I would like to put together a spreadsheet (yes I'm an engineer) of what mpg we're all getting. If your interested.
Now to give it some depth if you could tell me some simple details

Vert or coupe
4 or 4.2
8 or R
Primarily Highway, urban or mixed
UK or US gallons
Sporty or sedate driving style

I'll pull it all into a spreadsheet and we can see what the average actually is.
Pm me if you want to take part but remain anon, or post to the thread if you don't mind.

Sorry Jeff I haven't got a category for 600 hp monsters

 

I have a 4.2 XK8 coupe and with a mostly sedate driving style I am getting a combined MPG (UK) of 16.5.

The split between urban and highway miles is about 75% - 25%.

Highway driving I get 27-30mpg quite consistently (70-100 mph)

City only it was about 14mpg but city = London = really nasty traffic

 

Same here. My split is even more skewed towards urban driving (80% vs 20% for motorways) and so my mileage is 16mpg at best.

Best wishes, Colin

 

2001 Convertible.

I don't know if the other model years have the same feature, but on mine there is an option to see average speed, along with mpg and so forth. Average speed may give a good snapshot of city vs. highway miles.

My average speed is 38 mph and average mpg is 19.4. I drive fairly moderately as a rule, but do drive faster than most other people on the highway. I typically don't accelerate very hard, which is the big gas burner.

 

Mine is an '01 vert. I checked the "B" side of the trip computer and came up with the following:

4171 total miles (since last reset)
228.7 US gallons used
18.1 average MPG
27 MPH average speed

As you can tell by the speed, mine is mostly urban driving. Guessing, I would say it's an 80/20 split, urban to highway.

I took a 600+ mile trip last year and averaged 27 MPG for mostly highway driving at 75-80 MPH.

 

I might add for your data that before a couple of fairly long highway drives of about 150 miles each a few months ago, my average mph was 35 and mpg was 18.6.

 

Mine presently reads 35 mph average and 19.5 miles to the gallon. The trip earlier this month to the mountains 27.5 per gallon on the Interstate, refilled and it averaged 22 miles per at an average speed of 47 mph on the return trip of back country roads. Jim

 

My XK8 4.0 usually averages about 19mpg ( UK Gallons ) for daily driving, and has been as good as 28mpg on an interstate trip using the Freeway for most of the journey.

 

Vert or coupe
4 or 4.2
8 or R
Primarily Highway, urban or mixed
UK or US gallons
Sporty or sedate driving style

Over the last 1500 miles = 17.6mpg. Over the last two years = 17.2 - 17.9mpg. I reset the "B side" of my gauges about every 10th fill up.

I only use 100% gas (no ethanol blends) unless I cannot find it.

Although my driving is "mixed" between urban and highway, I have a VERY heavy foot and drive Cough-Cough... "sporty" two or three times a week for 30-40 miles at a time on the hilly back roads of Missouri. I ALWAYS drive in "sport" mode and shift that turd of a transmission (6HP26) manually 100% of the time. (Unless that friggin "blinking D" on the J-gate wont let me!)

In the last 2+ years, excepting when the car was being worked on in my shop or there was snow on the roads, not a week has gone by that my coupe hasn't seen the far side of 100mph at least once, usually several times.

I am very pleased with the fuel milage to fun ratio my "R" provides.

 

At a 100 MPH you are getting 27-30 MPG?

With cruise set to 75 MPH, I get 24-25 MPG and that is in Florida were the roads are really pretty flat.

In Alabama I average about 21-22 MPG on hilly roads w/cruise set at 75.

 

2006 XK8 4.2 Victory Edition Convertible pushing 62,000 miles....

Probably very close to a 60/40 highway/city mix....

Always gets premium fuel (U.S. gallons)....

It's my wife's car. She's probably never driven faster than 85 mph in her life, and only then to get around the occasional lane blocker on the highway....

The only time I ever check the mpg is after her 1,500-mile solo round trips to Tampa and back, six or seven times per year. For these trips the car is stuffed with her 147 bags of clothing and shoes, runs the HVAC full-time to maintain 70 degrees in the cabin regardless of the weather outside, and essentially does the trip with cruise control set at 72 to 77 mph depending upon what the various State Troopers appear to be allowing on I-95. She consistently averages 28 mpg on these trips, winter or summer. I always thought the winter trips would be slightly more efficient with the colder air temps, but that has not proven to be the case thus far....

I rarely drive the car because I'm far too tall to fit in it, but I guarantee you my mpg would be much worse than hers....

 

I don't get 27-30mpg at 100mph. I get 27-30mpg driving between 70-100mph, usually closer to 70 as this is the speed limit in the UK
However I will push it to 100 perhaps for 20-25% of my highway trips.

I have never gone below 27mpg.

 

'97 ragtop 4.0: 8.5 Km on a litre. Drive slowly 95% of the time, very bad boy at traffic lights, roundabouts and occasionally 'cleaning the pipes' at 150% the legal speed...

 

Looks like I'm right in line with the rest of you:

Vert or coupe - 2001 Convertible
4 or 4.2 - 4
8 or R - 8
Primarily Highway, urban or mixed - 70/30
UK or US gallons - US
Sporty or sedate driving style - mostly sedate, plus some driving with "purpose"

I probably average 18-19 mpg overall. I've not taken any long trips, but one 100 miler through the mountains got me around 23mpg.

 

Coupe
4.2
R
Mixed (70/30 urban)
US gallons
Sport-ish

Around 18-19 overall. On a long trip 28-29 is easily repeatable at 85mph.

One thing to keep in mind is that the 4.2 has an extra gear, which helps.

 

Howdy Folks:
FWIW, When I compared my trip computer's MPG readings to my GPS Miles Traveled /Fillup Gallons Pumped calculations for refueling intervals on my 2000+ mile road trip last fall, the correction factor was about 1.1
Thus, for example, 21 MPG on the display coresponded to a calculated 23.1 MPG. Regardless, I just enjoy the drive and as of yet, I do not sweat the gas cost.
(I have std size tires)

 

2001 xkr 55k

avg 13.4mpg 60/40 split

avg 20mpg on cuise control at 75mph

US gallons

bit of a lead foot as my tires last 15Kmiles at best

 

2004 XK8 Convertible, 4.2 100,000 miles Premium fuel always

Stricltly City (short trips) 18.5 Top down
City mixed with local Freeway 21 Top down
Interstate at 80+ mph 26.5 Top up (no topless trips yet!)

Almost all of my driving is done with the a/c on, even with the top down! (Hey! It's HOT here!)

 

XKR 4.2 Convertible 100k
50/50 Urban/Freeway
Average: 20.5 MpUSG
Highest MPG recorded (100 mile cruise at ~60mph): 31.4 MpUSG
Lowest MPG Recorded (50 miles at ~125mph): 11.8 MpUSG

Cannot say I notice much difference with top up or down. 125mph with top down perhaps gets a bit noisy.

 

Thanks all so far.
The results look like this