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Jaguar XJ6/12

Jaguar XJ6/12 Published: 2nd Sep 2015 - 0 Comments - Be the first, contribute now!

Jaguar XJ6/12

Fast Facts

  • Best model: Series I 4.2 manual
  • Worst model: Series II 3.4 auto
  • Budget buy: Series II 3.4
  • OK for unleaded?: Yes – but use superunleaded
  • Will it fit in the garage? (mm): 4816 x 1772mm
  • Spares situation: Good except S1 front wings and grilles
  • DIY ease?: Generally good
  • Club support: Excellent
  • Appreciating asset?: Yes, especially the coupés
  • Good buy or good-bye?: After years of being out in the cold, the Coventry cat is finally being appreciated for being the great car that it is
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Jaguar’s legendary saloon is in another league, compared to the Mk2 it replaced, yet prices remain at bargain levels. Series II much derided but offers worthwhile improvements over the original, if you find a good one. XJ12 even better but running costs are much higher. An all time great...


There’s something special about having a V12 in your classic; let’s face it, not many cars have ever come so equipped. While most classics packing a V12 cost well into five figures, buy a Jaguar XJ and you needn’t spend any more than £5000; if you can afford the fuel, this is a true classic bargain. However, if you can’t afford the fuel costs, there’s always the XJ6 to consider, which is almost as smooth, plenty fast enough and easier on the wallet.

Good enough to be crowned Car of the Year in 1969, the XJ6 marked the start of a new era for Jaguar, but the company’s cars have always represented great value. During more than two decades of production, there were three series of XJs, available with a choice of wheelbases, transmissions and engines – and for the Series 2 there was also briefly the option of a great-looking coupé too. Just working out which is the best one for you can be a challenge; here we guide you through the first two series, before the heavily revised final iteration, introduced in 1979.


1968 That October, the XJ6 replaces the S-Type, 420, 420G and Mk2 although the 420 and 420G saloons remained in service for a few more years. While this new one-model policy could have decimated Jaguar’s sales, it did the opposite, the new car instantly making its predecessors look very dated and all for under £1800. Despite this, much was carried over, including the XK six-cylinder engines (albeit in a new short stroke 2.8-litre guise), the rear suspension and the transmissions with overdrive optional. 1969 The slightly more upmarket Daimler Sovereign goes on sale. It’s identical to the Jaguar XJ6 in almost every way apart from the badging.

1972 At long last the V12 engine first seen in the S3 E-type is offered in the XJ12 and Daimler Double Six, along with the new flagship air conditioned LWB Vanden Plas Double Six. From this point on there are also improved pistons with two valve recesses fitted to the iffy 180bhp 2.8 to increase its reliability where burnt pistons were the order of the day. LWB option is introduced across all XJ6 models for ’73.
1973 Production of the short-wheelbase models cease due to lack of demand. Jaguar shows off its revised SII range.

1974 The Series II replaces the original after more than 98,000 sales of the latter had been produced. The redesigned bodyshell now features side impact protection, new multi-pin plug connections for the wiring loom and there’s also a much-improved heating and air conditioning system. The arrival of the Series II brings with it a new bodystyle; a stylish coupé called the XJC although it’s not showroom ready until 1975. In this year, the final 2.8-litre cars are built.

1975 New arrivals include the XJ6 3.4 (in place of the by-now defunct 2.8-litre XJ6) and Daimler Vanden Plas 4.2. All V12s now have fuel injection, while all XJ12 saloons gain a vinyl roof as standard. The 3.4 engine isn’t a return of the classic XK unit but instead an adaption of the 4.2 although, derated to 167bhp.

1977 XJ12s now feature a superior GM400 automatic transmission and the final coupés are built after 8300 sales. 1978 Fuel injection is now fitted to the 4.2-litre XJ6 – but only US market cars get it. UK buyers still have carb-fed engines until introduction of the SIII. 1979 The Series III goes on sale in early spring, and would remain in production all the way through until 1992, in V12 form (not covered in this feature).


The XJ6 was a milestone car of the 1960s having taken some years to develop. Having won its 1969 Car of the Year award, the XJ6 graced the front cover of Car magazine in March of that year with the strapline “A very, very British Car of the Year”. Inside were no fewer than 12 pages devoted on the new model, including a fourpage road test. This was one special car let alone a new Jaguar, even if it didn’t get a top-three placing in the European Car of the Year (won by the NSU Ro80 in 1968 and the Peugeot 504 in 1969).

Jaguar’s aim was to sell the new XJ for at least seven years; in the event it managed to more than double that lifespan, with a pair of facelifts along the way. The saloon certainly impressed those at Car, who proclaimed “the Jaguar XJ6 impresses not just by what it is, but by the value for money it offers in its class – and this is a class which boasts some very worthy competition”.

