I’m aware this subject has been of previous discussion, be that as may, I would just like some reassurance.

in the part of NZ where I reside you have choice of service stations all providing different Octane ratings. The majors have unleaded 91 and 95, some have 91 and 98, and my closest offers 91,95,98 and 100. Spoilt for choice. Because I travel in my 3.6 XJ-S in country areas that usually just have 91, or 95 I stick to 95 octane always.

My XJ-S was a direct UK Import and service manual refers to 98 only. Am I doing an injustice to my lovely Jag by sticking with 95 only.

thanks

mike

 

If it doesn't ping you'll be ok. It might be ok even on 91.

Higher octane gas "deadens" the ability of the fuel to ignite before the spark plug fires, hence the term "pre-ignition". High compression engines run on lower octane fuel have a tendency to compress the fuel/air mixture to the point where compression alone is enough to make the mixture fire, just like in a diesel engine. Adding ingredients to the fuel, (e.g. kerosene, tolulene etc) raises the octane rating making the fuel less volatile and therefore less likely to explode without the aid of the spark.

My XJ6, a Canadian model, runs perfectly fine on the lowest octane fuel available at the pump and has done for years -with no ill effects. It never "pings" or "diesels", so I never bother spending the extra cash on higher grades of gas.

YMMV

Larry

 

On the other end on the scale MY 94 will ping on anything less than 91. While that sounds low it's considered premium at my altitude (5-7500 ft) with the available options being 85-88-91

 

Yes well altitude does take it's toll. I think the "regular" I feed the car is rated 89

I'm about at sea level or slightly below

Larry

 

Octane ratings differ. In North America we typically see (R+M)/2 octane ratings, also known as the Pump Octane Number (PON), while in most of the rest of the world the Research Octane Number (RON) rating is used. The U.S. government explanation can be found here:

https://www.eia.gov/energyexplained/...e-in-depth.php

Additional helpful info is available here:

https://www.etuners.gr/fuel/

While the Jaguar XJ40 and XJ-S engine control modules can adapt for lower-than-specified octane fuel, they do so by retarding ignition timing, which has the undesirable effects of reducing both engine performance and fuel economy.

Also, the Jaguar straight-six engines are so smooth and these early knock-sensor systems so insensitive and unreliable that it is very possible that your engine may experience detonation or pre-ignition (two different types of spontaneous combustion or "knock") without your ever realizing it, leading to valve damage and other issues over time.

So I always use at least 91 and typically 93 PON fuel in our Jaguars, equivalent to 95 or 98 RON.

Cheers,

Don