Changing XJ from diesel to petrol

[OGR4M]

Evening all,

I have a 2011 XJ luxury (read as, poverty spec) 3.0 diesel, got it at a good price with relatively low miles, it’s my first jaaag and I’ve completely fallen for it.

Now, I would never accuse my car of being slow - the grunt of diesel torque is actually quite addictive when I get the gears right - but with the clamping down on diesel, and the potential costs of them going wrong (see the thread on here from jag lumps failing), the upgrade to proper fuel, and some extra bhp (and a supercharger) gets very tempting indeed.

I travel a shade over 60 miles per day, and according to my handy app, I’ve so far averaged a lifetime 39mpg over 14k miles. Anyone here, who has experience of the petrol lumps, in any of their applications; xj, xk, f type etc, could you give advice/experience on the running costs of a petrol?

Obviously I would be due a huge hit on mpg, my guess on my commute, which is very fuel-friendly, would be ~30mpg with the v6, and up to ~25mpg with the v8.

TL:DR, want a petrol, diesel is rubbish, is it going to bankrupt me?

Thanks all!

P.S, if the 8-speed unit, and/or the more powerful diesel in the facelift models, improves things (not just mpg, but the driving experience also) then by all means lemme know!

[psi310398]

I suspect you already know the answers to your questions! Not quite if you need to ask, you can't afford it but not far off.

I had the use of the 5 litre supercharged 500-odd hp XJ recently. Lovely fast car and all that, although about the size of Margate. It was on loan so I behaved myself but I'd say that if you go petrol (esp supercharged) and you like the loud pedal, you should be investing not only in a Shell loyalty card, but their shares as well.

You'll be lucky in real world driving to get better than 18-20 mpg out of it. Can't help on residuals/servicing costs/reliabilty I'm afraid, although my experience of earlier Jags (which might be based on the reputation of the previous manufacturers) would suggest that none is in the Porsche league.

[BenjiS]

I've had a 3l supercharged XF for the last year. The 380bhp version.

It's done around 25mpg in mixed driving (but mostly urban) over 7000 miles. On a motorway run it'll return 34ish. I reckon you'd get low 20s from the 3l petrol XJ, as it's lower power at 335bhp.

Not many around though.

[Shirt587]

5 litre non-supercharged XK, 22mpg long term average with lots of urban stuff.
Would go up to 27-28 on long motorway runs through average speed camera zones...

[V88Dicky]

I've used the wife's car for work a few times, and like you, it's an mpg friendly commute (especially at 0530 each day), being 28 miles mostly made up of quiet dual carriageway.

It's not an XJ, but the XF 5.0, so a bit heavier due to all steel construction. It managed 27.5mpg for the week, with the 6 speed ZF. On longer runs it breaks into the 30's quite easily.

HTH

[OGR4M]

Shirt587 said:

5 litre non-supercharged XK, 22mpg long term average with lots of urban stuff.
Would go up to 27-28 on long motorway runs through average speed camera zones...

If I didn’t need back seats, an XK, possibly the R, would be one of the favourites. But I need a child seat and I’m reliably informed that the rear seats are merely a well-finished parcel shelf...

V88Dicky said:

I've used the wife's car for work a few times, and like you, it's an mpg friendly commute (especially at 0530 each day), being 28 miles mostly made up of quiet dual carriageway.

It's not an XJ, but the XF 5.0, so a bit heavier due to all steel construction. It managed 27.5mpg for the week, with the 6 speed ZF. On longer runs it breaks into the 30's quite easily.

HTH

I don’t know whether the XJR has any ZF6 variants, but if I got a supersport then it probably would be.

27mpg is perfectly acceptable in the long run, I watched a YouTube vid of Harry Metcalfe, his XJR managed 38mpg on a cruise through France! Unachievable on a normal commute of course - but I do go on long runs occasionally.

Now, anyone want to lend me a few quid?

[fatboy b]

I bought an XFR-S after a couple of XFS 3.0Ds. Love it. I only look at the mpg to check nothing is wrong as doing that helped spot a leaking fuel filter in an Audi A4 a few years back. The last tank averaged 19.4. But that’s lots of short hooning journeys and cold starts. If I go to the office - about 60 miles each way, I get high 20’s. Other long journeys on the motorway in rush hour traffic has seen 34 - but that’s rare. Generally it sees 23-25. I’m also doing 22k a year.

[cableguy]

Had my 2010 XJ 5.0 Portfolio for nearly three years now, the last two have been town and short dual carriageway journeys and the car consistently does 400miles to a tank (£75.00).

The motor is a peach and IIRC when Evo Magazine tested it, the 5.0V8 was the pick of the bunch re power, weight dist. etc. It's a fast car when pushing on but ultra refined when wafting around.
I normally keep daily drivers for 18-24months max but i'm struggling with what to replace the car with, although it will sold very soon as I have a couple of classics that I need to use more.

C.

[OGR4M]

Thanks for all the info, chaps - is a decent length test drive available? When I last went to a dealer and test drove an XF they let me drive up to 70(ish) on the a5, round a roundabout and back. I’m not expecting to keep one for the weekend, but would it be able to have one for most of a day, or at least enough to time explore it round town, plus commute-type scenarios?

Probably best to mention I will have to wait until the right car comes up, the cheapest XJRs are getting close to my budget now, but they all seem to be white, which is not my bag..

