2000 XK8 Convertible 4.0 - l drive rather aggresively - 90% highway - 28MPG on the A (reset every fill up); recent trip of 50/50 showed 20.1mpg. quite happy with the mpg in the jag as previous beast was a 3.5l H/O V6 Dodge Magnum that barely got 17mpg

 

1999 Jaguar XK8 w/122000 miles (multi daily driver ).


Since last reset:

• Trip A: 2523 MLS
• Ave Fuel: 20.7 MPG
• Ave Speed: 29 MPH
• City/Freeway: 80%/20%

Always running on Shell V Power for what it's worth.
Thanks for this great project!
Danny.

 

16.8 for 1568 miles. 50/50 Hwy/town. Lots of winter-idling and car warming up in garage on that though. 21 MPH avg. I don't floor it off the line but do often after I get into 2nd gear at stop lights and on-ramps.

Taking the car home I got 26.8 for 454 miles. Literally all highway. Left the gas station and onto hwy for all of those.

 

I drive somewhat aggressively. I usually get 13 mpg city and about 17 mpg highway out of my XKR. If I really try to drive for economy, I get about 20 city, 27 highway.

 

2000 XK8 95% city 5% highway. I average about 17 US MPG city and 20 highway.

 

Lucky lucky lucky!

For me, it must be driving in Mt. P alot, as my Avg. Speed between fill-ups and trip A resets is always 25 mph. I tend to take it easy lately to see if I have an issue going on.

16.0 30% highway 70% town

Long term average (Trip B w/ ~1200 miles) is 15.8

4.0 R Coupe US Gallons moderate driving style

 

Bit of an update. 2003 XKR, 4.2L coupe

I just did 950 miles, 95% highway at 78-85 mph in decent weather, cool air temps and about 2/3 of the driving was done with pure gasoline (not alcohol blends.)

22.3 mpg for the entire distance.

There was one 145 mph blast - in order to show a Nissan 350Z (came up aside me at at least 95 mph) that unless I allowed him to do so, he wasn't getting his bumper in front of mine. Yeah, kind of a "dick" move but I just wanted to know where our cars rated against a Jap "techno GT."

His wife (and mine) were visibly irritated....

Yeah... So.....

 

one of my lads has got a 350, swears it's quicker than my R, I'll inform him of your "experiment" lol

 

Updated Results.
In short it looks like the 4.2 really is a more economical beast than the 4.0

The 4.0R appears to be a very thirsty beast dropping almost 7mpg from a 4.2 in the Supercharged form and 6 mpg in the NA form.

The cost of the 7mpg just to make you all feel better equates to approx £100 per 1,000 miles based on UK fuel prices.

For me, based on 22,000 miles/year this is £2,200 per year cost increase in fuel running my 4.0R rather than a 4.2R, I can feel another upgrade coming on.

But the maths says it will save us money dear

 

Perhaps I am reading this chart improperly, but it looks to me like you have the XK8 4.2 Coupe getting 19.75 average MPG, while the vert gets 26.5. Now, assuming the lighter weight and also I would assume a more aerodynamic vehicle with the coupe (especially with top down on the vert) I think that that is a rather startling anomaly.

I think that you got some interesting numbers here, but I wonder if the sample size and the accuracy of the reports allow much of a real conclusion.

Now, I don't doubt that the 4.2 may get a little better mileage with the additional gear and the fact that those you reported on are newer and probably in better tune, but I am wondering if there is really a 6 and 7 mpg difference.

Be that as it may, thanks for putting this together, it was an interesting exercise.

 

The numbers are a little limited, and the 4.2 coupe results are scewed by the urban 16.2 results.

The more data we put in the table the more accurate it will get.

Thanks

 

Last Sunday we finally had some good weather but still a little windy.but I decided to take a short run to check out the XK8. I'd like to take it on a longer run this summer and want to make sure everything is working right.
Anyway this run was for 398 miles and consisted of city (35-40mph), 2 lane country (60-65 mph) and interstate (75mph) fuel use was 15.3 US gallons for average of 26.0 mpg.
This is the second trip in the last year of around 400 miles that we've made with out having to stop for fuel. The first trip was all interstate and came out to 25 mpg.

 

So many things that influence the mpg as Green Machine also mentioned.

But I would also like to give some for a 600hp+ 4.0 car.

Just done an agonizing measurement, 4 long trips of about 80 miles, with 4 short 10 mile trips, and I have tried here to drive economical and close to the max speeds allowed.

That gave me an average of 20.5 mpg (US).

When I drive normal, so using the power (what some may find aggressive fast/fun driving) with 80% Highway and 20% City over a couple of thousand miles gives an average of 16 mpg.

 

So what do you get in city driving? 13 mpg?

 

I guess my car would be comparable to a stock setup (especially for city driving), so if you get what you are saying (17mpg) I would probably get the same for economical driving (or driving with xk8 power levels).

 

Your 4.0l 600hp delivers far better MPG than my stock 4.0R

Maybe the stock 4.0l setup runs quite rich?
I have noticed that even on light acceleration my instant MPG drops to 8-9 whereas in the none SC coupe I had it would only drop that low if I was on full throttle, mild acceleration would dip to 15-16 mpg.

Overfuel to reduce the combustion temperature increase from the SC?
but on the overcharged engine there is more air so you get more burn and more power out of the same volume of fuel = more efficiency but maybe the combustion temps rise increasing the emissions??

 

I reported the mileage that my car indicates on the speedo.

It seems to me that a lot of others are reporting actual mileage for specific drives by the old fashioned way of calculating mileage vs gallons used.

I haven't made a comparison in my Jag, since I don't drive it much, but on my other vehicle I have and it basically comes back that I actually get about 2 mpg more than what the speedo says that I am getting.

I wonder how much of a disparity, if any, that there is in our Jags between what our car tells us, and what we get when we actually check it.

I am going to check mine the old fashioned way next time to see.

 

Answers for my 2006 XK8 with 23,800 total miles:
Vert., 4.2, XK8, urban (small town) US sedate.
Over the last 2800 miles my ave. is 15 miles per gallon.
Over the last 200 miles my average is 17 miles per gallon.
17 is more typical, and please use that number.

I'm glad you're doing this, as I was concearned about my low miles per gallon. I am curious about other low millage cars? Should be better fuel economy, excluding rebuild engine cars. Mine was owned by a blue-haired lady in Carmel, CA. She averaged 3,500 miles per year.

 

'99 vert., 4.0 N/A, 80,000mi. 23mph ave (exciting life,eh?) 99% urban, 20.5 mpg.

 

I've found on our '97 XK8 coupe that what the computer is saying and then what I calculate at fill up is pretty much the same. Also when I compare the speedo with my GPS the speedo is exactly the same.