I recall that Jaguar recommends using premium gas, but does that necessarily translate to 93 Octane? What do you guys use in your XJ6? I don't mind paying for the higher octane but if it's not necessary, I won't put that in. I am used to cars using 87, unless they start pinging.

I did a search and nothing came back for the X300. If this has been asked before, my apology then. Thank you!

 

Your Jaguar is rated for 91 octane or better - translation for best overall performance - 93 Octane - now I've heard of people switching between 89 octane and 93 octane when filling up to get that 91 octane "mix" - hope this helps...

 

Hi abonano, thank you. That makes sense... I will stick with 93 then. Alternating would be ok, but we probably need to do it at half tank to ensure a good mix.

 

My '96 3.2ltr has a sticker inside teh fuel aperture that states:

" Use Premium 95RON Unleaded fuel only".

Now this may be a sticker for my market??, due to our 3 versions of unleaded fuel being rated at 91, 95 & 98 RON.

I use 98 unleaded in ALL the Jags, no exceptions.

 

I asked my brother, a petroleum engineer, about this long ago and he chuckled and said, "It doesn't work that way." I never asked for an explanation, since I'm not a PE.

 

Sunoco sells 91 and 93 octane gas in my area. Since the price differential is only about 2 cents a gallon I get the 93 octane blend.

 

The octane question comes up almost daily but in all sorts of weird and wonderful ways. Jaguar says 95 RON which equals 90 or 91 AKI for us in North America. Anything higher is a waste of money with no benefits.

 

In the US, we have mostly three choices: 87, 89 and 93. Sunoco is the only one that sells 91. So really no choice but to go with 93.

 

OK, but I'm surprised. My other fun car is an old Corvette and all I read about is guys in the US not being able to find 93 at all (?)

Please ask him then how it's possible to obtain low, mid and premium grade gas at filling stations when there's only two underground tanks.

 

I'm thinking he means it's not simple as half 89 + half 94 = 91. Again, I didn't ask, didn't want the long engineer's explanation - it gets painful

 

Regional difference. On the east coast and midwest, we get 93 octane. I hear out west, they get 91 instead. Someone from California can probably make an excuse and drive to a gas station to verify?

 

I've been curious about the octane selection as well. I sometimes get the 108 Octane Booster for my 2004 XJR 4.2L Supercharge. Is that ok? I mean I haven't seen any issues thus far...Just curious.

 

Your car was engineered to achieve peak performance on 91 octane, anything higher is money wasted with NO return.

 

Mixing low octane fuel with high octane will not give you a medium grade octane. The molecules will be either 87 or 93. They do not reformulate in your gas tank.

An underground fuel storage tank can be multi-chambered. Holding two or three grades of fuel. Most gas stations don't have property large enough for 6 underground storage tanks. 87,89,93,e85,diesel and sometimes kerosene.

 

I put 91 in because its available and that's what the manual calls for. anything more is a waste of money.

 

We're drifting off topic, but if you do even the most basic search on the topic you'll find that the octane rating of fuel is achieved by the blending in of additives which is far from being at the molecular level. Whether this is done at the refinery as the delivery truck is being filled or at the pump by blending the contents of two underground tanks makes no difference.

The famed Sunoco 190-260 range of gasolines back in the '60s was achieved in this second manner, so the concept is nothing new. It's very common practice today for someone to add some 108 'racing' gas to a tank of 91 octane to satisfy the anti-detonation needs of an old school high compression engine.

 

Generally I'd agree, but if for some reason you have other factors inducing knock, then a higher octane fuel can help reduce knock and any induced knock reduction (which usually translates to lower performance/efficiency) from the ECU.

Some other factors could be a malfunction, which I'd agree then would need to be repaired instead of covered up by higher octane fuel.

But in theory a very hot environment could contribute too. So it may be possble that in a hot climate higher octane fuel could help reduce knock.

And of course, anyone modifying something like boost levels may need to look at higher octane fuel if they are seeing KR.

In the absence of 91 octane fuel though, I'd get 93 to avoid any knock issues. That's what I have to do with my 95 Eaton SC'd Riviera too.

Al



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I use 89 in my XJ6 with the crank sensor mount mod. I don't try to drag rice burners at the lights, so any loss of power is not noticed and there is no preignition knock. Mileage may be slightly lower, but I have not been able to see a difference.

 

As ever with threads on this topic, widely differing opinions will never result in a clear conclusion. Go with whichever rationale you feel makes most sense. For me that means using the fuel rating recommended in my handbook. That rating was determined as optimum for a reason, by Jaguar engineers who have most likely forgotten more than I will ever know.

 

Agree completely with that statement


If I can find 91, I'll put it in, right now we have 87, 89 and 93 as our only choices here in my neighborhood until then though.



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