1983 BMW 635CSi E24 vs. Jaguar XJS HE and Mercedes-Benz 500SEC C126 – road test

The highest standards of technical excellence and innovation in the motor industry are not now to be found in the most expensive super-luxury cars available, but from the quality mass producers of Europe. These are the companies who are able to finance the required investment and at the same time apply the resultant technology to cars which are produced at economic production levels.

The irony is that the £50,000 plus Rolls-Royces and Aston Martins which trickle out of factories at Crewe and Newport Pagnell in very small numbers simply reflect a very high standard of build quality and prestige to their customers. The ‘best’ cars in the world, in terms of performance, refinement and general relevance to everyday driving conditions, can be bought for around half that price, and as we have concluded in the past, come from Jaguar, Mercedes-Benz and BMW.

In any price range there is an active demand for more expensive coupe version of saloons, and in this section of the market the pickings are particularly rich. It’s an intriguing question why buyers are prepared to pay more – so much more – for two doors less and a considerable sacrifice in rear seat space for the sake of styling.

But in any case Jaguar charge £20,693 for the XJS HE which is £922 more than the XJ5.3 HE, Mercedes-Benz ask £28,700 for the 500SEC C126 – £3131 more than the 500SEL V126 LWB (W126 as SWB), and at £22,950 the BMW 635SCSi E24 is £5155 more than the equivalent top-range 7-series saloon E23. A price span of almost £9000 – enough to buy a BMW 323i E21 – is most unusual in What Car?’s group comparisons, but in search of the ultimate coupe we feel that price must take second place to the car. Let us begin by saying that although these cars will only be within the reach of those who need not worry about the high cost heavy fuel consumption, each the three has benefited from economy technology in their engine and thus the fuel saving potential has been improved over their predecessors. This is an essential development of the cars to them more socially acceptable the fuel conscious eighties.

A V12 5345cc engine could considered an anachronism in 1 day and age, and indeed the ear V12s were so thirsty as to m their continued production unjustifiable. However, last year Jag applied the ‘High Efficiency’ concept – hence the HE lettering which has given the engine a new lease of life. Basically, by using the ‘Fireball’ combustion chamber, the fuel mixture swirl is improved allowing a higher compression ratio and thus more efficiency.

These changes are claimed by the company significantly to improve the Jaguar’s petrol consumption, and they say that figures of nearer 20 mpg are a reality compared with the almost single figure consumption of earlier cars.

The result of the Jaguar’s specification is a massive power output of 299 bhp backed up by 318 lbs/ft of torque at 3000 rpm DIN.

As a successor to the now legendary Jaguar E-type, and thus the sporting car in Jaguar’s range, some may feel it disappointing to find there is no manual transmission for the XJS. A GM 400 three-speed automatic gearbox transmits the power to the rear wheels, and the overall gearing has been raised slightly on these newer cars.

In common with the XJ saloons, the XJS uses the classic set-up of double wishbones and coil springs at the front, and lower wishbones at the rear with the drive shafts acting as the upper link. Twin coil springs and damper units per wheel are used. Anti-roll bars are fitted each end. Steering is power- assisted rack and pinion and the discs all round are servoed.

The Jaguar XJS is a big car. At over 36 cwts it is less than two cwts lighter than the saloon, and despite the fact that it is effectively a two-plus-two coupe, it is only seven inches shorter in overall length.

The handsome new Mercedes-Benz SEC C126 coupes are larger than the SLC models C107 / R107 SL based which they replace, but the emphasis is very much on economy with good aerodynamics and the Mercedes-Benz Energy Concept which has been applied to engines through-out the range.

On the V8 4973cc light alloy engine of the 500 SEC, the shaft timing has been more and the compression ratio is fully increased, together with shaped combustion champ give more efficient fuel consumption.

The end result is a torque out of 299 lb/ft at 3000 rpm, which lower engine speed than and a power output of 231bhp per cent less than the Jaguar produced at a fairly low 4750rpm. Other changes include an intelligent automatic transmission which has a raised final drive will change up into top goes soon as possible. However four-speed unit will still kick quickly when the throttle is firmly depressed. Idle speed is held constant at 500 rpm, and the fuel supply is cut off during overrun.

