When Jaguar swept aside its entire range of saloons in the late-1960s and replaced them with just one model (the XJ6), not even the famously money-conscious marque could have envisaged that the basic design would endure for 41 years. The mould set under William Lyons in 1968 wouldn’t be broken until 2009, when the completely re-shaped XJ model came along. However, the Jaguar XJ6 didn’t make it through to middle age without a few nips and tucks along the way.
The original Series I cars were made until 1973, when the demands of safety, environmental issues and British Leyland penny-pinching dictated a metamorphosis into the Series II. It was, in many ways, something of a disappointment after some of the great Jaguars of the past, so when the time came for a further revamp, Jaguar decided not to take any chances and brought in a foreign designer for the first time in its history.
The Series III, launched in 1978, still kept the familiar handsome XJ6 shape, but the hand of Pininfarina was in the finer details. The roofline was raised, the glasshouse deepened, bumpers went from pure chrome to chrome-topped black rubber, the trim was improved and flush-mounted door handles were fitted. All these factors made the car look sleeker and even better proportioned than before. The exterior was matched by a re-worked interior that dispensed with the slightly cheap and tacky look of the SIIs.
At launch, there were three Jaguar variants (3.4- and 4.2-litre XJ6 and 5.3-litre XJ12), alongside four Daimlers (Sovereign 4.2, Double Six, Vanden Plas 4.2 and Vanden Plas 5.3. Prices ranged from £11,189 to £20,277, and that was before customers started ticking option boxes such as air conditioning (£988), or an electric sunroof (£461).
Pininfarina’s flourishes so revived interest in the XJ range that major modifications through the SIII’s life were confined largely to correcting teething troubles all the way to its end in 1992.

VITAL STATISTICS
Engine 4235cc/6-cyl/DOHC
Power 205bhp @ 5000rpm
Torque 236lb ft @ 3700rpm
Top Speed 127mph
0-60mph 10sec
Economy 16.8mpg
Gearbox 3-speed automatic

 
It takes a special kind of car design to actually suit ‘Portland Beige’ paint (actually a sort of pale yellow) and a vivid tan leather interior, but somehow this Jaguar XJ6 SIII manages to look terrific even with this combo.
It feels it, too – this car may have been manufactured during the latter BL years, but the doors still open and close with a bank vault ‘thud’, the walnut veneers glow and the leather smells heavenly. Rubber bumpers or not, this feels every inch a proper Jaguar.
It certainly goes like a proper Jaguar, but only if you have a little insider knowledge. In truth (and new Bosch L-Jetronic fuel injection notwithstanding), performance can feel a little underwhelming if you simply leave the transmission in ‘D’; it might pack a 205bhp punch, but this is a 1760kg car after all. An abruptly heavy right boot will instigate kickdown, but even then, acceleration feels more relentless than startling.
The trick is to hold the car in first gear all the way to the redline and then drop it back into ‘D’; Autocar shaved nearly a second off the 0-60mph sprint and a whopping 1.6 seconds from rest to 110mph using this apparently Jaguar-recommended method during its 1979 road test of an early SIII.
In truth, though, unless you’re Edward Woodward’s 1980s TV hero, Robert McCall, chasing down another bad guy in The Equalizer (he drove a black XJ6 SIII), this seems like overkill. There’s plenty of power to make overtaking a breeze, but this is a relaxed high-speed cruiser, not a wham-bam sprinter.
That said, the SIII lost none of its predecessors’ appetite for blasting along challenging B-roads. Jaguar wound down the level of steering power-assistance for the new car, prompting Autocar to describe its combination of ride, handling and roadholding as ‘superb’. The same is true today. The car belies its considerable heft with a level of deftness in the bends that beggars belief, considering how effortlessly it smothers poorly-metalled road surfaces.

Expert’s view
"A good XJ6 will be a reliable and comfortable car, but like everything it has its weak points. Rust is the main culprit, so check around the front and rear windows, rear valance and boot floor, and the sills. Lift the carpet to check the floor for signs of rust. Front chassis legs and cross member can corrode and will be expensive to fix."
"Mechanicals are usually solid, but check for a leaky or noisy diff and a noisy cylinder head. Pulling under braking can be due to seized calipers. A full service at a decent garage should cost no more than £300, so not as expensive as you might think. An entry-level car with an MoT can be had for £1200, but a good car with full history will cost upwards of £5000. They are now becoming relatively scarce and are still proving to be a reasonably priced British classic."
- Thomas Barclay, Jaguar Specialist
Thomas Barclay has worked on Jaguars for many years and is also heavily involved in historic racing.