[Shirt587]

OGR4M said:

If I didn’t need back seats, an XK, possibly the R, would be one of the favourites. But I need a child seat and I’m reliably informed that the rear seats are merely a well-finished parcel shelf...

They're perfectly sized for carrier bags.

[a8hex]

OGR4M said:

If I didn’t need back seats, an XK, possibly the R, would be one of the favourites. But I need a child seat and I’m reliably informed that the rear seats are merely a well-finished parcel shelf...

Having said that my kids who'd spent years complaining that there wasn't as much room in the back of my XJ6 (X300) as there was in LadyB8's E-Class happily climbed into the back of the XKR and swore blind that there was plenty of space thank you. Mind, after I'd bought it I've never had both in the back at the same time.

[OGR4M]

a8hex said:

Having said that my kids who'd spent years complaining that there wasn't as much room in the back of my XJ6 (X300) as there was in LadyB8's E-Class happily climbed into the back of the XKR and swore blind that there was plenty of space thank you. Mind, after I'd bought it I've never had both in the back at the same time.

From what I’ve read/seen, my issue comes from the requirement for a big child seat - mini OGR4M is 5, and obviously will require a sizeable kiddy chair until she’s however tall the regs say - the bucketed nature of the XKR rear seats would prevent the child seat from fitting correctly.

Ah, just pad the bucket of the seat with a firm cushion or similar, the plonk the sprog on top of that, you say - headroom then becomes the issue, apparently.

Which is all a shame, as a 2012/2013 XKR seems to come in a shade cheaper than an XJR of the same age, with all the same techy gubbins (more or less).

[soprano]

XFR here with the ZF6 box. 20.7 mpg average, quite a lot of motorway driving but pretty heavy right foot.

The day I picked it up, I averaged 9.9mpg. I was being ‘enthusiastic’.

[OGR4M]

soprano said:

The day I picked it up, I averaged 9.9mpg. I was being ‘enthusiastic’.

This is what would stop me buying a petrol - an experiement I did recently, on a closed section of road using trained professionals, I compared my usual commute mpg of ~45mpg vs what I could get it down to, and after checking the speed limiter functions correctly I got the diesel down to 31mpg after 30 miles of dual carriageway and A-roads.

20mpg is an eye-watering concept for me, as my 39mpg lifetime average means I’m spending ~£200 per month on burning heavy oil, double that cost and the “diesels are rubbish” argument starts thinning out a tad..

Do I drive the petrols, or is that a bad idea for my bank balance?

[V88Dicky]

As a slight aside, petrol (at least in my neck of the woods) is currently 2 - 5 pence per litre cheaper than the black stuff, so don't forget to factor that into your equations.
I guarantee you one thing though, once you drive a Jag V8, you'll not want to go back to diesel, so be careful!

Yes, of course it'll cost you a bit more, that's a given. But, if you're careful on your commute, and try to separate it from 'spirited' driving, i.e. you're just driving for enjoyment, then you can make it work.

It all boils down to whether you really want one, or not?

[yajeed]

OGR4M said:

Evening all,

I have a 2011 XJ luxury (read as, poverty spec) 3.0 diesel, got it at a good price with relatively low miles, it’s my first jaaag and I’ve completely fallen for it.

Now, I would never accuse my car of being slow - the grunt of diesel torque is actually quite addictive when I get the gears right - but with the clamping down on diesel, and the potential costs of them going wrong (see the thread on here from jag lumps failing), the upgrade to proper fuel, and some extra bhp (and a supercharger) gets very tempting indeed.

I travel a shade over 60 miles per day, and according to my handy app, I’ve so far averaged a lifetime 39mpg over 14k miles. Anyone here, who has experience of the petrol lumps, in any of their applications; xj, xk, f type etc, could you give advice/experience on the running costs of a petrol?

Obviously I would be due a huge hit on mpg, my guess on my commute, which is very fuel-friendly, would be ~30mpg with the v6, and up to ~25mpg with the v8.

TL:DR, want a petrol, diesel is rubbish, is it going to bankrupt me?

Thanks all!

P.S, if the 8-speed unit, and/or the more powerful diesel in the facelift models, improves things (not just mpg, but the driving experience also) then by all means lemme know!

8 speed and a later chipped diesel 3.0 XJ. 320 bhp on the dyno and averaging 45mpg, but get well over 50 on the motorway (60 when I'm wafting around in no hurry).

[Simpo Two]

OGR4M said:

I travel a shade over 60 miles per day, and according to my handy app, I’ve so far averaged a lifetime 39mpg over 14k miles. Anyone here, who has experience of the petrol lumps, in any of their applications; xj, xk, f type etc, could you give advice/experience on the running costs of a petrol?

I changed from an XF 3.0D to XK 4.2. The XF averaged about 37mpg, the XK about 28. I can't immediately work out how much more that costs but on an annual mileage of about 10K it's not noticeable in the big scheme of things. I didn't change cars to change fuel; if there was a twin turbo XK-D I'd be happy to drive one but the option doesn't exist. I think I prefer the power curve of a turbo-diesel.

Assuming cost is a factor for you, then the petrol v diesel debate changes the more miles you do. How much extra are you prepared to pay for a petrol engine, and what advantages will you enjoy for that extra?