Kevin D, I don't think anyone in this thread was trying to say that you shouldn't be free to choose whichever brand of gas you want to use. The OP just asked which brand of gas people preferred, and the other members chimed in with their understanding on the subject.

Personally, I buy gas from whichever gas station is most convenient. I'm not going to fight traffic at a busy intersection to save 34 cents on a fill up, nor will I fight that traffic in order to buy a name brand. I look for the gas station that's easy to get to and allows me to pay at the pump. If you want to go out of your way to buy a specific brand, then you have every right to do so. I was merely saying that I don't see the need for that.

 

That's all I was saying too. No intent to offend anyone- just putting some science and fact behind the smoke and mirrors of the petroleum industry.

 

I don't go out of my way a bit Sam.

The fact is that the Winn Dixie grocery store where I shop and get my prescriptions is next door to a Shell Station, and my Winn Dixie card offers me a discount on 20 gallons of Shell Gasoline a month. I typically get about 80 cents off per gallon and, along with the 3% that I get by using my Business Chase credit card it's a decent savings.

The OP was asking about "the best gas", not the most convenient gas or the cheapest gas, so, clearly he was looking for the "best gas", so perhaps he IS looking to go out of his way, and my response was to his OP.

It went sideways with all gas being exactly the same, which is basically true for the raw gas, but as noted, each supplier adds the additives that most of the people in the petrochemical industry (you know, the ones with master's degrees and years of practical experience) believe are beneficial to the engine, over just the raw gas, so that for someone who specifically was looking for "the best gas" the additives are a consideration.

Now, apparently some people believe that the additives are all "smoke and mirrors" and are determined to post until the end of time to assert that supposition. Personally, I don't think that the engineers and decision makers for the major brands add expense to their product by putting in an excessive amount of additives as some have implied.

My own particular background is that my father worked at and retired from a Shell Oil refinery after 35 years and related many things to me over the years regarding gasoline, and one of those things was that he said that he would like me to buy Shell Gasoline if I could because Shell Oil had provided very well for our family over the years, but, that if I did buy some other gasoline that I should buy one of the major brands because he said that that gasoline was better for your car than the gasoline from the cheapest places you could buy it. I believe that he was right, and I believe that a person who is looking for "the best gas" would be wise to purchase one of the major brands, but I won't ridicule him or call him a conspiracy nut or deride him by saying that he "is drinking the kool aid" or some other sort of name, no matter which brand of gas he chooses to buy.

I think that the forum member of the OP was given quite a bit of information regarding his choice of gasoline, and I hope he acts accordingly.

 

Most of the discussion has been about brand and additives.

I have a 2005 XK8 Convertible - approx. 60,000 miles, and I have always used the extra (not super) grade of gasoline - 89 to 91 octane - I think we may assume that the octane rating is correct.

I do most of my driving fairly close to sea level, and I don't really push it as a performance car. I have had no problem with using the extra grade.

I have occasionally used super when driving in the eastern U.S. mountains, and have not detected any difference. My regular mechanic who specializes in Jaguars doesn't see any problem.

What grade of gas do some of you use?

 

The 2006 XK8 is my wife's car so she usually fills the tank. She believes the 4.2 V8 runs smoother with 93. I put 91 in the tank when I fill it up, and there have been times when I've even bought a tank of 89. I perceive no difference at all. But because I'm far too tall to comfortably fit in the XK8, I rarely drive it....

Our 2005 S-Type 3.0 always gets 87 or 89 and runs just as well today at not quite 71,000 miles as it did when we purchased it at 18,000 miles....

 

Now the topic is going away from 'which is best' to 'which octane rating do people use'. Being that the question of 'best' is impossible to answer as no one can apparently come forward and show that any given brand is any worse than another- it seems then there's no 'bad' gas out there other than anecdotal stories and myths.

On the topic of octane, and understanding that the octane parameter or rating measures only the resistance to detonation and absolutely nothing else including the amount of additivies or the 'quality' or the amount energy it contains, I believe that most or all of the Jaguars commonly discussed here state a recommended minimum octane rating of 95 RON in the owners manual. The RON rating system has not been used in North America since the mid 1970s, when we adopted the AKI system 95 RON gasoline is approximately equivalent to 90-91 AKI.

