new 2004 XJ8 owner here. When I bought this, I was hoping to get between 22-24 mpg on the highway, maybe 19 mpg in town.
The day after I bought it I went to Ohio which was 486 miles one way. I was kind of in a hurry to get there and along the way a new Challenger went flying by me so I used it as a lead car and fell in about 1/8th of a mile behind him. Because of this, I think it is safe to say I was going 90 mph almost half of the way there and I even got stuck in a mini traffic jam in Cincy.
My trip computer had me getting 29.6 mpg !

I did not believe it and stopped and put 4 gallons of gas in it just to see if the fuel gauge was really working - it obviously was.
I was stunned.

On the way home I was not in as big a hurry (and never had a lead car) and I would guess I drove about 78 mph the vast majority of the way.

The computer showed me at 28 mpg. I figured it was less coming back because while in Ohio a bunch of relatives took the car for a ride and they were getting on it pretty good, which obviously lowered the mpg.

Back home doing mainly in town driving, I am not speeding all over the place but I do pass cars going too slow very quickly and I am still averaging 27 mpg.

I really don't get it. It is rated at 16 mpg in town and 25 mpg on the highway for an average of 19 mpg,......

I have put about 1700 miles on it and am averaging 27 mpg.....

I am not complaining, but I really do not understand it.

 

The 6 speed tranny helps. Good to hear stories like this when gas is at a 'premium'.

 

78mph is almost exactly half speed, so the jag thought it was parked!

When I had a journey home on a spacesaver tyre, at 50mph, I got over 30mpg.

Short journeys down slow winding lanes, less than 20.

 

I used to get that good, until they started putting the alcohol in our gas here in TX. That reduced the mileage about 15%. Are you still using straight gasoline up there?

 

Normal, i always relate that to people about the car. You show me another full size luxury sedan with a v8 that regularly posts 30+mpg cruising the highway. The new jag doesnt nor the older, but the 4.2 in the x350 does that all day and is not a fluke to post high 20,low 30's

 

cjd - I have been using 10% alcohol gas.
I am down to about 26 mpg but has been all in town driving with only occasional bursts of speed

 

That sounds about right fr mine too. I always use premium and every 5 or 6 refills I dump sea foam in it to help with water /alcohol issues.
I have noticed it is better in hotter weather than extremely cold weather.
I curse when my average drops below 24mpg (A mode, reset every refill) in combined driving. In 6900 miles , my average is 24.9 mpg (B mode continuos).

 

One tidbit, many people aren't aware the EPA changed the MPG formula's for 2008, to make them more 'real life'. It effectively lowered the mileage ratings.

i.e. When our cars came out, they were rated 18 city / 28 highway.
As you stated, if you look them up, they are now rated: 16/25.

Here, you can see the difference:
Compare Old and New Estimates

I often see 28 on the freeway, would probably be higher if I tried.
*will be interesting to see what my tune up did for it.

 

I took a road trip from Dallas to New Orleans back in December. I filled up with Chevron in Dallas before leaving. Drove straight to New Orleans over night in the cold at 70mph for 520 miles to the last gas station I could reach. I purposely drove with the gas needle past E (nerve racking) to the last minute to try best calculate mpg. Computer stated 27.5 mpg. I calculated 27 mpg. Not bad for an 04 XJR.

 

average around 22 mpg highway with my 2004 XJR, which is exactly what the gov estimate is. I have Toyo Proxes 4 season tires on the car that are noisy and I suspect give lower mpg than some of the "highway" would provide. Considering making the change when the Toyos wear out. The beauty of the 6 speed transmission it does keep the revs down for steady highway cruising, typically close to 2000 rpms!

RyeJag

 

Like many others I was also impressed with the mileage I got from my 2005 XJ8L VDP. Over the two years I owned the car I averaged 31.8 MPG Imp and this was mixed highway and town use. The best I ever got was when I picked the car up in North Carolina and drove it home to Toronto Canada. 34.4 MPG Imp and we were not hanging around.


Boy I miss having that car.


Bob.

 

I purchased my '04 xj8 counting on this type mileage. In the month I have owned it I haven't gotten above 23 mpg driving all flat Ohio highway miles.
Congratulations to you. Maybe I am using lousy gasoline.

 

Best I ever got was 7.7L/100kms out of the XJR, that works out at 30.5mpg US or 36.6mpg UK but I was passed by everyone!

Highway cruising I usually see average of 8.5-9.5 but around town it's in the 14's...

I get better consumption out of the XJR than my old 3.0L X-Type, or the 3.2L Freelander...

 

it could also be journey length (or stop/start) or even use of the right foot.

 

Takes big ***** to drive a nice car with guage below E in New Orleans!

 

Thanks for reply.
I drive 70 miles a day; 30 highway miles and 5 city each direction. Always use cruise control. I drove car like I stole it for the first week but I got that out of my system.
My commute is ideal for good gas mileage. This jag currently doesn't get it.

 

It is likely to go up in the summer when the winter blend gas is gone and temperatures are higher. I always average three to five mpg better in the summer.

 

It just shows that if you can keep a ton-and-three-quarters at a constant speed and you're not burning gas bringing it back up to speed all the time ... then the only thing you are burning gas for is the energy lost in tyre flexing and in overcoming air resistance ... and the 350 does have a lovely low profile !

 

Hehe no doubt! Good thing my girlfriend wasn't paying attention. I did buy my car with a really really dark tint on the windows. Looks like a mobster car, people tend to think twice. Cops pull behind all the time to run my plates but have yet to get pulled over. Lol
Maybe I should put American flags on the hood and go for the diplomat look!

 

My XJR is black also. Only lightly tinted but they do have that look about them!