think it's fair question and don't blame the OP for asking.

 

Just as a frame of reference for this discussion-
The price for No Ethanol Gas here in Atlanta GA is $3.99 per gallon if you can find it.
The price for regular E-10 is $ 1.89 or so.

I figured we would get to the Ethanol conspiracy theory eventually!

 

And it's frequently those who openly ridicule the low octane concept and call them 'cheap' who buy the ethanol free at a substantial surcharge.

Nowt so queer as folk.

 

seems like the 4.2L was dumbed down or something.

For a 4.0L in the X308

Fuel Requirements
Use only Premium Unleaded gasoline with a minimum
Anti-Knock Index (AKI) of 91.
Oxygenated gasoline blended with ethanol (max. 10%)
methanol (max 10%) or
methyl tertiary butyl ether (MTBE) (max. 15%) may be
used.
Reformulated Gasoline with a minimum AKI of 91 may
also be used

91 AKI minimum ... full stop.

Now, it seems that the 4.2L has a recommended octane and a non-recommended option.

It seems hypocritical that a certain contingent takes two opposite tacks on oil and fuel.

On oil, they stamp their feet, hold their breath, and otherwise engage in tantrums over oil
insisting that the recommended option is the only proper option without giving due regard
to the acceptable options.

On fuel, they throw the same fits insisting that the alternative option is the way to go
despite a clearly stated recommended option.

Even though the alternative option comes with the stipulation that it comes at the
cost of:

but performance and fuel economy will be reduced.

Furthermore, on oil they insist that only Jaguar engineers know best. But, on fuel
they rely on anecdote and speculation while ignoring a Jaguar engineering statement.



++

 

Plums:
I doubt you are referring to anything I have said concerning oil- BUT there is a difference. On oil, the issue is not so much whether one brand and grade of oil is better than another, but rather that one is explicitly and expressly stated as a requirement for continued warranty.

I was given a document with my warranty paperwork that clearly warned me that use of any oil except that which specified would void the warranty for engine internal components. I am not arguing or debating the legality of that statement by Jaguar, but I am disinclined to test them in court on the matter, so I will attempt to find and use the specified oil after the oil changes they provide as part of the new car warranty.

I do not believe there is any explicit threat to deny warranty for gasoline as long as it meets the AKI 87 specification and is not greater than 10% ethanol.

 

Plums - I can well believe it as it's a simpler PCM in the pre-2003 cars with less CPU power etc.

 

I don't even look. The cars can cope with some ethanol and petrol is sold by RON-rating here. I just buy same as jag spec (95RON) and car's been happy for 55K miles, near 7 years so far.

I worry far far more about our wet, cool, salty roads and the rust monster.

95RON (roughly 91AKI) fuel is now "cheap" (for here) - about $1.55/l i.e. $5.90 per US gal.

It's fairly easy to buy higher octane (I don't) but I don't know offhand anywhere with lower (I wouldn't buy it anyway).

 

Good points and I believe that it was not you being addressed in the post above. In addition to what you've mentioned, there's obvious differences between 'experimenting' with alternate fuels and oils.

1) factory recommendations

In the case of fuels, Jag has already covered it in the owners manual. Essentially, if 87AKI is used, reduced performance and increased fuel consumption can be expected. There is further mention of light detonation and it's acceptability.

Far from being non-recommended as inferred above, this is a factory endorsement of it's use, not that far different from the mention of E10 (and now E15 on the latest models) Each is specifically accepted and contains a caveat of what might be expected with it's use.

For oil- one viscosity is 'recommended' and a simple chart showing the suitability of alternates is provided. No mention is made of oil types or viscosities outside this range is provided.

Nowhere have you (or I) recommended anything outside what is already provided for in the owner's manual.

2) owner inspired experimentation

Some like to do this. I do. I brew beer as a hobby. If I monkey around with a tried and true recipe, the worst that can happen is it's not pleasant and I've wasted $10-15 on ingredients and energy. On the other hand, I might just have hit on something good. A very reasonable risk to take.

For cars-

Fuel. Jag has already stated that 87AKI and up is OK, and we know that there's nothing to gain by using higher levels than optimum, so let's say that extra-low 85AKI was available here (~150 meters above seal level).

What's at risk with it's use? Detonation, even lower performance and worse fuel consumption. Each of which would be IMMEDIATELY apparent. The experiment could be discontinued by substituting higher octane fuel, with no harm done to the engine.

What would be gained by experimenting in the first place? Maybe saving a few dollars per tankful.

Oil. Jag has stated a range of viscosities that are acceptable. There are however oils on the market that fall outside this range.

What's at risk? Accelerated engine wear or complete failure. Replacement cost is well over $10K on some models. The main issue is that unlike non-standard fuels, accelerated wear caused by non-standard oils may not be immediately apparent and is not reversible by the discontinuation of the experiment.

What can be gained? It is known that the engines live long and happy lives on the factory recommended viscosities and types of oils. The few reported failures have little or nothing to do with oil related deficiencies. Alternate oils frequently are difficult to find and carry a higher price tag.

No gains as far as I can see and too big a risk in the first place.

Schizophrenia indeed.

 

I live just outside Chicago, there are no 91 options, it's 87,89,93. I have always used 93 octane, but presently 87 is around $1.95 and 93 is $2.89. In addition to my 2011 XF I also own a 2016 Acura MDX that is also direct injection. I can certainly "afford" 93 octane, but if i were to know for a fact that 87 octane would have no measurable negative impact on either car, I wouldn't mind saving $35 a week between my wife and I in gas.

 

I wish we had 93 octane around me...My Jag would run with it's intended performance by design..

All I will say to your concerns is that it's simple..The car was DESIGNED to run on 91 octane or better...Anything less than 91 octane would be doing the car a big disservice...Might as well own a KIA and then you'd have a car designed for 87 octane..Just saying..You own a Jag, treat it like a JAG..

 

Jaguar's position on low octane fuel has been discussed at length. What does your Acura owner's manual say?

 

Ninety Three For Me and That's my story and I'm sticking to it.

 

Yep, that's what this argument comes down to!