There is NO benefit whatsoever in using gas with a higher octane rating than this- despite the common myths that engine start easier, run smoother, more powerful, etc, etc., it's just money wasted.

Using fuel with a LOWER octane rating will also have no effect whatsoever-unless the engine is pushed into a condition where detonation (pinging/knocking) is encountered. This is typically full throttle, high RPM acceleration, or use of too low of a gear while climbing a hill- 'lugging the engine'. Pre-computerised cars had no mechanism of retarding the ignition timing to quell the detonation and it was up the driver to lift off the throttle or select a more appropriate gear.

Modern cars like our Jags have knock sensors built into the engines and automatically retard the timing while detonation is still below the audible threshold- most time we are oblivious to this process occuring.

The only drawback of this action is a temporary loss of horsepower and increased fuel consumption- but only for the very brief period that the knock sensors are 'doing their thing'. Non-sporting drivers may have never pushed the car hard enough to cause the engine to come close to the detonation threshold, so for them, the extra money they've paid for the recommended 91 octane gas was wasted. I drive my S-type on 87 whenever I'm heading out on a long highway trip. Constant speed on flat land is about the furthest removed conditions that one can find for inducing detonation.

Hopefully the above helps explain more of the mysteries behind gasoline.

 

Whoa, now there's a lot of misinformation. I'll write more when my Friday evening has worn off. ;-)

 

Well Beav, you deal with him. I am done.

 

I always heard that if you buy premium, no matter what brand, it includes what you would buy if you got one of those bottles of injection cleaners and other engine cleaners. I don't know if it's true but I'm positive that there are differences between the grades of gas and I believe it adds up over time, but I really don't think it makes a difference what brand but I'd stick with any of the major ones, since they're usually everywhere anyways it's not an issue.

 

I'm always willing to listen and learn.

You really need to get that chip off your shoulder dude...............

 

No Mikey, YOU need to get the chip off of yours. You are clearly a guy who MUST have the last word and will go to the end of the Earth to have it.

I have tried to diplomatically end this with you about three times and you will simply NOT let it go.

You have some long standing agenda that you are determined to drive to the end.

This will be my last post in this thread, and your undoubted reply and continued replies will only prove my point.

You joined this forum several months after I did and you have 2,255 posts and I have 333. Yeah, I get it, you are a prolific poster, to say the least.

ONCE AGAIN, Mikey, go on and live happily ever after!!!

Yeah, I know, you simply CANNOT let it go, I get it. Bye now.

 

...and this is why oil and gasoline topics get shut down way before a thread can run its course. Once you see a few of these like I have, you just start avoiding them (unless you see a post count of 50 in it, then it gets clicked on.

I can't lock it down myself anymore, but how about just letting a few personal tangents fade out. I would like to hear what Beav has to add.

 

Matt What are you doing up at 4 AM ? Go back to bed.

 

That's the most valid reason to pick one brand of gas over another that I've seen in this thread so far.

 

After I installed the supercharger pulley I would get the occasional lean code.

Not anymore after I started using Chevron 94.

 

"Using fuel with a LOWER octane rating will also have no effect whatsoever-unless the engine is pushed into a condition where detonation (pinging/knocking) is encountered. This is typically full throttle, high RPM acceleration, or use of too low of a gear while climbing a hill- 'lugging the engine'."

Mostly wrong. Using fuel with a lower octane reading will have no effect until detonation occurs. However, it is not typically at full throttle. RON & MON test engines specifically operate at 600-900 rpm. Audible detonation is normally noticed in the 1100-1800 rpm range, though it actually begins at much lower engine speeds. Just because you don't hear it doesn't mean it isn't happening (the 'ignorance is bliss until the **** hits the fan' factor.) 'Lugging an engine' refers to selecting too high a gear in relation to engine speed and load.


"Modern cars like our Jags have knock sensors built into the engines and automatically retard the timing while detonation is still below the audible threshold- most time we are oblivious to this process occurring."

