I'm thinking about "upgrading" to a 2004-06 XJ8 primarily for the increased gas mileage. I have an 03 XJ8 that gets in the low 20's on the highway and was wondering if those of you with the newer model get significantly better MPG?

I filled up yesterday, it cost me $76.76 -- an all-time high!

 

You can convert this to mpg but for my 04 XJR

Running average is 13.2 L/100km
I never reset the trip B so i have an overall average

That a little higher than normal as as I had a plug/coill failure recently

Short term averages over 1-2 tanks
Bumper to bumper traffic 13.5 L/100km
Normal city peak hour traffic 12.1 L/100km
City traffic (not peak hour) 10.6 L/100km
Freeway @ 110 kph, 9.1 L/100km
Intercity highway @ 120kph, 8.6 L/100km

On a side not I have the adaptive cruise control and use that a lot even in city traffic.
Best guess im using the cruise control 80% of my driving time

Depending on your thought that helps or harms the fuel use. Personally I dont care and use it to make the driving more pleasant. In the same way the a/c is always on. Not going to be uncomfortable to save a bit of fuel.
It always amazes me how may people are in bumper to bumper traffic with the windows down and a/c off. Guess I'd rather not arrive stinky and with an extra cent in my pocket

Cheers
34by151

 

05 Vdp.
28.5 mpg (us) at 70 mph.
24.5 avg city/highway over 3000 mile period.
Winter gas and 10% ethanol.

 

I have had mine for just over a year now and have averaged over all 32 MPG (Imperial gallons) This would be for a mixed driving of both highway and town driving.

On the initial trip up from North Carolina from where I purchased the car through the Canadian border to Toronto. I averaged 34.2 MPG (again Imperial Gallons) with an averaged speed of 70 MPH. My car is an 2005 XJ8L VDP.

 

What technical differences are there between 2003 and 2004-2006 that would yield better fuel consumption?

 

For one, all aluminum body.

 

Weight.

 

My long term trip on "A" is running around 24 mpg (English gallon). Holiday to Germany (twice) gave over 28 mpg. This car seems to give more mpg the faster you go !!

 

More advanced engine. 2003 XJ8 had the AJ26 engine and the 2004 was upgraded to the AJ33. The newer engine is more fuel efficient with more power. Couple this together with the lighter aluminum body that somebody else has mentioned already and the six speed gearbox and you get the results as has been reported.

 

The technical improvements yield better power and fuel efficiency.

 

I got 29.5mpg on my last week's trip to Palm Desert (220mi).
I found out the key to best mpg is to use cruise control wherever possible!

Cheers,
Wolfy

 

05 VDP
28-29 mpg hwy at 70-75mph (over 30 if I keep it between 60 and 65, but that just seems wrong )

Avg 25-26 (I use the car mostly for hwy/work commute)

 

I avg 22.2 mpg if you fancy a S/C figure. Highway mileage is still really good - 27 ish.

 

If I had a super v8, I might not even notice my gas mileage! LOL Nice car!

 

According to my X350 Technical Notes the Cruise Control has additional software to minimise fuel consumption.

 

Thanks Mike, the used market has a lot of xjrs and superv8s available.

 

Ok, lots of good information here already, its lighter body, a better engine with better fuel management equaling better fuel economy and a 6 speed gear box.
That being said my XJR gets 15 in the city and up to 30 on the highway, driving it lightly. If pressed for time, it drops down to 13 in the city and 26 on the highway. And thats almost pedal to the metal

 

On a recent trip, I snapped the following pics after a period of time on highway. Super V8.

Please see pics.

 

Connecticut seems to be notorious for having the worst gasoline formulation in the northeast, and I just got 18.8 mpg for my first tank. It was mostly back roads, in town, and some highway.

I think I saw 17 in town and 21 highway as a spec somewhere, but I'm not sure. My foot is not especially heavy, either.

Locals swear that if they buy their gasoline in Massachusetts, they get better mileage than if they buy it here. This has allegedly been confirmed by oil company employees, supposedly some nonsense about what the state requires, and we have 10% EtOH in ours.

It doesn't surprise me at all.

 

I average 22 mpg on my 2004 XJR. mostly highway driving. The highest I have ever achieved is .