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Jaguar XJS V12

Published: 1st Jun 2011 - 1 Comments

Jaguar XJS V12
Jaguar XJS V12
Jaguar XJS V12
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Every 6000 miles, while the components removed for spark plug access are still out of the way, check the state of the high tension leads (these can be damaged by heat as they are very close to the engine) and remove the distributor cap to examine its segments, also check the rotor arm.


XJ-S V12 1975-93: Overhead camshaft V12. 5343Cc, 285 bhp to July 1981; HE, from July 1981, 299bhp. 1993-96:V12, 5994cc, 308bhp.

Valve Clearances

The valve clearances are controlled by shims. Adjustment is not a routine maintenance item; normally the clearances should only need to be reset if the cylinder heads are disturbed.


Firing order (R = Right bank; L = Left bank; cylinders numbered from front of engine): 1R-6L-5R-2L-3R-4L-6R-1L-2R-5L-4R-3L

Spark plugs: Pre-HE engines, Champion N10Y or equivalent; HE engines, Champion BN5 or equivalent. Gap 0.025in. (0.64mm.). Check/clean plugs every 6000 miles (using brass-bristled brush); renew plugs regardless every 12,000 miles.ALWAYS blow dirt from the plug wells before unscrewing the plugs. To reach the two forwardmost plugs in each cylinder bank, remove the air con compressor. For easier access to the plugs further back, ideally take off the throttle ‘tower’ and the ignition coil, also the cruise control ‘bellows’. Note that the plugs are taper seat varieties. Lubricate the threads when installing the plugs, and initially tighten by hand until the plug seat contacts the cylinder head, then rotate a further 1/16th turn (the torque setting is no more than 8lb.ft.). Avoid over-tightening the plugs, or they can be EXTREMELY difficult to remove afterwards. Every 6000 miles, while the components removed for spark plug access are still out of the way, check the state of the high tension leads (these can be damaged by heat as they are very close to the engine) and remove the distributor cap to examine its segments, also check the rotor arm. Breakerless electronic ignition is employed, so the timing should not alter between services although it can slip. For the record, the settings are:

Pre-HE units: 10 degrees BTDC @750 rpm, with vacuum pipe disconnected.

HE units: 18 degrees BTDC @ 3000 rpm, with vacuum pipe disconnected.

Fuel System

Every 5000 miles or annually (whichever comes first), check the state of the air filter elements (one for each cylinder bank, and fairly easy to reach; the filter housing lids are secured by ‘over centre’ type clips), renewing if visibly dirty. Change the filters every 20,000 miles regardless. Always wipe out the filter housings with clean rag before fitting new filter elements. On completion, ensure that all securing clips are properly engaged. Every 10,000 miles/annually, examine all fuel system pipework. On pre-HE models, the rubber feed pipes linking the injector rail to the injectors tend to become brittle and can come loose, causing a potential fire hazard. Renew any doubtful looking pipes at once. Every 60,000 miles, renew the fuel filter, located in the boot.To avoid excessive loss of petrol at high pressure, fit hose clamps to the pipes on each side of the filter, before removing it, then release the pipe securing clips and unscrew the filter from the bracket (a little leakage of fuel is inevitable - NO SMOKING!). Make sure that the new filter is the correct way round (note arrow direction on the unit). When the filter has been fitted, fully tighten the hose clips, and remove the pipe clamps. Run the engine for a few minutes, checking for petrol leaks. At every service, apply injector/fuel system cleaner, then check the idle speed, which should be 750±25 rpm.


Engine oil: Ideally, change the oil and renew the filter at least every 3000 miles or annually (whichever comes first), having first taken the car for a run to warm the oil and aid flow from the sump.The sump plug requires a 7/8in. AF socket or ring spanner. Apply a little fresh engine oil to the filter’s sealing ring, on installation. On completion, ensure that there are no oil leaks. Use a high quality lubricant, to minimum specification API SE/SF, and with a viscosity rating of SAE15W50 or 20W50. Please dispose of the old oil in an environmentally friendly manner – local councils provide waste oil collection points.

Sump capacity: Approx. 20 pints (11.4 litres), including the filter.
Note: Engine oil leaks from around the unit are commonly encountered; at each service check for and rectify such leaks before they can result in a serious loss of lubricant.

Transmission lubrication: At each service, with the vehicle horizontal, check the lubricant levels in the automatic gearbox and the differential. Check for leaks from both units, and rectify at once. The transmission dipstick is located under the bonnet, on the driver’s side of the engine. Use Automatic Transmission Fluid (ATF). Every 60,000 miles (approximately) - or earlier if the gearchanges become ‘lazy’ - drain the transmission fluid by unbolting the auto gearbox sump pan. Clean the sump and the gauze filter prior to reassembly and refilling with fresh ATF.
Note: If the old fluid is discoloured, the transmission is soon due for overhaul. Automatic transmission capacity (‘dry’, approx.): 16 pints (9.1 litres). The differential has a combined filler/level plug and a separate drain plug. The oil should be up to the base of the threads in the unit. Every 20,000 miles (approximately), drain the final drive unit (after a run, when the oil is warm and flows more easily) and re-fill with fresh lubricant.

