That's an unusual story. I can't imagine any reason why octane rating would affect the car in the manner you describe. Jaguar recommends 91 octane for the car, using anything higher is a waste of money.

Possibly the 90 octane you had was contaminated in some way but the octane rating would not have been relevant in that eventuality.

 

Yeah I use either 91 or 93, I've tried both 87 and 89 once and they both made the car run like crap.

Some gas stations don't have 93 available so I'll use their 91 instead, but I usually find that stations with 93 (like Sunoco) offer it for cheaper than the 91 of the stations that don't have it. Plus when I filled up a few days ago, 93 was 2 cents a gallon higher than 91 so there was really no advantage in using the lower grade

 

Angel, I am finally off of my long hours (just got off at the end of last week). So, if there is a time that will be good for you, let me know. We will get you taken care of.

 

I have read this post. I'm considering a 2004 X-Type 3.0 with 174k miles. I wouldn't consider running regular gas (87 octane rated). My question (or my wife who counts our pennies wants to know) would the mid grade (89) suffice? I know we are just talking a small amount of $ per fill-up, but like I said. She counts our pennies.

I saw the post to 'try' a half of a tank of mid grade, but with high milage I don't want to do that if it might hurt the engine.

By the way, the car checks out nicely. It seemed to have been babied for its 174k.

 

Then the costs of maintaining an old Jaguar will keep you in the dog house permanently.

The octane discussion go around in never ending circles on every car discussion board. What comes to light quite frequently is the lack of understanding of why some cars need high octane fuel and most don't. Good luck sifting the truth from the garbage.

 

Kink of what I though about the octane. I won't skimp.

As far as the maintenance - like I said it was babied, AC compressor was changed, transmission fluid is clean and changes smoothly, brake caliper change about 20k miles. Taking it my mechanic this afternoon for a complete check-up.

I do my own oil and other automotive bodily fluid changes, brakes and most anything that doesn't require a teardown and if it does my guy can handle it and he charges me next to nothing. But still waiting on his word before I pull the trigger.

 

Run it with the higher octane if you buy it and see how the performance and MPG is. After a couple tankfuls run a half a tank at the lower octane and see what you get. If it doesn't perform as well in your specific car and/or the MPG goes down (provided the way you drive doesn't change) then switch back. If it's fine, run it. Keep in mind that if your MPG goes down and you don't notice any real change in performance then the pennies you think you are saving are even less. You won't damage the engine.

Like Mikey said, this comes up every once in a while and has been "debated" ad nauseum, although I have to admit, it has been quite a while since I remember the last discussion about this. The only thing that gets beaten around here more is the synthetic vs. dino oil debate.

 

At 10.5:1, I'll stick with the premium.

I have found something that DOES make a difference: we have a station here with 93 octane gasoline. No E10 like everyone else has. No ethanol at all.

I've A-B'd a number of tanks.

Performance-wise, just a tad, consistent, but not significant.

However, it allows more overall timing, and provides a very consistent 2.8 mpg improvement in the city. On the highway, at 75 MPH, the difference is a solid 4+ miles per gallon.

Oh, it's .25/gallon less than the E10, too!

Too bad the car has cats...I used to run my muscle cars on 110/120LL Blue right out of my wing tanks. That was 12.5:1, though.

 

The difference in mileage you observe is due to the 3% higher energy content of pure gas vs. E10 and not due to any difference in timing. Both fuels are 93 AKI........

I'm surprised that pure gas is cheaper than E10.

The engine achieves full performance on 91 AKI (95 RON). Using fuels higher than that is just wasted money.

 

Mikey, I monitor in real time.


DEFINITELY more timing available up high. Almost a full degree. On the E10, the knock sensor stops the curve dead the second it hears a chuckle. On the straight gas, no chuckle, so no foldback.


I suspect that the swill that they sell us around here has closer to 15% ethanol, so the BSFC improvement is pretty consistent with that.


I really do miss real AvGas. Everything is certified for Hi-test auto gas now...just no alky in airplane juice.


I get close to the same mileage increase in my 3.8 Chrysler, regular for regular. That car, increasing the octane doesn't make a difference to speak of, but more energy in the fuel sure does.


Have you priced ethanol lately? Yes, it is more expensive than gasoline!

 

Wholesale prices (as of today) are $1.55 per gallon for ethanol, and $2.02 for unleaded gas (87 octane). Prices for ethanol rarely approach those of gasoline. If you are paying more for E10 fuel than straight gas, someone is ripping you off.

 

Yeah, the government and the distributors. Put the ethanol into fuel, and the commonwealth adds road tax to it, and the dizzys charge to mix it in!

PA has the second highest gas taxes in the US.

By the way. $1.55 is the subsidized price.