Hi

I have my 2000model XKR and also run a 2010 5.0L XJ

I'm just curious as to what type of unleaded petrol people are using, whether it's the standard 95 RON or the Premium 98 RON, and anyone's noticed any difference.

The reaon for this post is that I've been running my XJ for 12 months now using the standard unleaded with no thoughts of using anything better.

When I recently purchased the XKR the previous owner who had it for 7 seven years had been running it on the Super Unleaded and recommend I carry on doing so.

Your views on this and what you use will be appreciated.


Kind Regards

Rocky15

 

I think your owner's manual specifies 95 RON petrol. The car will achieve full rated performance with this fuel. Using anything higher will yield no benefits.

 

95 RON works for me. I use 98 RON when I'm on a road trip and 95 isn't available. Can't see any reason to spend an additional 6-8 cents per litre for 98 when the manufacturer recommends 95.

 

I'd use 95 (and have done for nearly 7 years in my STR) unless the car is meant to be run on 98 (which I doubt even the 5.0 is).

BTW, it can be a lot more than a few cents here for 98!

For track use I might investigate whether 98 did anything. (Expect to be disappointed.)

 

Jaguars are calibrated to use the fuel available in the country of sale.

Here is the UK, the recommendation for both of your vehicles is unleaded petrol 95 RON or higher. Given that 95 is the readily available standard, I wouldn't think of using anything other.

I've occasionally used 98 RON in a number of Jaguars with no discernible difference other than the cost. The only time I do notice a difference in performance is with the E10 on the Continent where there a marked drop.

Graham

 

The difference is the Ethenol content which I think is at least 10% in the US rather than 0-5% in the UK (not sure about Europe). Ethanol is basically bad for all sorts of bits - there's much been written on the subject already, here's some info for older cars.

Fuel Information

 

Many thanks for all your replies. It's what I thought


The guy who ran the XKR for seven years before I bought it has probably thrown money down the drain and donated more to the taxman

 

My '99 XK8 4.0 in the US requires premium fuel, 91 octane of higher. Regular has an octane listing of 89. As this engine has a high compression ratio and the fuel here in the states ( my opinion ) is poor ( bare minimal federal detergent requirements) , I use 93 octane premium. My XK8 drop top is a spare vehicle, little mileage per year and I'd rather not take the chance with either 89 or the 91 product. Rich

 

Since I stopped using Tesco 99 ron my error P1033 messages have stopped (P0133 sensor circuit slow response bank 1 sensor 1) . This might be complete coincidence. But I was told that Tesco buys their fuel off the military and its full of additives which play havoc with things.

I'm no expert and this may not have a baring on fuel used. Just saying.

I just use regular 95 now with no trouble.

 

The OP is in the UK where the octane rating is expressed by the Research Octane Number (RON). North America uses the Anti Knock Index (AKI) number.

Rule of thumb

95RON = 91 AKI
98RON = 93 AKI

Your car was built to operate on 91 AKI. Anything higher, as in the OP's case, is a complete waste. Octane rating number has nothing to do with with the volume or type of cleaning additives.

 

A few years ago the Southeast US experienced a severe shortage of anything other than 'regular' fuel that lasted several weeks. During that time I researched octane and engine requirements and came to a conclusion.

The Jaguar design with knock sensors measure pre ignition 500 times per second and adjust the timing accordingly. Five hundred times 60 seconds is 3,000 rpms.

I think that means that between the sensors and the ECM pre ignition is managed at the expense of power produced.

Bottom line is if you expect to develop the advertised horse power use the recommended octane. If you drive like I do 89 regular is perfectly adequate with absolutely no negative affects on the engine. I rarely hit 3,000 rpms.

 

Thanks for relating your first hand experience. There's occasional discussion about the use of lower octane fuels with many owners believing that the engine management system cannot cope with such practice.

I don't quite follow your logic of the significance of 3000 RPM. At that speed, each cylinder would fire 1500 times per minute or 25 times per second. If a knock sensor samples at 500 times per second, it would 'hear' each detonation (not pre-ignition) event 20 times. Plenty of safety margin.

 

I would think that each detonation would provide an opportunity for the knock sensor to produce a pre-ignition event thus adjusting advance at many times the rpm of the engine.

 

You might have your terminology confused.

Detonation (knocking/pinging) is what the knock sensor attempts to eliminate by retarding the ignition. Pre-ignition is not part of the game.

 

Yes, you are correct. Incorrect usage of 'pre-ignition'.

But the knock sensors do operate at many times the opportunity for knocking/pinging to occur.

 

Agreed. Far faster, more accuarate and more sensitive than the human ear.

 

On the other hand, there is a measurable and repeatable increase in MPG
when using premium. With a price differential between regular and premium,
the resulting MP$ can be competitive.

It's a have your cake and eat it too scenario.

Then again, I run down the highway with sport+4 because the instant
throttle response is nice. No different than if I really had a 3.58 rear.

 

I use straight gas, no ethanol, 89 octane. Car runs great.

 

Yes, here in the States, Octane levels are the only gauge we can go by. My owners manual as well as the fuel ( petrol) door on my vehicle also states Premium Required.
As per John W from Wales stated, Europe uses 0% to 5% Ethanol. In my State, 5% is required with 85% Ethanol available. No option.
Even at a 10% Ethanol, fuel mileage as well as performance is greatly, greatly reduced when the fuel is new/ fresh. Ethanol not only absorbs moisture, it attracts moisture with time. The older the fuel the more moisture. Try it with E 85. Gotta be a 30% loss in mileage. Not to mention corrosion with fuel lines/ poly tanks, etc. The Feds are pushing for 15%. Anyone who has a boat knows the problems Ethanol is causing.
Me, I will continue to use the highest octane at the busiest stations available.
My owners manual also states use only fuels which contain detergent additives.
Fuel I use has 5 times federal ( US) requirements. Meaning. Minimal detergents with higher carbon build up with most fuel sold. Rich

 

The OP made no mention of Satan Ethanol, strictly octane ratings. Why has it been dragged out for another beating?


No Jaguar is rated for use of E85. There is specific mention in the owners manual NOT to use any fuel greater than 10%.

Many high octane fuels contain 10% ethanol.

Again, detergent levels have no connection to ethanol content or octane ratings.