Differential oil: Duckhams Hypoid 90DL or equivalent (a lube specifically intended for limited slip differentials). Differential oil capacity (approx.): 2.75 pints (1.6 litres). Every 3000 miles, re-grease the driveshaft universal joints, and check condition of driveshaft couplings at same time.


At every service: Check the master cylinder and reservoir for leaks (investigate if the fluid level is low), also assess the condition of the fluid. Check brake servo operation and assess hose condition/security. Inspect all fixed and flexible pipework; renew if damaged/corroded. Inspect the front brake pads, discs and calipers; renew the pads if the friction material is badly worn. Replace the discs in axle sets if their working surfaces are seriously worn/scored/corroded. Investigate reasons for uneven pad/disc wear. The inboard-mounted rear brakes are notoriously difficult to reach. If the rear axle/suspension assembly is ever removed from the car, it is a good idea to fully service the brakes, and replace leaking oil seals, at the same time.
Check especially for seized rear caliper pistons (more likely on cars which are used infrequently), also for oil contamination on the discs/pads. Ensure that the handbrake mechanism moves freely (an old Jag foible), and make sure that the rear brakes are locked with the handbrake fully applied (consult manufacturer’s literature). At least every 24,000 miles/two years whichever comes first), flush out and renew the brake fluid.

Cooling SYstem

Proper maintenance of the cooling system is of the utmost importance on an XJ-S; if this is neglected, internal corrosion (particularly within the cylinder heads) plus overheating WILL result. Use high quality anti-freeze mixture containing corrosion inhibitors, and leave in the system all year round to guard against corrosion. Every 3000 miles/annually (whichever comes first), check the radiator, the fan, all hoses (especially the bottom hose, which is vulnerable to being covered in oil), the header tank (which can rust through from inside). Check also for dirt which collects between the main coolant radiator, the air conditioning condenser and the oil cooler (beneath). Carefully clean this area, after releasing the upper front crosspanel (a build-up of debris here encourages overheating/cylinder head gasket failure). Inspect also the lower section of the radiator. At least every two years, drain the system, flush and re-fill with fresh anti-freeze solution.Capacity, with heater (approximately): 37 pints (21 litres).

Drive Belts

At each service, check all drive belts and renew if worn/damaged (replace in any event every 60,000 miles). There are four belts: One driving the fan, and one each for the alternator, power steering and air conditioning. To renew the alternator belt, first remove the power steering belt (but you don’t need to remove the air conditioning system belt). In each case, deflection under firm finger/thumb pressure should be approx. 1/2in. (13mm.). Each belt is provided with a separate adjustment mechanism.

Running Gear Components

Every 3000 miles/annually: Examine coil springs, watching for breakage/corrosion, and for rusting around the spring turrets on the front cross-member assembly. Check all shock absorbers for worn bushes and leakage. Examine the upper wishbone bushes, plus the upper and lower ball joints; all these need to be replaced as soon as any wear is detected. Checkthe rear radius arms; these suffer from corrosion, and their integral rubber bushes deteriorate. Fitting new arms is not usually difficult. Check the outer, lower rear suspension fulcrum bearings (replacement is a long job).Inspect the anti-roll bar link assemblies; look for worn bushes, also for elongation of the steel washers – which then move along the hexagonal part of the bar. Scrutinise all suspension/steering unit mounting bushes; renew in sets if worn. Examine steering rack gaiters, also those on all ball joints. Assess steering column and ball joints for wear. Check for oil leaks from steering rack shaft seal. Every 30,000 miles, clean and examine the front wheel bearing assemblies; renew the bearings if pitted, worn or noisy. On re-assembly, re-lubricate with fresh (wheel bearing suitable) grease.


Every 3000 miles or annually (whichever comes first): Re-lubricate all hinges and catches (wipe off excess lubricant afterwards). Check the cleanliness and security of all electrical connections; inspect all wiring for damage. Assess condition, security and tightness of the road wheels; closely inspect the aluminium alloy wheels (for impact damage and corrosion) and the tyres. Inspect underbody, rectifying any paintwork damage discovered. Ensure that all underbody nuts/bolts are fully tight. Check body shell for water leaks. Examine the exhaust system, particularly the front downpipes, which are vulnerable to corrosion (stainless replacements are a good option). Assess seat belt condition. Check all fluid levels. Check/re-adjust headlamp beam alignment.


For enthusiastic assistance with this feature, grateful thanks to: Hollygrove (Jaguar specialists), Tel: 01425 477000

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User Comments

This review has 1 comments

  • thanks for the info, I was just looking for info regarding the fuel injector hoses, mine need replacing, and it goes into the shop wednesday, I also bought a fire extinguisher.

    Comment by: donna     Posted on: 28 Nov 2011 at 02:16 PM

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