In the August 2012 issue of Consumer Reports, there is an article on the "Myths at the Gas Pump". One of the myths it talks about is using premium gas. The article states the following:

"Our advice: If the owner's manual say that premium gas is "recommended" or uses similar wording, you can prbably use regular. If it says premium is required, play it safe with the right octane."

I have a 2012 XF Portfolio and my owners manual says "Premium unleaded gasoline with...octane rating of 91 or higher should be used."

Since the owners manual uses the term "should" and not "required", according to Consumer Reports, regular gas would be ok.

My questions to you all....Do you use premium or regular? Have you noticed a difference in performance or gas mileage if you use regular?

Thanks,

Ken

 

On the 95' XJ6 I use anything. from regular to premium depending on conditions. For around town where light loads are expected and ambient temps aren't high I'll use a reputable brand of regular. Around town in a hilly place like San Francisco I probably would use mid or high grade. On a highway trip through hills and mountains I'd use premium. During the hot summer months I lean towards higher octanes. On the way home to Virginia with our new California bought, 1997 XK8 I've only used premium. Interesting point is that on our way home the premium grade of gas was only 91 octane in the west. Places midway across the U.S., the best octane rating dropped to 90. Closer to the East coast the octane ratings improved to 93 octane. I was told it was due to emissions. Perhaps someone can explain that to me.

 

Gents, not trying to snub or be offensive, but enter the word "octane" in the search box above and scroll thru the pages. You'll find numerous threads....sometimes 60-70-80 postings each....on this very topic.

Some of our more loquacious members might chime in here but I doubt that anything new will be added to the debate. It's all been said, ad nauseam :-)

Cheers
DD

 

Did somebody call me?

Use premium fuel in the XF. The engine is designed for European regular gas which is 95 RON. Our premium is the same rated at 91 PON.

Although modern engines can usually run on lower octane fuel without damage the power output is compromised. Peak torque will suffer. You may get improved fuel economy on the highway.

Speed has nothing to do with octane requirements. Knock results from bmep exceeding the capability of the fuel to resist knock in a particular engine. Bmep peaks at peak torque output, not at peak power output. Accordingly, you can get away with using lower octane fuel at higher elevations ( non supercharged), warmer weather and smaller throttle openings. Fuel availability with higher octane is governed by these factors in your local market. The highest octane generally available in high elevation markets is 91. While you may be able to buy 94 it won't be worth it if you drive at 3,000 ft elevation, for example.

 

Nothing but Premum (93). The NA 5 liter in the Jaguar line up has high compression of 11.5. Putting regular will only cause detonation and have the knock sensor take the HP away and may damage some things on the way.

All of this just to save less than $500 a year. I always say, if one can't afford the type of gas the car needs, he/she is driving the wrong car.

 

Sorry Doug. I did a seach of "premium gas" and looked throught the first 15 pages of results and didn't see anything current or relevant, especially to the XF.

I will seach through "octane".

Thanks.

 

I take consumer reports "reports" with a grain of salt.

 

Don't confine yourself to the XF section, there's plenty to read about the merits of the various grades of gas in every section.

 

The use of a lower octane fuel in an engine designed to run on a higher octane fuel will reduce power output and fuel efficiency in said engine resulting in reduced mileage and increased fuel consumption. However, using a higer octane fuel than an engine requires won't produce aditional HP nor improve gas mileage. So the moral to the story is to follow your automobile manufacturers recommendation when it comes to fuel octane or RON rating or suffer the consequences.

 

and a non-loquacious '+1' to that!

 

To my understanding of the English language, "should" is more like "required" than "recommended". It's a binary thing: either you should, or you shouldn't.

 

Should derives from shall which is first cousin to must.

Modern engines are often able to protect themselves from detonation by retarding the ignition responding to inputs from a knock sensor. Modern direct ignition systems are capable of detecting knock by sensing the ionization of combustion gas across the park plug gap.

The question is does Jaguar use such a system on all their engines?

Bottom line is the engines are designed to run on our premium fuel, which is Europe's regular fuel. You cannot buy 87 PON gasoline in Europe and all their engines are designed to run on 91PON minimum octane rating ( over there it will be marked as 95 octane as they use the RON actual number, Pump Octane is an average calculated number between Motor Octane and Research Octane).

 

My newly purchased 2nd car is a Infiniti EX35 with the VQ35HR engine (297 BHP with a 10.5 to 1 compression ratio) and premium 91 octane gas is recommeded for best performance, but not required.

Due to a gas station premium pump being out of service I put in 10 gals of mid-grade (89 Octane) on an almost empty tank. NEVER again...the engine had a noticeable decrease in power, response, and smoothness.

If the manufacturer recommends it, stick with the recommendation...... it's there for a reason (optimum performance)!

 

I think there is a difference in mpg between regular and higher octane gas.

 

In fact the 89 is just pumped 50% from the 87 tank and 50% from the 91 tank. There is no 89 actually.

 

Also you get better fuel economy from regular gas because it has more energy per unit mass than high octane gas. this is ONLY if the engine can adapt properly to lower octane, turbo or supercharged engines can. Otherwise, you are just losing power because the high compression engine retards the ignition to accommodate the low octane, a double whammy.

 

Based on this I would imagine in the rocky mountain states, where some gas stations have 4 options- 85, 87, 89, 91....they must do rough guesses to make the 87s and 89s like, 2/3 of 85 and 1/3 91 to make 87 hahahah