I have the XJ SWB version and I average 12-13 mpg in the city and 19-20 in highway/continuous road with very few stop lights. I am not a heavy gas pusher only at times. What is your average? All answers are welcome including the 385hp version. Does changing gas (regular plus premium) impact your mpg and do you hear knocking noise in your engine?
Thanks all for participating to the survey.

 

The Wife's 2012 is getting about 17-22, mostly light street driving.. But it still has less then 400 miles on it..
We always use premium in the Cats.. Period..

 

12-13 city seems low. Could it be that you're using 87 instead of 92 or 93?

 

My XJL has 21 mpg avg. That's combination highway and city driving. Always use 93 gas.
It's also not super charged.

 

Per the trip computer, I average 16.8 mpg overall on 91 octane. My daily commute involves some pretty steep hills and I have somewhat of a lead foot though so it tends to bring my average down :-)

I've never used 87 or 89 octane but I do notice a slight difference in brand of gas though. The Jag seems to prefer Shell and 76 brand but my MB prefers Mobil and Chevron (the 4 gas stations closest to my house). I see a 1-2 mpg diff in the brands. Never understood why though.

 

My wife averages about 22 with either full throttle or full brakes...only Shell Premium 93. I don't even remember the last time I purchased 87 I've always thought premium was go fast gas... I use to even put it in my lawn mower.

 

Wow, you guys averages are great. I drive in a very urban situation with a stop signs or a red light once every two blocks. I use also premium gas but could not do better than 12-13 mpg in the city and 20-21 in highways. I hope I could have your averages! I typically put 33.5 psi on the front tires and 32.5 psi on the rear tires.

 

on highway ill get like 22mpg.
in the city ill drop down to 14ish.

ABSOLUTELY DO NOT FILL UP 87!!! yes you will see lower figures...and worst of all you will lose power. why buy a nice jag if you're going to restrict power. When we had the hurricane, i had to fill up 87 for a week and i could feel a night and day difference.

 

I drove the car through Houston traffic today and got 18mpg. Lots of stop and start. With the Escalade. I notice a couple mpg difference in using bargain 93 and Shell or equivalent 93. I am not sure how the stock tuning is on these cars, but often times with forced induction, to maxamize horsepower, you will add in timing to squeeze out power. Increasing the octane will help fight detonation. I am sure the knock sensors will do their job as well and will just rob you of a little horsepower. I believe 93 can be overkill in some vehicles, but with these SC applications is not. I still think 12mpg is terrible and would take it in to the dealer to have them go through it.

 

Your owner's manual specifically states that the cars are intended to use 95 RON (known as 91 AKI in North America) fuel, not 93. Using anything higher than 91 is just wasted money. Using lower octane may/may not affect performance and consumption.

 

Thank you all with your comments, I use 93 premium gas and I am disappointed at my gas consumption. In New York City, I sometimes average 11 mpg and the result is very disappointing. I use to have a Lexus LS460L and my average was 14 mpg in a comparable situation. I will try using Sunoco as it is rated 91 in NJ and see if there is a difference in perceived noise, performance and consumption.

 

I have a 2011 XJL. This summer took a 7,000 mile trip driving from Charlotte, NC to California. The trip included a lot of city driving in the San Fran and LA areas as well as driving the Pacific Coast Highway with many stops at scenic overlooks. Also lots of stop and go through Yosemite. Per the trip computer, I averaged 28.0 mpg. I calculated mileage manually for a couple of tanks and came within 0.2 mpg of the computer.

Octane ranged from 93 in the east to 91 in the west with one tank at 89 which was the highest offered at that Shell station. Drove about 5-7 above the posted speed limit.

 

My summer averages for 90 percent freeway driving and 10 percent tight hills + city was above 27MPG for my normally aspirated 2012 XJL. During the last two months, likely due to changing to winter fuel formulas, my MPG declined into the high 25MPG range.

I've never tried less than 93 octane. I know that most computers can adjust the timing for lesser octanes but, my understanding is that if a manufacturer states that 93 octane is "recommended" than it would be optional to use lesser octane fuels. If I remember correctly our owner's manual does not state an option so, I will not risk my warranty.

As to the degree of potential power loss by using lower octane fuel, my only experience was from owning a 270+ HP V6 Nissan Altima. It did say in the owner's manual that if the recommended 93 octane was used vs. 89 octane, the HP difference was only 7 HP. Higher octanes are important when placing the engine under heavy loads, such as pulling uphill and running at high engine RPMs or, chiefly, for boosted engines.

Albert

 

Here's what the owner's manual actually says:

OCTANE RATING
The minimum octane rating for fuel used is 95
RON (Research Octane Number). The vehicle
will run on lower ratings, but it may cause
pronounced engine knock or pinking. If the
pinking is severe it can cause damage to the
engine, fuel and emission control systems.
Note: Occasional, light, engine knock
experienced while accelerating or climbing hills
is acceptable.
Super Green Plus 98 RON unleaded fuel (where
available) may be used as an alternative to the
standard 95 RON unleaded fuel.
Some countries have only 91 RON fuel
available. Vehicles sold in these countries are
specially calibrated to use this fuel.

As noted in a previous post, 95 RON is the equivalent of 91 AKI. No mention of requiring 93 at all.

 

The owner manual says 91 or higher should be used.

 

In some parts of the US like here in SoCal, 91 is the highest available.

 

My mistake with the 93 number. Wrote my post from an airport. Now that I checked in my manual, you are correct, it does state that lower octanes (min. 87) could be used with CAUTION. Like I said that may be acceptable for light throttle applications but, I would definitely NOT use lower octanes for a supercharged engine. Supercharging or turbocharging raises the effective compression ratio, which requires the higher octanes. One heavy acceleration in a boosted engine may damage an engine with the wrong fuel. Don't ask how I found out about that...

Albert

 

Again from the owners manual:

Note: Occasional, light, engine knock
experienced while accelerating or climbing hills
is acceptable.

You may wish to contact Jag and have them correct their statement.

 

2011 XJ SuperSport 18,500miles

I live in the country so no city driving.
Highway will run 17 to 27 mpg and high speed really doesn't matter.
Its more about type of road.
Gas - is never under 92 octane.

 

I had a 2006 C6 Corvette with a blower, etc. I had a half of a tank and took it to the dealer for a recall. I picked up the car with a half of a tank...I did not check the mileage in or the in/out mileage on the receipt. I drove to meet some friends for lunch, on the way out I decided to get on it. That was the last time that engine was 364ci, it was towed to the shop for a built 402ci with meth. Needless to say, they drove 50 hard miles after replacing the right output shaft and filled it back up with the dealer pump. Nothing I could do about it, however, I sure did learn a lesson...plus I really enjoyed the 402 with increased boost