I recently obtained a 1989 xjs and the dash says unleaded fuel only. I have been using regular unleaded and it rune fine, I read somewhere that you should use premium. Any thoughts on this.

 

For USA/North American market cars Jaguar says the minimum octane required for the V12 is 91RON. The 'regular' you are using is probably 87RON.

In other markets where the higher compression engine was sold I'd expect a higher requirement.

Watch for different octane rating methods, as not all countries use RON

The important thing is that the engine isn't knocking/detonating....which can cause damage.

Cheers
DD

 

Hi JaguarDon,

Not sure which part of the world you are in but in the UK regular unleaded can contain 10% ethanol (E10) which can cause problems with older gaskets and seals. Super unleaded is a max of 5% ethanol and kinder to older fuel systems. I have always use super unleaded in my classics and they seem to run better for it. More expensive but my annual mileages are low.

Here, regular unleaded is 95 RON and super 97 to 99.

Cheers,
LeeP

 

Experiences vary but if you can't find gas that is both high octane and ethanol-free, I'd be less worried about the ethanol and more concerned with the octane.

I've been running E10 in my oldie Jags for umpteen years with no problems; even my 1985 owners manual says E10 is OK. I think insufficient octane is a greater risk to the health of the engine, personally.

Cheers
DD

 

I’m sorry but you have bad information. Methanol isn’t poured on valve covers or or sealing surfaces. So oil seals are safe.
Plus you are confusing ethanol and methanol. Post WW2 methanol was often added to Low grade British Pool gasoline to bring the octane up with bad results to carburetor gaskets, aluminum and rubber hoses.
However ethanol and Methanol are both alcohols and for those who failed to pay attention in class that is the only thing they have in common. Ethanol as used in modern fuels is safe!!!! Methanol is not used in modern gasoline.
Ethanol is what people drink in Wine, beer, scotch, Bourbon, it’s safe. Methanol if you drink it, first you go blind, then you Die.
Ethanol Good
Methanol Bad.
One final point. Rubber used in fuel lines has not been legal in your lifetime. ( unless you are 106 years old)l. The problem Jaguar had with fuel lines starting in 1975 has to do with the pressure of EFI. The old Lucas Fuel line hose is fine at the 3 PSI used for carbs. Not at the 30 psi used in fuel injection.

 

LeeP
Let me deal with 2 other common misconceptions about Ethanol. Water. There has always been water in gasoline( no they don’t mix but even crude oil coming out of the ground b has water in it. That’s why once oil is pulled from the ground in the regions where permafrost exists they cannot shut off the pumping. If they do the water freezes and splits the pipe. Then they have to redrill and set another pipe.
Once in the tank air enters the vent and since air has humidity it’s reintroduced even after refining. Every tank right up to the gas station. Then in your cars gas tank too. If it sits there long enough the tank starts to rust . Since your gas tank has a vent in it to draw in air rather than contain a vacuum. The humidity in air will get into your gas tank.
Alcohol mixes with fuels easily. And because alcohol can absorb moisture it’s blamed for the rusting. 0K. Maybe some of it, 10% alcohol so 10% of the rusting.
Second Octane.
RON is research octane number. MON is motor octane number.
British fuel uses RON while
American fuels use RON plus MON divided by 2.
So our 91-93 is roughly equal to your 95/98 octane.

 

Hi to all, I own a 1988 and a 1989 MY XJ-S V12 USA specs Jaguars, I have both DRIVERS HANDBOOKS which show the following, first the one on the 88 and next the one on the 89... They say almost the same thing, but the later a little bit more easy to get straight...



And yes, I use 87 octane fuel...

Alfredo