That competition included the Mercedes S-Class and BMW’s large saloons, both of which were available with straight-six power. Which threw up an interesting question; was the Jaguar XK engine outdated? Car didn’t think so: “had the twin-cam XK engine been new yesterday, would anyone have called its concept in any way old-fashioned? On the contrary, we might have been pointing to some of its features as cunning touches which would make it that much easier to meet the ever-tougher pollution regulations which continue to spread eastwards from Los Angeles County”.

Autocar broadly agreed with Car’s findings and said its qualities were unrivalled at price “it is its overall excellence, though, that impressed us most.” While the road testers were blown away by the XJ6’s ride and handling what didn’t impress so much was the XJ’s packaging, its interior (in standard-wheelbase form) not feeling as roomy as it should have done for such a long car.

When the Series II arrived, the same monthly pitted it against the Peugeot 604 and BMW 528. The Volvo 264 and Renault 30 were also considered as rivals along with the Mercedes in concept – but not in price. Of the three that did make the group test, the BMW was dismissed first, as it wasn’t all that comfortable and despite its high price it wasn’t nearly refined enough. It also wasn’t as good to drive as the Jaguar, which handled better.

What seems incredible now though is how well the Peugeot fared; Car reckoned it ran the Jag close on several counts, not least of all comfort. Indeed, the monthly hailed the 604 “as a limousine is even more successful than the Jaguar” which is why the French contender won the group test.

Motor heaped its praises on the Coventry car, naturally, but let a passenger sum the XJ6 up best; “The bloody thing freewheels up hills!”.

We reckon that’s still an attribute many will still find with a good one and the Jag’s qualities shames many moderns – indeed its was hard to justify a Rolls-Royce above one – then and now.

Except on quality that is, which really started to slip under BL’s stewardship in the 1970s and why the SII is so slated, even though it’s a better car. Image too is just starting to become good again after being looked upon as a high class banger to smoke around in. And dare we say it, did Arthur Daley do the XJ’s cred any good? For most, the 4.2 is the logical pick. The sweeter 2.8 is a lot slower and fares little better at the pumps which you’d do well to better 20mpg. In fact, Autocar managed less than 16mpg, as did Motor with a SII, meaning that there’s not much difference between a hard driven XJ6 and a gently run XJ12 – worth a thought if you cover so little miles in your classic?


Ken Jenkins is a classic Jaguar specialist who has been working exclusively on the marque since 1967. With a workshop in Nottinghamshire, he maintains classic Jaguars (with a particular focus on engine rebuilds and upgrades), as well as selling new and used parts. A founder member of the Jaguar Enthusiasts’ Club, he’s also the Technical Director for the group. Find out more at

Says Jenkins: “Values have climbed sharply over the last year or so, but you’ve got to be incredibly careful when buying because there are so many misdescribed cars out there. Be especially careful when buying at auction because you probably SII much derided but a good one is better than the original won’t get the chance to inspect the car as fully as you might like – and you won’t get a chance to test drive it either”.

According to Jenkins, the bottom line for any XJ Series II is now between £4000 and £5000 while an equivalent Series II is an extra £1000 or so. But if you want a decent 4.2-litre Series I you should bank on spending at least £8000-£10,000.

The key thing is to buy something that’s genuinely good, and not just tarted up. However, some sellers don’t realise how quickly values have climbed recently though, so there are bargains to be had if you’re lucky but be quick.

Genuinely superb cars come onto the market only very rarely, and when they do you have to dig deep to secure one. The best Series II is worth around £15,000 – maybe slightly more. But an equivalent Series I can easily fetch £20,000 – perhaps even £30,000 if it’s something truly jaw-dropping. But even these figures are low compared with the XJC Coupé, which was offered only in Series II form.

These sell for over £30,000 if in superb condition, and it’s rumoured that an XJ12C sold for £60,000 recently – although this hasn’t been confirmed.
Jenkins continues: “The Series I has more of a following than the Series II, especially in 4.2-litre form, but both series are now surprisingly rare – many cars have been broken because they’re beyond viable restoration. The XJ is also popular with kit car builders and hot rodders which is why you’ll now have to pay at least £2000 just to buy a car for breaking. There are far more six-cylinder cars about than V12s, but the market for XJ6s is also that much greater – the 12-cylinder cars are wonderful, but inherently thirsty. It’s easy to dip below 10mpg if you use the huge performance on offer, and even if you drive gently you won’t see more than 15mpg.