Front suspension is by double wishbones, and semi-trailing arms are used at the rear. Roll bars are fitted each end. Braking is by discs front and rear, and ABS anti-lock braking – a braking system which prevent skid-inducing wheel lock up no matter how hard or clumsily the pedal is pushed – is standard. Steering is by means of recirculating ball with power assistance.

There is little to distinguish the BMW 635CSi E24 from its predecessor – it has benefited from a ‘brain lift’ rather than a facelift. Under the bonnet there’s a new 3430cc six- cylinder overhead cam engine which produces 218 bhp and gives 224 lb/ft torque at 4000 rpm. These figures in fact being the same as those of the old engine.

It’s the ancillaries which represent the real improvements made to the 6-series. The ignition timing and fuel injection systems are programmed to give optimum ignition timing and fuel metering at all speeds and under all different conditions such as engine temperature, air temperature etc. Like the Mercedes-Benz there is an overrun fuel supply cut-off. The digital electronics also replace the regular servicing interval by ‘telling’ the driver when a service is needed.

Unlike the Jaguar or Mercedes-Benz, there are three different transmissions available; three- speed automatic, five speed manual close-ratio, to five-speed overdrive. Ours had the overdrive box.

BMW have made changes to the suspension of these new models although in essence it remains the same! Struts are retained at the front but they are now double jointed at the bottom to reduce wheel offset and thus reduce the steering pull which might be felt. At the rear trailing arms are still used but their angle has been reduced in answer to criticism that previous cars let go too quickly.

Steering is by recirculating ball with power-assistance, and braking is by front and rears discs, aided by the ABS system. Weighing in at 28.1 cwts, the BMW is the lightest of the three cars.


All three cars are very quick, that much we can take for granted. Up to 60 mph the BMW – least power but lightest and manually geared – is the fastest, reaching that speed in just under seven seconds, a clear second faster than the other two. It carries on to reach the 100 mph barrier in a little over 18 seconds and will reach a maximum of 140 mph. It’s just as well that a rev limiter cuts in at 6200 rpm – as it would otherwise be all too easy to forget how hard the engine is working, so sweet and refined is the BMW unit.

Sweet and refined that is, until you experience the Jaguar’s truly magnificent engine. With twice as many cylinders as the BMW it’s just in a different league, making the little 3.5-litre seem ordinary by comparison. Sheer effortlessness and silence is the name of Jaguar’s game; press a featherlight accelerator pedal (a further psychological boost) and coming on for two tons of high efficiency engineering surges forward with at worst only a hint of wheelspin from the well located rear wheels.

As we said, taking 7.8 secs to reach 60 mph makes it slower than the BMW, but thereafter it will leave both the German cars struggling, decreasing in size in the Jaguar’s rear-view mirror like the backdrop of a silent movie. By the time the 100 mph barrier comes up it has three seconds in hand over the BMW, and more than four to the Mercedes. Top speed, should there ever be a chance to use it, is the other side of 150 mph.

However both the transmission of Jaguar and BMW deserve a little criticism. The BMW’s manual change is fairly stiff and notchy, and the clutch is not only very heavy but has a long travel. Gear ratios are nice, though; second is enough to aim for any gap in the traffic under 60 mph, and third will match the Jaguar’s kicked down acceleration times from 30 to 100 mph. The XJS’s GM auto transmission can be just a little whiney in first, and when accelerating hard, changes up rather raggedly.

With ‘only’ eight Cylinders the Mercedes-Benz cannot match the performance of the Jaguar but the big car still picks itself up and shoots forward with the minimum of fuss. Unobtrusiveness is the main virtue here, and in fact it leads the driver to believe that he is accelerating slower than he is in reality, such is the diminished sensation of speed.

The acceleration figures are broadly similar to those of the 500SEL saloon, but the coupe felt a lot livelier because the kickdown is much more responsive, and unlike the saloon we did not need to be manually overriding the four speed automatic box for maximum acceleration. 60 mph is reached in the same time as the Jaguar, 70 is made in 10 secs, and 100 mph exactly double that.

The transmission is better than the Jaguar’s with the change being virtually imperceptible and the gears merging into one another with no jerking which one can notice on the XJS. Maximum speeds in the gears are 40, 75, 130 and 140 mph.


