Is there some sort of aftermarket "flash" that can ease the transmission a little as a "new" choice. One of the guys I work with has a Merc S550 and he has several settings that are something like: 1) Sport, 2) Comfort, 3) Economy. The S550 is a completely different car from the XK, but our "choices" are limited to: 1) Sport and 2) Even More Sport. It would be nice to have a "Cruise/Comfort" and an "Economy" set of settings in addition to "Sport" and "Even More Sport".

While I rarely take my XK on congested highways, when I do, it would be nice to have an economy setting so that my acceleration from 3 MPH to 15 MPH and back to 3 MPH every 50 feet wasn't accompanied by big thirsty growl and throatful of gas.

My XK and XJ both have the same engine (normally aspirated 4.2L) but the XJ gets MUCH, MUCH better miles per gallon. The XJ typically gets 20 to 21 miles per gallon in mixed driving and as much as 30 on the open road. The XK gets 15 "around town" and maybe 24 to 25 on the open road. I haven't bothered checking gas usage against miles to see of the car computer calculations are accurate, but based on how often I have to fill the car, I would guess that the 15 MPH average is being very generous.

I thought this incongruous in part because the XK is 12" shorter and at least a couple hundred lbs lighter.

 

From my phone app I can't see what year your XK is, but at some point they introduced the winter mode which severely tames the gear ratio and throttle response. I use it around town as I frequently drive in heavy traffic and rainy conditions, but I've never tested the gas mileage. You've given me a project to work on! Anyway, it's the third "comfort/cruise" setting you seek.

 

I just press the pedal lightly. No roar. Press harder - roar.

 

The XKR has similar modes as the Merc. From most economical to performance: Snow, D, D with Dynamic Mode, S and S with Dynamic Mode. Snow is keeps the revs down with no quick gear changes. S and Dynamic with the pedal shifters engaged puts the car into a completely different performance level (suspension tightens up, dynamics become much more performance turned, high revs can be maintained, shifting is very quick).

 

Tyre brand can reallymake a difference on gas mileage : eg Handkook Ventus V12's lowered my '07 XK gas mileage about 1.5 -2.0 mpg! This is compared to Dunlops but the ride is so much smoother.

Cheers, Adrian

 

My '08 XK would get very close to 30 MPG in all freeway driving. My multi-thousands miles average with mostly highway driving was around 25 MPG.

Not sure why you find it that you need a throatful of gas for slight acceleration. My car would simply just roll on and off at low speeds with hardly any sounds from the engine. The only time I required more was when I installed a free-flow catback exhaust that basically killed the low RPM power and torque for the 4.2 engine. I went back to stock after that.

 

A couple things in regard to the transmission settings, mileage and acceleration. In our stop-and-go traffic, there seems to be no pattern, in some sections cars will accelerate quickly and then slow down quickly, at other times, you get to accelerate and sustain it for a decent distance. When I accelerate slowly and try to keep a more steady pace, I get better mileage but often will get nasty honks from the impatient behind me. If the traffic is moving slowly and you can accelerate slowly, there's no throatful of gas, but when it's a quick pattern of stop and go...more gas is used.

The low end torque on the XK is much more than on the XJ (logical and something you'd expect). It seems to stay in gear longer too, and is somewhat similar to the "sport" setting on the XJ if I had to guess. The sport setting on the XK seems to hold it a bit longer again.

It would be nice to have an "economy" setting on the XK that was similar to the "normal" setting on the XJ and then have a couple sport settings also (to exercise the cat when she needs it).

I have an '07 so I don't have "winter" mode. I wonder if there's a transmission software update that would allow the addition of a "winter" mode on the '07.

I have Michelins which, I believe, are supposed to provide pretty good mileage. I haven't tried anything else and the Michelins are fairly new.

 

I drove downtown today in moderate traffic on the freeway that didn't require stop and go, but did keep the average speed around 55 to 60 and got 32 MPG. Pretty good. But once I got downtown into lights and other slowness, it dropped back quickly. There was a great exhibition downtown at the National Gallery of Art of photographs by a Captain Tripe done in 1858-1860 in India.