In the manual of my 1987 XJS V12 it mentions that the car needs 90 octane. But there is a major difference between European rating and American rating with European 95 being more or less equivalent to 87 American octane. Does anybody know if the manual relates to European or American octane?
Thanks,
Daan

 

My 87 US spec owners manual says 87 US octane is what is required, but I still run premium. And 87 US octane is closer to 91 Euro not 95 Euro.

Jon

 

North American spec HE cars don't need premium, which I always found odd as the Lucas cars have 11.5:1 compression. I run premium in mine.

 

I run our 98 octane, BUT we got the 12.5:1 engine, so choice is a no brainer, albeit $2.54/ltr bites a tad hard.

 

^^^
And here we are complaining about our local $6/gal for premium!

 

Try 8 dollars a gallon equivalent here!

 

does the 12.5:1 version require premium? What does the manual say?

98 ron is equivalent to 93 in North American gas.

Canadian taxes have slowly driven our prices up as well. 91 (AKI) is over 2$ a litre here.

 

I am "breaking in" my 39k XJSV12 1987 garage find, which went through a long process of restoration. It probably had not been run for 10 - 15 years as it was abandoned in a large storage facility. When it finally ran, it had a loud knocking sound and I feared some of the valves were damaged. But my mecanic told me to drive it for a while with injector cleaner, which I did, while using 94 octane. After about 300 miles the knocking sound had disappeared! I will continue high octane gas with injector cleaner, but maybe after a thousand miles, I may first stop using the injector cleaner and yet another 1 or 2k miles use a lower octane fuel. I am a very conservative driver and avoid fast accellerations or high rpm. I just want my car to look pretty . I guess that when the engine has been properly cleaned, my driving style does not really require the highest octane.

 

Your car your choice.

NOT MINE TO DICTATE.

Run the highest octane available at the pumps. We NO GOT Ethanol more than 10% readily available (85 is a look and hunt task) down here, whoopee,, and I run our none laced 98 in all of them, no matter the engine, or the book.
Books CANNOT be updated, common sense, and the info is based on what was the brew of the day when it was printed.

Injector cleaner, is a bottle a month in ALL mine, Infected or Carbied, its just a habit from the Redex days, like a meat pie without sauce, yuk.

I buy the stuff by the carton, whenever its on special, and brand means zilch, its the same stuff inside.

Never replaced, or cleaned, any Injector in all my years. The Carbied beasts are always clean as new whenever I need to look inside the bowl etc.

Driving it as you are is my strong advice. The V12 was built to RUN, and RUN HARD. So when you and the care are better aquaited (AKA the warm and fuzzies), Vegas and back, the BEST thing you could ever do for the beast.

 

I will take the advice on the octane, but I drive my 3 oldtimers, my 1987 Jag, a Citroen prestige 1987 and my Buick 1930 with tender care. I consider the all museum pieces that should be passed on to next generations of car enthusiast after I pass away. So I drive them on cruise control as much as I can, don't accelerate hard, while I enjoy the envy looks of modern car drivers, as my jewels gently slide along the roads.

 

God for you.

That will workwell with teh 3 you mention, but the V12 being an "over square" engine will labour at that.

It was design to run, and rev.

All my Jags since day 1 were Daily Drivers, and we lived miles (in those days) from anywhere, so pedal down and get on with it was the flavour of any trip. Mostly on unsealed roads.

I still have some of the early beasts, allocated to the kids, and stored in a barn for when I go on that big trip. They look after them, its the deal.

The best is the 85 XJS, that sucker took us twice around our island coast road (25K kms each time), and was the best road trip/s we did before age got us, not the car.

 

As you wish but, actually, you're not doing the engine....nor future generations.... any favors.

Cheers
DD

 

I let all mine kiss the Red Line every shift just to keep the spider webs out!
(';')

 

After a lot of work has been done to the car, it works fabulously. It has new fuel injectors and all runs incredibly smooth. As I feel I should drive a 35+ years old car gently, I drive it as much as possible on the cruise control on the country roads where I live.. Originally I drove it with 90 USA octane without alcohol and injector cleaner. As the car now has been used for some 1500 miles since restoration, I switched to regular with alcohol and don't feel any difference. Of course that is with my conservative driving style of about 50 - 55 mph depending on the speed limits, where the car hardly ever kicks back into a lower gear even on the many hills where I live. On the highway, which is not often, I drive it up to 80 miles when I can, and again it runs fine on regular 87 US octane. I am just not sure if I should continue using the fuel injector cleaner, now that they have been replaced. The car uses quite a bit of gas: 14 miles to a gallon is all I get even with my conservative driving style of mostly around 50mph.

 

I see no harm in continued use of the F.I. cleaner. Opinions will vary, of course.

With your very gentle driving style you may well get by with the lower octane. The whole idea of the higher octane is to prevent knocking/detonation/pinging. If your engine isn't pinging then the money spent on higher octane is wasted.

If I understand you correctly your reported fuel economy suggests something wrong. If your reported 14 mpg comes from steady speed cruising, with the cruise control, at 50-60 mph, you should be closer to 20 mpg.

When I had an XJS (an '88V12) I used it primarily for long highway trips and 17-20 mpg was the norm. Under ideal conditions 21-22 mpg was possible.

City driving was another matter. And driving with gusto is another matter.

I'm speaking in terms of USA-sized gallons, by the way

Cheers
DD

 

There is no pinging at all, so I am good there, but yes the milage is very low indeed, much lower than the specs on that car should be, and indeed, I drive very conservatively, mostly distances of 20 miles at the time. Any suggestions on possible causes? The valve gasket has been replaced, as well as the fuel lines, and the sparkplugs...

And yes, US gallons. As a Dutchman, I hate the American Standard measurement system, but what can one do in a country that still measures with a medieval system.....

 

Driving only 20 miles at a time? That's not enough for your fuel consumption measurements to be meaningful

Forget what I said earlier.

Get it on the highway for 100 miles and see what happens

Cheers
DD

 

And when you are doing the 100 miles, give it some beans! V12s need exercise!

 

American octane is motor method plus research method divided by 2
British octane is just research method. So British 95 octane is a point or two higher than our combined divided by 2 method.
When you add alcohol to the number, it’s rated lower technically then it is. I say pure ethanol has a 105 octane but it’s not really. Alcohol is both higher and lower but not rated by octane.
The engine will ping less with ethanol and run cooler but that’s because it’s a slower flame front.
That means the expansion of gases occurs further down the stroke of the piston.
Long strokes ( 4” ) develop more torque with alcohol all things being equal.

 

Thanks for the great advice. When almost empty, filled it up with 90 octane alcohol free and addid some additive. I took it to the nearest highway and just before entering I topped it off, to make sure I had the true milage. I drove it for 99.5 miles at a speed of 63 mph plus or min 2 depending on traffic. I took it to the nearest gas station after the exit and filled it up: 4.7 gallons, which comes down to 21mpg. Amazing, but also a bit worrying. For the kind of driving that I need it for, which is contryside driving, it is very thirsty. In fact, the previous tank fill, it only did 9 mpg. But heck, gas is cheap in the US!
As to the other advice, I am very reluctant to give it some exercise. It is an old car, and wear and tear are just significantly higher when driving more aggressively. I ruined the transmission of my previous Jag, an XJ Vandenplas 2000 with only 50,000 miles in just 10,000 miles after I had bought it. (It's live ended when rear-ended and totalled, which had nothing to do with my driving style). But for this Jag, I decided to drive it gently.