Good Day Experts!

1999 XJ8L
I live in New Orleans.

I tried using 3 tankfuls of non-ethanol gas in my 1999 XJ8L and I did notice it had a bit more get up and go! With this last tank, I noticed that on a cold start, the engine no longer immediately fires up. It whines for a few seconds before starting. It does however starts. If I go to the store about 3 miles away, it sometimes whines a bit when I start it up to come home. Other times, it fires right up. It's a new sound that I have not heard before. It may have nothing to do with the gas and it may be something else.

Should I be using non-ethanol and go back to premium? One thing I did notice is that before using the non-ethanol, my gas gauge was not working properly. When I switched to non-ethanol, the gas gauge suddenly started to work again. Another strange thing.

I have been so pleased with this vehicle not having any major problems. At 22 years old, I do expect to have some issues.

Any thoughts for all of you great advisors?

 

I am not a gasoline expert. But I can tell you I had to put new heads on an '89 XJ6 or a '97 XJ6L, in one instance because I burned a valve thinking I could get away with running mid-grade gas or mixing it with 93 octane. It was an extraordinarily expensive lesson. So, if there is an octane difference between the two fuels you reference, I'd stick with the 93- or better octane regardless of the ethanol issue. Costco sells Top Tier premium at about an 80-cent or better difference against regular gas stations in my area if you need good fuel at a reasonable price. The savings for running the wrong fuel will never cover burned valves. Now, if you're handy with a wrench and want to see the inside of your engine ....

Eliot

 

Thank you Eliot. I’ll stick with The high octane.

 

both of those cars are not mapped for premium gas. the 3.6 XJ40 is designed for 87 and the X300 maxes out at 90 octane, plus it has a very effective knock control system.

 

What octane would you suggest is best for the ‘99 XJ8?

 

Xalty/Crystal Wells: I STAND MOSTLY CORRECTED: The specifications page on my ‘03 VDP says the car should have “premium unleaded gasoline with an Anti-Knock Index (AKI) of 91.” Upon reading, I find the AKI is another way of expressing octane. Research also shows me that the roughly similar engine from the Lincoln LS of that era also says 91. (Xalty — I am dutifully falling on my sword!)

Now, the trick is finding 91. All mid-grade gas in my area (northern Virginia) appears to be 89 octane. It’s priced anywhere from 20- 40-cents less than 93 octane. Prices this morning at my local Shell top-tier (recommended) station were 2.80, 3.58 and 3.97 respectively. My Costco has only carries 87 octane for 2.69 and 93 octane for 2.89. So, in lieu of 91 octane my default is 93, and Costco is roughly $1 per gallon less for the slight overkill in similar octane rating ... and about 70 cents under Shell’s price for unusable midgrade 89 octane.

This is not a discussion of price, I just offer those numbers for comparison. If I could find top tier brand 91 octane I might try it, but I can’t. My default is 93 and buying at Costco keeps costs reasonable, i.e. roughly $20 less a tank for top tier fuel. (Crystal: if you are unfamiliar with top tier, here’s a link https://www.toptiergas.com/licensed-brands/ ... https://www.consumerreports.org/car-...h-extra-price/

Eliot

 

I was talking about the 4.0 6 cylinder where there is no benefit to using anything over 90. The V8 definitely benefits from 93.

 

Use the 93 octane whenever/wherever available in the X308s. I need to run by the local Costco and check price (80c USD) difference over mainline gas sources is significant enough to pay their silly dues, unless you are buying 100 rolls of Kirkland toilet paper.

California: have yet to see gas over 91 octane. But for my last Jag, years ago,I found this Exxon station in Lewisburg WV that had 93 ethanol free gas -- like rocket fuel! Not available in the People's Republic of Virginia. In North Carolina, I frequently find 89 octane non-ethanol -- my Lincoln prefers 93 10%ethanol.

 

Xalty:I clearly did not initially pick up on the differentiation between the 6 and 8 cylinder engines. My first cylinder head problem was in the 3.6 straight six in my '89, and then again in the 4.0 six in my '97. So, I stand further corrected and thank you for the education.

And JHartz: yes, the savings on just about three tanks of Costco 93 octane will cover the Costco dues, and the savings on hearing aid batteries, toilet paper, etc., are icing on the cake since you happen to be there anyway!. I know Lewisburg, but I don't think I'd drive there from Annandale just for non-ethanol 93. If memory serves me, ethanol is added in Virginia only for either summer or winter months (I forget which), or at least it used to be only a part-year thing.

So I, too, am sticking with 93.

 

In VA ethanol is a year round, all classes