Octane Fuel for Jaguar?
 

Hi guys,

What octane number fuel would you suggest for Daimler V8 Super 1999? And what do you use?

95 or 98?

At this moment, I am using 95 Futura.

Fuel
 

I used to think it didn't make any difference. That was until I had to pull the heads and do a valve job on my Land Rover due to sticky valves. Now I use Chevron or Shell premium (highest octane) in both my vehicles. The Jag manual recommends only premium unleaded. I think it's false economy to use anything less. Just my opinion.

Yes, but back in 1999, not sure if there was a 98 fuel. Higher octane fuel won't cause any troubles, right?

Fuel
 

I think we're talking apples and oranges here. In Europe they have a different octane rating method from the U.S. of A. What they call 98 octane is our 93 octane - I believe. You can't get any higher than 93 here in the U.S. at a regular filling station. It cetainly ain't gonna hurt anything to use the highest octane in a Jag. That's what they recommend for it.

Agree with JimmyL's SECOND post but not the first with respect to the low octane= sticky valves. The octane rating of a fuel has nothing to do with the amount of 'cleaners' or any other unrelated additive.

This subject always brings on a lively discussion so I will pour on a little gasoline on the fire.

In late '08 the Southeast US had a severe gas shortage and only 'regular' fuel, 89 octane, was available. Until then I had honored the Owner's manual on using 93 octane. I could not perceive any difference with the 89. Since then I have tried to measure any difference in mileage between 93 and 89.

None.

The knock sensors are sampled about 500 times a second and instantly adjust timing to effectively manage pre ignition. I do not drive aggressively and never ask for the horsepower potential of the engine.

I have switched to 89.

If I had an XJR/XKR and drove aggressively I would probably have a different opinion.

On with the debate.

With the state of intelligence embedded in modern automobiles, I don't think a debate is necessary - you are correct.

With the knock sensors detecting pre-ignition due to lower than specified octane levels, the timing will be retarded in order to stop the knocking... so performance will be lost. If you're not into performance, you're not likely to see any difference.

It's that one time when you REALLY need to tromp on it, in order to avoid that semi-truck that's barrelling down on you... and the split second of lost performance due to the knock sensor induced timing retardation, that you might notice - "Damn, why didn't I fill up with Premium!"

I hope none of us are ever put into that kind of situation.

Fuel
 

Like I say, just my opinion. And I think everybody is correct about the power and the additives and the knock sensors. I was under the impression - maybe incorrectly - that low octane fuel does not burn as completely as high octane fuel, therefore, the exhaust valves would get more carbon deposits on them with low octane fuel as opposed to high octane fuel. The reason that the timing needs to be retarded to prevent knocking with low octane fuel is because it burns quicker than high octane fuel.

Well, I have full tank of 95 atm, once it's finished, will fill it up with 98 and see if there are any differences.

Not true at all. Gasoline burns at the same speed and temperature irrespective of octane rating. The purpose of the rating enhancing chemicals is to reduce the tendency to pre-ignite (ie before the spark plug fires) whether due to hot spots in the combustion chamber or simply the heat generated by compression of the air/gas mixture in the combustion chamber.

What problems are you experiencing?

Presently using US Tier 1 mid-grade. No problems after switching from "high" octane grade.
Lower octane gas is more flammable than higher (less detonation inhibitors), I imagine it helps on cold starts.

If your V8 4.0 engine block is Nikasil I would consider using middle to high octane.

FYI = ALL AJ-V8’s produced between 1996 and 2001, regardless of size or application, (XK 4.0, XJ 4.0 and 3.2, S-type 4.0)

No problems.

Can highest (98 in our country) cause any issues in the future? Yes, it's Nikasil engine.

I have checked few other cars with Nikasil engine, and even older ones recommends using 98.

http://books.google.com/books?id=el6...%20ron&f=false

I think you need to read this http://www.gusglikas.com/AutoRepairNikasil.htm

I did, but it did not help :icon_emm: Unless sulphur has something to do with octane #

No connection between sulphur levels and octane rating.

I will do a little checking and get back with you.

From what I can find we are both correct in that the sulfur content is the same in regular and in high-test. However, high-test burns hotter burning off the sulfur faster and cleaner than regular.