A racing car style suspension allied to good road tuning has really set the Jaguar up well. Together with the XJ saloon ride comfort is superb and probably better than that £50,000 luxury car from Crewe. Road bumps are heard rather than felt – it’s the closest any manufacturer has come to the imaginary magic carpet.

Better still is that the Jaguar has outstandingly good roadholding and handling, especially for car so heavy. There is virtually no roll and the excellent ride has not been achieved through resorting to a soft suspension. Indeed the XJS can be poured into tight bends with the confidence one would have with, say, a nimble Alfasud. The main difference is of course with just under 300 bhp available at the brush of an accelerator pedal, care is needed to stay straight.

But there’s still that power steering problem. At the rim, the weight is far too light and the faster one drives, the less response seems to be fed back. Things aren’t helped by that skinny steering wheel – a smaller leather rimmed one would be much better. The weight is better than it used to be but it still needs improvement.

Whatever improvements BMW have made by reducing the angle of the rear trailing arms to 15 degrees, they are not enough. That much is evident in standing starts when the rear wheels squat down and the tail swings wildly outwards, despite the limited-slip differential which is standard.

The early transition to sudden oversteer on lifting off power has been reduced on the new 635 E24, but it is still so easy to have the tail end sliding out under power – even fairly modest power. The classic situation is likely to be on exiting a wet roundabout and trying to put too much power down.

Aside from this, the BMW feels the nimblest of the three cars, and once the driver is seated inside, it seems to lose its big car proportions and fits like a small and neat glove. Steering is superb; beautifully weighted and delightfully precise, and the front end of the car responds to the wheel as quickly as it can be turned.

BMW 635CSi E24 super steering but can be tricky in wet.

Jaguar XJS good ride and handling marred by light steering.

Mercedes-Benz 500SEC C126 vague power steering but excellent chassis.

But in ride comfort the BMW is not in the same class as the other two. It feels firm and hard, down- right uncomfortable next to the XJS, and matters are of course not helped by those big low-profile TRX tyres. It’s also a little disappointing to discover that the car displays a degree of body roll which is not justifiable with that sporting suspension tuning.

The Mercedes-Benz has an excellent chassis but its good roadholding is not done justice by the vague steering. It turns into corners very well, and this huge car can be quickly and tidily exited without the dramatic tail slide of the BMW (although that does come ultimately) but its the car in this group that drivers would least want to use in that way. It presents itself as far more a cruiser than a sportster. The ride comfort is almost as good as that of the Jaguar with a feeling of isolation From the road and all its problems, but there is more intrusion from road surfaces.

Two of the three cars have an anti-lock braking system fitted as standard – the Jaguar does not. However in normal, even very quick driving that doesn’t prove to be a huge disadvantage. The Jaguar’s discs bite powerfully without any obvious early lock-up. Ultimately, emergency braking will be safer on the German cars, and 26 that kick back and vibration through the pedal under really hard braking as the system enacts a cadence motion, is reassuring once a driver is used to it.


Here’s where one must really doubt the wisdom of buying an XJS in preference to an XJ saloon. Despite the fact that the coupe is hardly any shorter, the rear seats are suitable only for children, and not only that but are pretty inaccessible too. The XJS is effectively a two seater, and that’s a big inconvenience.

Room is not restricted in the front but the seats are not terribly comfortable though in fairness it should be said that they are little worse than those in the saloon. Seat back adjustment comes in coarse amounts by means of a chromed lever and there is not an abundance of rearward travel. The driving position is very low and shorter drivers will have restricted vision of the car’s extremities due to the high waistline – and they will long for a seat height adjuster. The transmission tunnel inside the XJS is huge: consequently there is nowhere to put one’s left foot.

The desirability of leather seating tends to be a matter of opinion and there’s no doubt it looks very smart in the XJS, but we would like to see cloth upholstery as an alternative. Leather is slippery and it is difficult to locate oneself in one’s seat when braking or cornering at high speeds.

The Mercedes-Benz seats are near perfect, and sum up this company’s attitude towards achieving perfection. Front seats are firm but prove immensely comfortable over long distances, and have what must be the ideal means of adjustment. On each door there is a little switch in the profile of a seat which electrically moves the two portions of the seat according to how the switch is moved. By this system, driver and front passenger can specify their exact seating position rather than choosing from what’s available. It should be said that this is an optional extra.

