A friend of mine is a MB owner (3 of them - all require premium fuel) and we had a debate over the weekend. He runs regular in all of them and claims he has read that with the exception of some reduction in performance the lower octane does no harm because the sensors adjust for the fuel. I've read the same thing and it does make some sense. But I also recall reading that, while your engine won't knock, the lower octane fuel can harm the catalytic converters. Personally, I'm leery of risking a high dollar engine to save a few bucks on gas. Furthermore, I can't imagine that car manufacturers specify premium just to raise Exxon's profits.

Anyway, I thought I'd throw this one out there and let some brighter minds weigh in on this issue.

 

I have only used 89 octaine from day 1 and both cars run just fine.

 

I have seen this question on all of the various car websites I have frequented and here is my stock answer. Let's say you drive 10,000 miles a year and get maybe 15 miles per gallon. So that comes to 667 gallons of gas a year--let's round that up to 700.

Let's say that you pay 30 cents more per gallon for premium versus regular or regular+. So that comes to about $200 more for using the premium. Is this really something worth fretting over?

Doug

 

I totally agree with Doug as well your friend needs to consider this!

With regular vs premium fuel, using the regular you get less performance and less gas mileage, in the end you really end up paying more for a car that drives worse and isnt as mechanically sound!

 

Guys,

Here is what happend to me (you might not like the car) I had a new Crossfire and filled it with 91 octane instead of 95 just as the dealer (Chrysler) told me. Performance was not that different having played around with 91 and 95 excepting that you get better fuel/millage from 95 octane. However, here is the crunch after 40K KM the exhaust started making a strange noise, which then turned into a rattle which became so bad it I had to take the exhaust system apart (this was not a warranty item). The car had two Cats either side of the V6 engine the lower cats were found to be in pieces both having collapsed completly. The cost of each Cat $2,500 NZD. I am not going to say what I did to fix it however, that is the risk, fortunatley the gas sensors are foward and either side of the primary Cats so no engine managemnt issues, other cars such as a BMW would have left no choice but to replace them.

95 octane is the only fuel going in my 97 XK8.

 

You need to perform your own test like I did and then make your choice. You can see my results on my page under MPG.

 

Doug, the price premium for premium fuel is now $0.60/gallon. With regular fuel at about $2.00/gallon, premium fuel comes with a 30% price premium. That is insanely steep.

I do not have an R model, and I rarely use more then half throttle. It'd be nice if a Jaguar tech can authoritatively declare the need or discretion for premium fuel.

 

You've dug up a thread that's been dormant since 2009. Many of the participants are long gone. The octane issue has been thrashed to death dozens of times since then.

Please refer to the most recent beatings/lynchings for additional info.

 

I think the response was directed to my post I'm still here

I stand by my analysis that it is silly on the one hand to buy a higher-performance vehicle only to fret about spending a few more bucks on higher octane fuel

Doug

 

A car with active knock sensing will retard the timing when detonation is detected. That could occur more readily on an R, but unless you are running a very high compression naturally aspirated engine, you are unlikely to invoke detonation under casual driving. Retarded timing will result is less complete combustion which will reduce fuel economy and also spill a marginally higher percentage of unburnt hydrocarbons into the cats. This could result in your cats running hotter, but that is highly unlikely to result in their destruction.

At the end of the day, if you bought a car you knew needed premium then suck it up and buy premium. If it requires regular unleaded, don't waste your money running premium.

 

I'm with Doug on this one. Lord knows I'm at WOT often enough.

I'll never forget the time I spent $$$ and bought 15 gallons of Sunoco 100 octane racing fuel for her. Was she faster? Well not like i added a supercharger. Probably a bit, but she actually sounded different. Added to driving experience for sure. What surprised me the most was increased gas mileage. Anyway, good memories for $10+ per gallon.

 

Yes, but that's not the question. I know the answer (and can prove it) but I'm not a 'Jag tech'.

 

Hey John--funny you should mention the 100+ octane. I am in the Los Angeles area and a number of years ago there was a local 76 station that sold 100+ octane but it was not at one of the normal hoses. You actually had to ask the attendant to dispense the fuel. At the time I had my 1995 Corvette which had an occasional missing problem (turned out to be plugs and/or wires) but on a whim I asked the guy to add a few gallons of the 100+ to my tank--I don't recall the price per gallon but it was much more than the 91 or 93 octane that was being sold as "premium". Even though the result was diluted, the car never ran as well--like a bat outta hell!

Doug

 

I have only used premium since day one in my xk8 (bought in 2011) and in my Z1000...

I may try using the lower octane on the Jag - but NEVER on the Kawasaki since I want TOP performance at all times on that

What I thought was strange/different (in that I have never seen it before) is that the owner's manual on my Equus clearly states that if you use premium gas you get 429 HP and if you use regular you get 420 HP (so I just use regular for that)...

 

You know guys, we forgot the most important issue with pump gas, any octane. In the USA, they dilute it with enthanol, 10% as I recall. Facts are facts, gasoline burns with more energy than alcohol. We are losing maximum power output because of this too.

To be honest, I should acknowledge that the "racing" gasoline has no alcohol in it at all, part of the reason Doug and I liked it so much? I've seen the calculations at 10% dilution of gasoline, one loses some horsepower.



John

 

Please don't drag ethanol out for yet another beating. E10 fuel has 97% of the energy of pure gas. End of story.


It's not related to octane rating of a fuel.

 

Mikey is right, it is 96.7% according to the govt. I looked at wrong column, not E10.

We were discussing delta between pump and racing, thats how this tired subject came up.

John

 

Now that we have resolved this can we talk about the best Oil to use... LOL

 

Okay, this is a tired subject, but I thought I would throw something out there and see if what I have heard is correct. I read somewhere a long time ago that regular (low octane) fuel burns faster than high octane fuel. Reason being that it is less refined, or doesn't have anything to smooth out the combustion so it just "pops" quicker and the fuel is burned up faster, and so it needs spark timing retarded a bit. High octane fuel burns slower but more completely, therefore the timing needs to be advanced so that we have time to take advantage of all the energy in the fuel.
Anyways, I always use Shell premium because I get a discount at the pump from my grocery store points. So, I'm okay with high octane. ;^)

 

Absolutely false. All gasoline burns at the same speed irrespective of octane rating. High octane fuel is more resistant to 'exploding' vs 'burning'. The correct term for exploding is detonation and is nicknamed knock, hence anti-knock index.

Octane is not how fast a fuel burns