“However, there’s an element of just buying whatever you can get hold of. With so few truly superb cars out there, it’s not a good idea to be too choosy about exactly what specification you want”. While it’s the 2.8-litre cars that are generally unloved, despite being perfectly usable, the 3.4-litre models aren’t especially desirable either. With low gearing, cloth trim and a thirsty engine, it’s no wonder that most have long since disappeared. What is in demand is the Vanden Plas, which came automatically in long-wheelbase form so it’s a proper limousine.


Even though some editions of the XJ weren’t very well put together, all are well engineered. For example, the transmissions are strong and so are the brakes, so as long as the car is maintained properly, these areas shouldn’t need to be beefed up. It’s the same with the suspension, although swapping to stiffer Koni, Gaz or Bilstein dampers is recommended, to sharpen up the handling and reduce the amount of roll in corners; an XJ12 front anti-roll bar is also worth fitting.

When it comes to tuning the engine, be very careful. The 2.8-litre unit isn’t a great starting point, so buy something with a bigger engine if performance is your priority. Even when you do start off with a bigger engine, don’t mess about with camshafts or cylinder heads as they don’t respond very well to tweaking. The easiest power gains are through changes to carburation; fitting SU or Weber 45DCOEs will increase the available power. The early HD8 carbs were the best, but you’re better off avoiding the later HIF7s with the AED automatic choke.

Ken Jenkins comments: “We fit the S3 big-valve head and camshafts as a first stage of tuning; the camshafts have a little more lift and overlap as well. Webers are not very easy to fit. The main silencers can be removed to increase power. These cars have to run on Shell V Power or similar, they like 28-30 degrees BTDC at 3000rpm with the vacuum off; the 2.8 needs about four degrees more. Any standard twin-carb car needs a free fuel flow of two litres per minute; early cars had a glass bowl fuel filter, later ones had a blue bowl one that will flow more. Finally, it’s also worth using DOT 5.1 brake fluid as this reduces the risk of brake fade”.

What To Look For



  • Six-cylinder XJs are far more common than V12s; of 403,732 XJs built, two-thirds featured the XK straight-six. Offered in 2.8 (Series I and early Series II), 3.4 (Series II and III) and 4.2-litre (all Series) guises, the XK engine needs regular maintenance or its life will be much reduced. Look for a service history, make sure the engine doesn’t sound hollow or rattly and ensure the oil is clean; walk away if it’s like tar. The key is to budget for a rebuild as soon as the engine is showing signs of wear; delay things and the bills will quickly mount.

  • All six-cylinder XJs feature an XK engine, with a cast-iron block and alloy cylinder head. Because of the latter, anti-freeze levels must be maintained or internal corrosion is guaranteed. Even a well-maintained engine will need a fresh radiator every 5-10 years depending on use, so you may need to budget for this at £220 plus fitting. Only ever use blue anti feeeze, make sure the the viscous fan coupling is tight to turn.

  • Expect oil pressure of 40psi when cruising, but senders and gauges can be unreliable so plumbing in a temporary gauge is worthwhile. Some oil consumption is normal, but lots of smoke on the over-run or when the throttle is blipped, suggests the valve stem seals have hardened or the valve guides have worn – or it could be that the breather pipe is blocked. Fixing the valve stem seals or worn valve guides will cost at least £1500 for the work, but complications can take this much higher.

  • Look at how much oil is on the car’s underside, as the rear crankshaft oil seal can fail. Once this has happened the engine needs a complete rebuild; a specialist will charge £4000 for the privilege or you could do the work yourself for upwards of £600 – but it’s an involved job. The best thing to do here is to machine the crank seal track and fit a lip seal conversion. If rebuilding a 4.2-litre engine, fit the high-compression pistons from the Series 3 engine while you’re at it.




  • Because of poor rustproofing, frequently poor build quality and values that have been on the floor for many years, bodged XJs abound so take care when vetting. n Few unrestored cars remain in a good condition, while many restorations aren’t very well done due to low values, so be careful if one looks exceptional. n Key rot areas incude the bottoms of the A-, B- and C-posts along with the sills, rear wheelarches and valances. These areas, along with the spare wheel well and the door bottoms are some of the more obvious places to check.

  • Less obvious are the rear radius arm mounts along with the arms themselves, the metal around the front and rear screens and the bonnet hinge mounting points. The bonnet itself can also corrode, as can the boot lid, wings around the headlights plus the various jacking points; check all these areas very carefully for filler by taking a magnet with you.

  • The radiator support frame also dissolves readily, which is an automatic MoT failure; if left to fester, rust then eats into the front chassis structure. Repairs are a big job on the XJ6 and even worse on the XJ12 because of poor access.