Rear seating is good, too, with proper seats which will comfortably take two adults, and at a push three smaller children. There won’t be room to stretch one’s legs in the same way as it is possible in the saloon version but the seats are not an afterthought like those in the Jaguar.

The BMW seating is somewhat disappointing. The seats are well shaped in the front but they are just so hard and, unlike many hard seats, do not prove themselves over a long distance to be comfortable. Perhaps half the problem is down to the driving position not being perfect – certainly an odd fault for BMW. Although the seats have good adjustment It is difficult to find a comfortable position in relation to the pedals which need firm pressure in any case.

Like the Mercedes-Benz, rear seating is good given the limitations of the coupe body but in this case they are uncompromisingly for two people and with not over large frames at that. Nevertheless headroom and legroom are both reasonable.

Luggage capacity varies from good to bad; best on the Mercedes-Benz which has a reasonably sized boot, and worst on the Jaguar which also has to play host to the huge spare wheel and air conditioning unit situated at one end. The BMW’s boot area falls midway between the other two and is very practically trimmed.

Driving position BMW E24 is uncomfortable with hard seats, notchy gearbox and heavy clutch. Dashboard has few dials but is ergonomically excellent. Big six-cylinder engine is powerful and economical.


In this league of cars one expects very high levels of refinement, and by and large all three cars are luxurious to drive and live with.

All are very quiet, but the Jaguar is still the quietest here, and the quietest car we know. It is totally silent at most speeds, and the only intrusion is some wind noise towards the 100 mph mark and the occasional whirring from the air conditioning.

The Mercedes-Benz is almost as silent with the engine virtually in-audible unless revved hard. The main source of noise is as wind swirls around the body pillars and tyre roar which intrudes on rough road surfaces. In this company the BMW is the ‘noisy’ car with a lot of wind turbulence at speed.

Both Mercedes-Benz and Jaguar have full air conditioning systems whilst the BMW has an ordinary but sophisticated heating/ventilation system. The Jaguar’s system is simple and works well – one selects the required temperature down on the centre console and then leaves it to regulate itself. Mercedes-Benz offer two independent controls for either side of the cabin controlled by means of a simple rotating knob.

The BMW’s system gives good heat and cooling but cannot match the full systems of the other two cars. Proper air conditioning is available for an extra £1234.

Mercedes-Benz and BMW offer clean, simple and easy to read January 1983 facias. BMW in fact has really quite basic instrumentation but the big main dials and auxiliary instruments are beautifully simple and well designed. Simplicity and practicality is also the theme of Mercedes-Benz facia and everything is contained in three dials ahead of the driver. They look good, but the four small instruments in the left hand one can be a little difficult to assimilate quickly. There is one main steering stalk – it operates wipers, indicators and dip.

The Jaguar’s facia has a certain old fashioned elegance about it, with expanses of wood and chrome, but against the Mercedes and BMW it is a glaring weak spot. The main dials look cheap, and the minor instruments are hard to read at a glance. Worst point is the cheap looking clock stuck in the centre console. And why the need to hide the lights switch down to the left of the steering column? No points either to the cruise control which needs a column stalk plus a switch near the gear selector. Mercedes-Benz can make do with just one simple stalk. Jaguar switches are also cheap looking and lessons must be learned from BMW and Mercedes-Benz.

With the German cars having quite a high commanding driving position they have good all round visibility, but unfortunately this is not the case on the Jaguar. The driver sits low and those massive pillars make big blind zones.

The BMW contains a mighty trip computer in the centre of the dashboard which we suspect that few drivers apart from trained computer programmers will understand and make most use of. It takes two pages of the handbook explaining how to set it up.

Where electronic gadgetry is the forte of the BMW, Mercedes-Benz offer some simple but devastatingly clever electric devices. That seat adjuster we have mentioned is excellent and there is a seat belt feeder which activates itself when the driver turns on the ignition. Arms come out from the seat belt mounting points and offer front occupants the belts.


The Mercedes and BMW are beautifully put together, and there is some evidence that the tarnished image of Jaguar’s quality control is improving. A massive quality drive has identified many weak points but of course only time will tell if the sight of broken down Jaguars on motorway hard : shoulders is now one of the past.

