Arrived in Brisbane for surprise visit for son's birthday in my XKR (2000). Just short of 2000 klms. Split into two legs of 1200 and 800 which we covered with ease at a fuel return of 11.6 litres per 100 km.
These cars just eat up the miles and but for big brothers average speed monitoring systems along the highways it could be done even quicker.
Ambient temperatures for a good part of the distance was in the 40's (celcius) but not a hint of trouble from the car.

 

11.6 litres / 100 km = 24 MPG (British) which is a very good figure for a supercharged V8. Did you make a note of the average speed the trip computer recorded?

 

Yes, that shows as 93 kph. The speed limit for large part was 100 or 110 kph which were mostly observed and l did take note of a slightly better fuel return at the higher speed. This may have been real or imagined but earlier in the trip the limit was more 100 kph and fuel use tended to be closer to 12 litres per 100 with this dropping slightly after more miles at 110 kph limit.

 

So about 58mph. Most of my driving is around town and on minor roads, so my average speed and MPG is a lot less.

 

Going to trying some of that eating miles thing myself today. Driving a little over 950 miles, in 2 legs (from NE Oklahoma to Austin, Texas RT). Weather is hovering at 35- 40 degrees F, very cloudy with a good chance of rain somewhere along the way. And very windy, a steady 15 mph and gusting to 30 mph.

We'll see how well those new BFG Comp 2 A/S tires hold the road.

 

Last summer , on long drives I was consistently getting about 9.5 L / 100 km (30 mpg) at 115 kph (70 mph) ambient temps in the mid 20s ( 75-80 F) In absolute comfort.........I am VERY pleased

 

Same as our SAAB 9-5 2.3 Aero

 

 

 

Very nice numbers.

I've put almost 120,000 miles on Kitty, keeping good fuel data all along. For all types of driving she's averaged 48 MPH and 23 MPG. I've also had a few long highway runs (70+ MPH) at 29(+/-) MPG!

You are sooo,... correct: the miles just disappear beneath the cowl. :-)

 

Both of my cars are 4.0L SC engines with W5A580/722.6 5 speed gearboxes. The best I've ever gotten highway is 21mpg, with average driving netting mid teens in your average back roads. That's the smaller gallon, not the imperial one.

This winter in Michigan, with warming up and not necessarily driving easy, my XJR has been getting about 12mpg. It normally averages 16.

 

Hi 80's! In my record keeping I've also kept an eye on summer vs. winter performance. As I suspected, the car gets significantly better MPGs in the warmer months. One obvious reason is that the enrichment cycle last longer when the engine is cold, and of course the more morning/cold starts you have per miles driven the more influence that factor will have. I guess it's also possible that the denser air will increase drag (sorry - I'm also an Aerospace Engineer - lol). Both of these would certainly be exacerbated in Michigan vs. Maryland.

In addition to my daily commute of about 20 miles (RT), I drive many thousands of highway miles a year with a normal cruising speed of 80 / Speed Limit+10. I also maintain my tire pressures between 40 & 45 PSI. With over 200K miles on Kitty, I don't drive her aggressively very often (but do "enjoy" her a bit from time to time . I would say that my commuting MPGs are around 18 with an average speed around 24. Having the extra gear in my transmission would obviously help, but I don't know what the actual numbers are. I've taken great care to reduce intake air leaks, keep the FTs as low as I can, and let the engine run as optimally as possible. Shell gasoline does seem to get better MPGs than lower priced 93 octane fuels, but I'm still researching that. And I put an ounce or two of MMO in each tank full. Oh, yeh - this is actually the second engine the car has had. This one "only" has about 150K miles on it (assuming everyone was telling me the truth).