    • Tread carefully if you’re considering a restoration project, because costs quickly escalate; the bodywork is most costly to revive while the trim can also be alarmingly expensive to sort.

    • You’ll spend more restoring an XJ than an equivalent-condition E-type, yet the finished item will be worth far less – which is one reason why most people take the E-type route.

    • Much of the XJ’s appeal lies in its cabin, which is as luxurious an interior as you’ll find. Most XJs feature leather trim, but the 3.4 was introduced for the fleet market so it often came with cloth trim. Any interior that’s seen better days could cost big money to fix – as much as £4000 if all the trim needs TLC. Then there are the carpets and maybe the wood as well to put right. Don’t forget to check the headlining as sagging can be an issue.

    • Series II XJs suffered all sorts of electrical gremlins; early cars are generally better but you still must check everything carefully. Switchgear on earlier models could be horrifically unreliable, the powered window switches usually being first to pack in. Everything is available to put things right, but some bits are costly so be prepared for big bills if there are lots of problems.

    • Some Series II coupés have speedos that read low, as they’re fitted with a 3.31:1 diff but the speedo is calibrated for a 3.54:1. It’s worth checking the speedo against GPS to be sure.




    • Some XJ6s had a manual transmission, but all V12s and most six-cylinder cars featured an automatic. The autos featured a Borg Warner transmission until 1977, but from this point on, XJ12s had a GM400 unit.

    • Some Series I automatic transmissions can be clunky with their ratio changes, even when in good condition. However, later cars were better so ensure gear shifts are smooth; even if all seems well it’s worth inspecting the fluid for colour, level and condition. If it’s black and smells foul, a rebuild is on the cards, at £850 upwards. Whatever state everything is in, it’s worth servicing the gearbox when buying – it could transform things.

    • The manual gearbox is strong and most such transmissions were supplied with overdrive. If the overdrive seems slow to engage, it’s probably because the oil needs changing or has fallen below the ideal level; top up with EP 90 oil only.

    • Differentials are tough, but can leak oil. That wouldn’t be so bad, but those in-board rear discs are perilously close to the diff and end up getting covered in lubricant, which is an automatic MoT failure. Putting it right costs at least £1200; the seals often leak because the brakes have overheated, so you might need to rebuild the brakes as well. Finally, listen out for clonking from worn universal joints, although these are cheap and easy to fix. n A lot of XJ universal joints are cheap and don’t last long; expect to pay £45-£50 for a decent joint which should last for years.

    • When checking the rear wheel bearings, there should be a few thou of free play, felt by rocking the wheel side to side.

    • The rear brake flexible hoses need replacing every five years. They tend to collapse internally and the brakes will stay on as a result – potentially catching fire.

    • Most XJs featured power steering as standard – police cars and some early 2.8s didn’t. It’s generally reliable but it’s worth checking there are no leaks; slight weeps are common. Also ensure the fluid level is up to the mark; if it isn’t, the car probably hasn’t been looked after. It’s worth changing the fluid at service time, using Dexron 2.

Three Of A Kind

Replacement for the original XJ range and many reckon the best of the lot. Restyled by Pininfarina for a more up to date as well as roomier look, the S3 also boasted a proper five-speed manual transmission. Other changes included fuel injection for the 4.2 engine and a retuned chassis to accept new Pirelli radials. Build quality also improved over the SII although this XJ still lacked the stamina of a Mercedes or BMW of the same era.
For years, Silver Shadow values were on the floor which is why so many were broken for spares. Now, as with the Jaguar, the groundbreaking Roller is beginning to be appreciated for the turning point that it represented for its maker. Values are climbing and when it comes to a sense of occasion few cars can compete – including an XJ12. But running costs can be high, while restoration costs can be crippling. So buy very carefully.
ROVER P6 3500
ROVER P6 3500
You could opt for any classic Rover with the Buicksourced V8 – P5, P6 or SD1. All represent cracking value, all are incredibly usable and two of them (sorry SD1) were generally pretty well screwed together. With P5B values now very high, the V8-powered P6 represents cracking value if not quite the same sense of occasion. But the SD1 also offers a certain something, even if great examples are now hard to find.


Find a good XJ and you’ll be rewarded with one of the most relaxing driving experiences available anywhere. Nowhere is the old adage of Grace, Space and Pace more applicable than here; all three are offered in abundance. You don’t need to fork out very much for a minter and if you look after it there’s no reason why running costs should be prohibitively high – unless you’re aiming to do a high annual mileage in an XJ12.

Along with other experts, we’ve been predicting that XJ6 prices will start to rise and they have. So get in there fast while they are still affordable.

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