Reading the fuel returns of two big cars – the Mercedes and Jaguar – is depressing as average 16.5 and 14.2 mpg relatively. However, seen against performance of previous m there appears to be a signed improvement.

Driven normally the Jaguar give over 17 mpg, and although hardly a good reading is scantly better than the origin, cars which could only just s double figures. Without using much of that performance the Mercedes-Benz can reach 18 mpg better than the 16 mpg best a 500SEL V126 saloon we have which did not benefit from energy concept.

The best fuel consumption figures from the BMW which retrieve over 20 mpg – good consumption considering the performance the way the car was drive every occasion save our test session when it gave just over 19 mpg. The best was 23.3 mpg, those should be noted that with the ratio gearbox specified the fuel consumption is likely the heavier.

Servicing costs will inevitably heavy on all three cars. The Mercedes-Benz needs a major service at 12,000 miles, the Jaguar at 10,000 miles. The service indicator the BMW tells the driver when a device is due, rather than having mention at regular intervals. The smaller spread of 350 favours the regular, whilst the BMW owner can be it to 147 garages and Mercedes-Benz have 94 dealers.


Comparison verdicts favouring a Mercedes-Benz over a Jaguar are rare in the motoring press, but we have to record one here, and we would chose the 500SEC C126 as the winner. Whereas the XJ saloon – despite its faults – is a more desirable car than the 500SEL V126, the XJS simply does not add up to a good enough coupe to beat the Mercedes.

The fundamental fault with the Jaguar is that it offers nothing over the XJ saloon. The engine is magnificent and the chassis is superb but then these qualities are common to all Jaguars, and the saloon has proper rear accommodation together with a beautifully proportioned body. That’s definitely not something one could say about the XJS, especially considering the very heavy looking rear three quarter angle and massive bumpers. It’s such a shame that the XJS is such an ugly car – Jaguar have never produced one before.

On the other hand, the Mercedes-Benz 500SEC C126 is an outstandingly successful coupe, sacrificing very little over the SEL V126. Rear seating is good, as is luggage space, and all the controls within the car are ridiculously simple compared to some of the muddled functions of the Jaguar. The engine and chassis do not match that of the Jaguar but the big V8 is still beautifully refined and it is almost as much a driver’s car.

The only real criticism one could make of the 500SEC is that it is a car lacking in character and for all its perfection it cannot stir the same emotions as the British car can. Approaching £30,000 it is not exactly cheap but over several years depreciation levels might even out the difference.

That leaves the BMW which is an excellent car, but one which is in a different class. Whereas one would happily drive very long distances in the other two and feel just as fresh at the other end, the BMW is less comfortable, has too hard a ride and suspension, and is much too noisy to be considered as a true luxury car as the Mercedes and Jaguar can.

It’s clearly the sporting car of the trio and is one which will give the most enjoyment to the driver beloved of continual opposite lock driving and tearing away from traffic lights. But that engine sounds positively frantic against the eight and 12 cylinders of the other two, and those who seek the finesse of the ultimate coupe available will be disappointed.

Scrappy switches and cheap-looking instruments make Jaguar look outdated; seats are too low set and rear space is minimal. Magnificent V12 is unsurpassed for smoothness and HE is less thirsty

Seating is easy best of the group. Controls are very simple indeed lacks Jaguar’s ultimate refund in but has better economy.

