What's the minimum octane rating we can use in the x-type w/o causing problems for our engine?

 

Can o' worms question. The manufacturerspecifies premium, which is 91 octane or higher (at least in N. America). Different countries use differnt methods to determine octane ratines (RON and so forth). Bottom line is that 91 or higher is what Jaguar says to use. It doesn't "recommend" premium, it specifies it. There is a difference.

That being said, you will find plenty of X type owners who run 87 or 89 octane all the time with no ill effects, myself included. Some say the only penalty is the loss of a few hp at the top end of the curve, while others will swear that you're gonna blow the whole thing up.

I run 3 tanks of 87 to 1 tank of 93.

 

What I've read is that the computers in cars these days will compensate timing-wise for the different fuel grade used. So you won't get that popping noise in the engine. What I read is that it shouldn't hurt the engine. Like you said, the HP loss is minimal and might not be quite as fuel efficient. I might try it and see if the MPG suffers. If it doesn't, saving 30¢ per gallon might be worth it.

 

I always put super in my car, you should get better gas mileage by doing so. So I look at it like I am getting something for the extra cost - fewer fillups a year - no?

 

I just filled up with 89 octane. So I'll track and see how the mpg are and if I notice any loss of power. I fill up once a week, so the savings per month will be $30. That's worth it to me if mpg doesn't suffer.

 

Since fuel prices went up, I've been interested in the possible differences between octane ratings vs. mpg. I've done multi-tank tests with both 87 and 93 and have found no significant difference in fuel economy. Biggest factor is still the judicious use of your right foot. Have not felt any "seat of the pants" difference in power either. That being said, I believe that a higher octane has a better detergent quality than lower octanes, and a tankful on a regular basis is a good thing. Just my opinion.

The motors in the X typesare not forced induction - therefore detonation (pinging)should not be that big of an issue.

 

Well if regular is $2.98 and Super is $3.19 and you put 13 gallons in - regualr will cost $38.74 and super will cost 41.47 = $2.73 difference - The medium grade would make an even less difference - why not just put in the good stuff no?

 

Please stop me when I am wrong here as I am no OBD-II expert, but it is my understanding that when a computer for a car is installed that is recommending premium fuel, the program for the timing assumes this grade of fuel and from the start has the timing advanced a few degrees with the intent of getting more power and preventing pre-detonation. Loss of power is not a big deal for most people, but the pre-detonation can be a big issue as this can lead to engine failure. I don't recall the compression ratio of our cars, but you get up near 10.0 or so, running a higher grade gas (ie, higher octane) is required to prevent pre-detonation. With the installation of a knock sensor (sensing the pre-detonation), the computer can retard the timing/fuel back to prevent this from happening. But, the computer can only compensate so much. I don't know if it is truely worth it. The price a month is minimal in my opinion for the added assurance that the motor will work as it was designed and not fail on me. Not to bring back an older topic, but look at the car and treat it accordingly.

 

Pull fuse 32 to erase the timing settings and force it to relearn the timing settings immediately (with Super+ in the tank) thus avoiding having to wait for a few tankfuls.
Ive tried Regular (95Ron here in UK) and Super+ (98 Ron) and cannot tell any difference apart from what Chris X said...worse MPG from Super+ due to putting foot down to see if it works.
Over here regular has come down from £1.19p/ltr (£5.40 per UK Gallon equivalent to about $10.26 per UK Gallon at $1.9:£1) )to 95.9p/ltr over the last week or two.Yes, thats right over $10 a gallon over here thanks to the govt 79% tax + VAT on fuel (I believe)!!!
Super+ is still over £1.10/ltr in some places so the extra paid over here wont warrant any savings claimed by the fuel companies.

When I had my MR2 Turbo it was imported from Japan where their std fuel is 102Ron (if I remember).
It would 'pink' like mad using 95Ron so had it mapped to take super+ (98 Ron).On that car using 95 Ron would wreck the engine due to the pre detonation ('pinking'), not an issue with the X Type.

 

Oh man Buck that is expensive - you must be rich to afford a car at $10 a gallon.

 

Its lucky I only have a 2 mile drive to work!

 

I just put regular fuel in my car.

 

I run 91 or higher..the OM specifially states DO NOT run anything less (Im pretty sure it says that), but if you have to, put only a small amount of low octane until you can get to a station to fill up with 91 octane or higher.

 

Its gonna blow up.

 

Unless it states that "use premium only" you may use regular from what I see . If you have your PCM reprogrammed then you should switch to premium .

 

I've seen this topic debated on about 20 boards with pretty much the same results as this string. No consensus will be reached, it's up to you as an individual to make a decision. Just like with politics, "facts" can be found for both sides of the arguement.

 

Ah, wasn't it the engineers that said FILLED FOR LIFE???

OK, I know apples and oranges!

 

well, just 'cuz I can't keep my big mouth shut... I'll throw-in my $.02

Years ago, I was racing a 2-valve, air-cooled Ducati. On the Dyno, this bike made as much as 4hp more with a mid-grade (88 octane) fuel, versus a 91, or even the 110 race fuel readily available at the racetracks. Even with the high compression. It seems the higher octane slowed the ignition / burn rate so much that it reduced cylinder pressure.
Now, when we added another spark-plug to the head, we ended-up with two flame fronts that solved that issue, and we were able to make more power with the higher octane fuels.

How does that translate to your Jag-oo-R?
It doesn't. But it's interesting anyways.

what DOES translate to your Jag though, is the fact that the QUALITY of the fuel you use is as important (or more so) than the octane rating.
Don't buy fuel at places that didn't START by selling fuel... like 7-11, or Grocery Stores... or WalMart. Buy fuel from a reputable refiner. My personla preference runs to Chevron, with the Techroline (or whatever they call it now) additive that maintains injector health.