Correct - to a point. They do detect mostly inaudible detonation and the ECU can alter the timing map in order to reduce the problem. But there are always caveats. The ECU can only retard the timing so far. Then what? You may think, "I can't hear it happening so I'm smarter than the peeps that designed the engine!" and/or some wild conspiracy theory may come to mind. What if the ECU could only reduce the detonation to the inaudible level? What if your EGR system is compromised? (In my experience I've found most peeps a) don't realize it helps reduce detonation b) is not used as a way to reintroduce unburnt hydrocarbons into the combustion process in order to complete their combustion c) do not know that the EGR is used to introduce an inert gas - low/no O2 content - in order to reduce combustion temperatures and reduce NOx emissions)

"The only drawback of this action is a temporary loss of horsepower and increased fuel consumption- but only for the very brief period that the knock sensors are 'doing their thing'. Non-sporting drivers may have never pushed the car hard enough to cause the engine to come close to the detonation threshold, so for them, the extra money they've paid for the recommended 91 octane gas was wasted. I drive my S-type on 87 whenever I'm heading out on a long highway trip. Constant speed on flat land is about the furthest removed conditions that one can find for inducing detonation."

You bring up what seems to be some good points but the fact remains the most common time for detonation to occur is at lower rpm during all but the lightest of touch on the throttle. That adds up to a lot of lost performance and possible economy for the average motorist. Yes, driving the Interstate through Kansas in the spring or fall would probably reflect little need for high octane. You have also neglected to consider the shift maps of computerized cars being tuned for improved mpg by shifting into higher gears as quickly as possible. When left in 'Normal' I often notice my car in a higher gear than I would have selected while doing nothing more than climbing a small hill on my way home from work.

Anyway, the title of this thread was, "Which gas is best?", not a question regarding octane numbers, etc. Along that line my recommendation to visit TopTier Gas was spot-on. And I agree whole-heartedly with Sam, I'm not going out of my way to save a buck or two on gas but I will avoid crummy gas.

And, yes, I do fill up with premium fuel. I figure if I had to worry about the extra few cents/gallon I should probably be riding public transportation.

 

I mispoke regarding the nomenclature of the transmission gear by thinking of 'low reduction ratio' ie direct drive or an overdrive, rather than the gear selector position, 4th, 5th gear etc, when 2nd or 3rd may be more appropriate. Point taken

Your other points regarding engine speed are also correct- but engine load, throttle position and ignition advance curves also play a major part of when detonation may occur when driving a car vs. test engine in a lab strictly used for determining octane ratings. High RPM detonation is frequently seen on high compression non-computerized engines that are otherwise 'immune' to low speed issues unless the engine is 'lugged' as mentioned above.

As to 'which gas is best'- that question is no more likely to be resolved than 'which beer is best'.

 

Budweiser! The original cold, golden Budweiser! Not any of that 'lite' crap!

Just picked a 30 pack for the 4th celebration.

The gas discussion had gotten old!

 

Regarding whether to use regular or premium fuel is an important discussion.

My 03 XK8 requires 91 AKI fuel, so what happens if I use 87 or 89 AKI gas? For the sake of discussion lets pick some numbers out of the air. For instance, 91 oct fuel can withstand 91 psi of combustion before detonating on its own, 87 can withstand 87, etc. Now lets suppose my engine develops 90 PSI of compression at TDC. If I have 87 oct. fuel in it, then, when the piston compresses the mixture to 87 psi, the fuel will detonate before reaching TDC thus causing pinging. Obviously then, if i'm using 91 oct fuel, the piston will reach TDC on the compression stroke wherein the spark plug will ignite it at the proper time.

What then, if I want to be good to my engine and use the best fuel available, say, 93 oct? Well, since my engine can't develop 93 psi, that other 2 points of octane rating (for which I paid 15 cents per gallon extra) is unused.

My engine can develop only the power designed into it. Using a higher grade fuel won't produce any more power. Using a lower grade fuel WILL cause detonation even if you can't hear it.

 

It was old years ago. Still the misinformation continues....