CAR BMW 635CSi E24 Jaguar XJS HE Mercedes-Benz 500SEC C126
PRICE 1983 UK £22,950 £20,693 £28,700
Other models 2 2
Price span 1983 £17,895-22,950 £20,693 £21,720-28,700 
Max Speed (mph) 139 152 140
Max in 4th (mph) 140
Max in 3rd (mph) 101 135
Max in 2nd (mph) 64 115 75
Max in 1st (mph) 37 67 40
0-30 (sec) 2.8 3.3 3.5
0-40 (sec) 3.6 4.7 4.8
0-50 (sec) 5.2 6.0 6.1
0-60 (sec) 6.8 7.8 7.9
0-70 (sec) 8.6 8.6 10.0
0-80 (sec) 11.6 10.8 12.9
0-90 (sec) 14.4 13.3 16.8
0-100 (sec) 18.1 15.8 20.0
0-110 (sec) 22.4 19.4 27.0
0-400 metres (sec) 16.1 15.8 17.1
Terminal speed (mph) 96 100 91
30-50 in 3rd/4th/5th (sec) 4.1/6.2/9.8 3.9** 4.5**
40-60 in 3rd/4th/5th (sec) 4.3/6.4/9.4 3.5 4.2
50-70 in 3rd/4th/5th (sec) 4.7/7.7/10.5 4.5 4.4
60-80 in 3rd/4th/5th (sec) 4.9/7.7/10.5 4.7 5.6
70-90 in 3rd/4th/5th (sec) 5.2/7.9/11.3 5.2 8.0
80-100 in 3rd/4th/5th (sec) 6.5/8.6/13.0 5.7 7.1
Cylinders/capacity (cc) 6/3430 M30 V12/5345 V8/4973
Bore stroke (mm) 92×86 90×70 96×85
Valve gear ohc ohc ohc
Compression ratio 10.0:1 12.5:1 9.0:1
Induction injection injection injection
Power/rpm (bhp) 218/5200 299/5500 231/4750
Torque/rpm (lbs/ft) 224/4000 318/3000 299/3000
Steering PA/recball PA rack/pin PA/rec ball
Turns lock to lock 3.3 3.0 3.0
Turning circle (ft) 34.0 37.4 37.8
Brakes S/Di/Di S/Di/Di S/Di/Di
Suspension front l/McP/A l/Wi/C/A l/Wi/C/A
rear C-/STA/A l/Wi/C/A l/STA/C/A
Test mpg 19.2-23.6 12.6-17.4 13.8-17.9
Govt mpg City/56/75 18.0/39.2/32.1 15.0/26.8/21.5 18.6/31.0/24.8
Tank galls (grade) 14.5(4) 20.0(4) 19.8(4)
Major service miles (hours) see text 7500(4.0) 12,000(3.4)
Part costs (fitting hours)
Front wing £261.98(3.8) £145.00(N/A) £80.47(4.3)
Front bumper £171.56(2.7) £46.50(N/A) £252.45(0.4)
Headlamp unit £22.49(0.5) £52.00(0.3) £111.60(0.7)
Rear light lens £30.91(0.5) £20.00(0.3) £49.38(0.4)
Front brake pads £20.49(0.5) £29.75(0.6) £10.75(0.6)
Shock absorber £67.02(1.3) £22.50(0.6) £34.01(0.6)
Windscreen £99.85(1.3) £95.00(4.3) £215.82(3.7)
Exhaust system £437.28(0.6) £397.90(N/A) £330.82(0.8)
Clutch unit £81.22(2.5) N/A N/A
Alternator £180.11(0.5) £120.75(1.2) £153.64(0.8)
Insurance 9 9 9
Warranty 12/UL 12/UL 12/UL
Anti-rust 6yr none none
Automatic transmission Optional Std Yes
Five-speed gearbox Yes N/A N/A
Air conditioning £1234 Yes Std
Anti-lock brakes Yes No Yes
Trip computer Yes No No
Cruise control Yes 340 Yes
Adjustable steering column Yes Yes No
Radio/Cassette No Yes No
Leather trim Optional Yes Optional
Seat height adjustment Yes No Yes
Rear seat belts Yes No Yes
Sunroof Yes No Yes
Headlamp wash-wipe Yes £226 Yes
Front headroom (ins) 36 35 37
Front legroom (ins) 33-39 35-43 33-44
Steering-wheel-seat (ins) 11-18 14-20 12-24
Rear headroom (ins) 34 32 36
Rear kneeroom (ins) 32-40 20-26 19-31
Length (ins) 187 191.8 193
Wheelbase (ins) 103 102 112
Height (ins) 54 50 55.3
Boot Load height (ins) 33 23 33
Overall width (ins) 67.9 72 72
Int. width (ins) 53 56 57
Weight (cwt) 28.3 36.1 31.1
Boot capacity (cu. ft) 14.5 10.9 17.3
KEY. Valve gear: ohc, overhead camshaft. Steering:rack/pin, rack and pinion; rec ball, recirculating ball; PA, power assistance.Brakes: Di, discs; S, servo assistance.Suspension: /, independent; C, coil springs; Wi, wishbones; McP, MacPherson struts; STA, semi-trailing arm location; A, Anti-roll bar.’estimated * *acceleration in kickdown on automatics.


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