24 mpg for xk8, right or not?

[jonboy07]

cant seem to much better than 24.7 (mabie 25 mpg but not for long) no matter how light footed i am ( absolute bare min to maintain speed ) at 70, or even at 80-90 it stays about the same too, dont think this is right or do i under estimate the v8 lol, it seems like the left exhaust pipe somkes more than the right on tick over too, could be linked to my other post ref my theromstat, anybody any ideas? thanks

[G_T]

You might want to state your model year mate. 1996 was it?

I can't really comment on the car specifics (as I'm neither a mechanic nor an XK owner) but don't forget after 12 years of driving will have taken it's toll on mpg.

Also don't forget the following generics in terms of MPG; style of driving (urban/motorway/mixed), type of fuel used, time since last service, tyres, previous use of injector cleaner etc... These will all drastically effect your mpg (and mentioning them should help with a differential diagnosis).

Also don't forget that the people who tend to come up with MPG figures can be horrendously optimistic, for example I'm supposed to average 22mpg but the reality is I'm lucky to get 18mpg... I also find, and this is probably the same for all heavy V8s, that hammering the beast around the country lanes only yields marginally worse mpg than normal! I barely bother with the light-foot these days as a consequence.

I'm sure someone more knowledgable will be along to help further though.

Edited by G_T on Monday 8th December 00:11

[onlynik]

I've a 2003 XKR and get around 29/30 on the motorway.

Haven't checked todays run, but I's say that was a little low.

[Jaguar steve]

I hope you mean steam, not smoke from the exhaust. If it's smoke then MPG is the least of your worries. If it's steam then it's a indication thet the engine is not running at the correct temperature which will affect fuel consumption.

But 24MPG? That's not so bad.

Fit a new thermostat, make sure the brakes are not binding, put the tyre pressures up to the full load/high speed value and drive like a real pussy and you might, just might be able to nurse it up to 26 - 29 MPG on a steady long journey.

Preserving momentum and avoiding using the brakes is really important in a heavy car.

Edited by Jaguar steve on Monday 8th December 06:54

[Triple7]

If its the 4.0ltr/5spd, then thats about right. If its the 4.2ltr/6spd I would say closer to 30MPG.

[GavinPearson]

Triple7 said:

If its the 4.0ltr/5spd, then thats about right. If its the 4.2ltr/6spd I would say closer to 30MPG.

I agree. The car's a Grand Tourer, not an economy car.

[jonboy07]

ye it is the 96 4.0, has a full history, last 1 only 5.5k ogo(100k), i put injector treatment in about every 3 tankfulls, 24 mpg is what i get if i reset the comp and touch the throtle barely enough to maintain 70mph on the carrideway without breaking( really taking the piss ) ye i mean steam from the exhaust but still more from 1 than the other, quite noticable too, think it could be the lamda sensor? also do they change the plugs on the 100k service? wer'nt on the recipt for it, for £400 i think they should though, tried to check but some of the bolts were too rounded, so i suspect they never, could be that, ill have break out the mole grips( never good when you have to do that lol) thanks guys

[Triple7]

I would say 24MPG is average, but you shouldn't have to drive that gingerly.

[Jaguar steve]

Plugs are changed every 70k on the non supercharged engines.

On a cold and damp morning you will get a lot of steam from the exhausts until the engine has reached it's operating temperature and having a faulty thermostat will prolong the warm up period significantly and prevent the engine from achieving the correct temperature.

If the engine is not running at the right temperature it will almost certainly be over fuelling under certain load conditions and for a much longer time than usual due to the slow warm up so there's a good chance you'll see an improvement in fuel consumption - especially when it's been as cold as it has recently - when you replace the thermostat.

[jonboy07]

thanks for the help, isnt 70k a little long to be leaving plugs in?

[Jaguar steve]

The V8 is fitted with Platinum tipped plugs which do not errode like conventional electrodes and modern fuel and engine engine managmentgives a much cleaner burn so there's no problems with the plugs becomeing fouled either. I've changed a few sets of plugs on these engines at the recommended intervalls and beyond and never seen one in poor condition.

The only downside is the cost - up to £9.00 each unless you shop around.

I bought a set of 8 for my own car for less than a tenner the lot from e-bay. The seller was clearing out a job lot of old stock plugs he'd bought and hadn't a clue what they were or how much they retail for

[robocop]

jonboy, I have a '96 XK8 and have averaged about 20-21 over 4 years. That is mainly twisty A-roads of Wiltshire and having to kick-down past slower lorries etc. Drove up to see the folks in Chester this weekend and got 25mpg when I was not in a rush and in cruise mode with a lot more motorway.

So relax and enjoy the car, I reckon you are bang on with your figures

A couple of mpg makes no difference on a car like this, otherwise you would have bought a Matiz

Rgds
Simon

[pr100]

My 04 XK8 does 30mpg comfortably on a motorway run. It amuses me to set the computer readout to "Range" - most of my travelling is non-motorway and a range of say 150 miles can grow to 175 miles by the time I get back from a motorway run (without having added petrol).

Simon

[Shar2]

I've got a late '97 XK8 which even after a couple of re-maps still gives me 27-29 average on a motorway run and 22-24 on my drive to work, which is mostly stop-start at the moment, so your 24 is about right. Plugs should be changed every 60,000 miles on the older cars. Jaguar increased it to 70,000 after the first facelift models came out.

[NST]

not sure about the xk8, but my xkr 4.0 does 18-20mpg around town and mid - high 20s on the motorway.

mid 20s seems about right. i'd check the air filter and tyre pressures to see nothing is wrong. then give the car a good service.

[jonboy07]

thanks guys,never really had any prbs with 24 mpg, just heard from an other owner that he gets about 30 mpg and thought i was missing out lol, still i think ill loolk into going down the lpg route, mainly because i cant see any disadvantages with it except the initial price ofcourse lol, thanks

[Jasper Gilder]

I had an XK8 in 1997 and did 60,000 miles in it - worst fuel consumption of any Jag I've owned - it was hard to drag it over 22 MPG - I get more than that in the S type R around town!