I have have been feeding my XKR premium 93 ever since getting it (there's no 91 around here that I know of), but I noticed the other day that my local Sheetz sells 90 without ethanol.
Now I'm debating what's better for it long term, a slightly lower octane than the 91 specified by Jaguar but ethanol-free, or an excess rating (93) with up to 10% ethanol?
Searching the various threads discussing ethanol and octane didn't convince me either way, other than maybe with respect to winter storage (add stabilizer regardless of grade).
Anybody have thoughts on the subject?

Oh, and cost is not a factor here, I just don't drive it enough to make a noticeable difference in my wallet.
Thanks!

 

I live in an oil company town (Phillips Petroleum / Phillips 66) so all grades of gasoline are available without ethanol. The premium all-gas here is 91 octane. I’ve been using it for several decades in all types of vintage cars and motorcycles, and 7 years in my 2002 XKR. There’s no downside to it that I can tell. Going down to a 90 octane should not be an issue at all.

I wouldn’t bother with octane boosters . Nothing but a rip off. Those that advertise as raising your octane by 5 points are not saying it will go from a 90 to a 95. A “point” to them is 0.1 octane. So 5 “points is going from a 90 to a 90.5 !

that said, nothing wrong with using a 10% ethanol mix. Your gas mileage will decrease, but as long as you go thru a tank of gas in 4-5 months there’s absolutely no problem using it .

Z

 

The Engine Control Module can adapt for lower-octane fuel by retarding ignition timing. This has the adverse consequence of reducing both performance and fuel economy, but perhaps no more than using 10% ethanol fuel.

Considering the well-known problems with ethanol (lower energy density, hygroscopy, phase separation, corrosiveness, etc.), you might actually come out ahead using 90 octane ethanol-free fuel. If I could get it in our area I would definitely give it a try.

Cheers,

Don

 

Thanks guys!
I'm going to give the 90 a go.

 

Winter storage will be better with the ethanol free fuel. Ethanol is for race cars and should be used on the streets but the govmnt thinks (wrong) differently. Of course YMMV, TM

 

I assume the ethanol additive is to do with cost and/or meeting some targets somewhere in the headlong scramble to electrify everything.

Pretty sure there's no benefit to the motorist.

 

In the driving I’ve done thru states that produce a lot of corn, are you listening IOWA ?, it’s really difficult to buy pure gasoline anywhere, exactly the opposite of my oil company town where you can find ethanol only in 87 octane, but 3 grades of pure gas, no problem.

Another seldom mentioned aspect of the ethanol mandates, is that they negatively impact lower income people who depend on inexpensive corn based food products like tortillas for subsistence. A raw deal all the way around, but worse for them.

Z

 

With the driving season all but over, I wanted to follow up this thread.
Last year, I filled up with 90-octane ethanol-free before putting into storage as discussed, with some Stabil added. It may be my imagination, but it seemed like after I had run the tank down in the spring and refilled with 93 octane (10% ethanol), the engine responded better to throttle input, which suggests that 93 with 10% ethanol beats 90 ethanol-free for performance. Perhaps not very surprising.
This year, I debated mixing in 105-octane race fuel (lead-free!) with the 90 to get at least 91, but decided to instead try a compromise with roughly 11 gallons of 90 and 7 of 93, which should leave me with the recommended min of 91, with less than 4% ethanol. It will be interesting to see if I notice any performance-difference this time.
Yes, I'm probably overthinking this.

 

Given that the cars when new were designed to work on fuel with up to 10% ethanol (or up to 15% MTBE) it really shouldn't make any difference using 100% gasoline or not, so it's interesting to see that confirmed with your own experience. Of course 20+ years down the road, the car's air/fuel system isn't exactly how it left the factory, and a car that is already running heavily lean might well get tipped over the edge by ethanol in the fuel.

I run my car on supermarket 95 RON (= 91 AKI in the US) with 5% or 10% ethanol with no ill effects, as recommended in the Driver's Manual. Some people like to spend more on the "premium" 98 RON fuel, but it's difficult to see what difference that can make to a (low compression) engine not designed to use the higher octane, other than the placebo effect of buying the "premium" product. BTW "premium" octane in the US is not the same as "premium" in Europe, just to add to the confusion.

 

I have experimented on Premium 98 octane versus Regular 95 octane. When I used to commute 5 days a week using my BMW Z3 I was able to calculate that my running costs were actually lower overall when using the more expensive 98 octane, as I got better MPG, which mitigated the higher purchase price.

 

Not to distract from an interesting thread...

We have only about 1000 miles on our XK8 and have been using Sinclair 91 octane ethanol free gas almost exclusively. The only downside that we know of is the $1 more per gallon but at the rate we put on miles this is a small issue.

I have found that a post drive infusion of 40% Scottish sourced ethanol just makes the drive so much better!

 

On a supercharged car I would use 93 Octane, or the highest I could find closest to that if 93 was not available.

 

I agree. However in my region 91 pure gas is the best I can find. The next cross country trip I take I’ll be looking for a tankful of 93, just for comparison.

So far, the 91 is still giving the XKR enough acceleration to flatten my eyeballs.

Z