Jaguar XJ6, Known Issues and Common Problems
Overview
The XJ6 is a complex luxury car built over a 24-year span. The problems you’ll encounter depend heavily on which series you own and how well it’s been maintained. A well-cared-for Series 3 with Bosch ignition and a documented service history is a genuinely reliable classic. A neglected Series 1 with Lucas everything and no maintenance records is a rolling restoration project.
The themes are familiar to anyone who’s dealt with Jaguars of this era: rust kills the body, Lucas kills the electrics, and neglect kills everything else. The XK engine is fundamentally robust, it was designed in the 1940s and perfected over four decades of production. The running gear is proven. The XJ platform was the finest chassis of its generation. When these cars are right, they’re brilliant.
When they’re wrong, they’re expensive. But nothing on this list is a mystery. Every problem is well-understood, every fix is documented, and parts are available for virtually everything. The XJ6 community, through the JDCA and online forums, is one of the most knowledgeable and generous in the classic car world.
Bodywork and Rust
Sill corrosion (structural)
What happens: Outer sills bubble and perforate. Inner sills rot silently behind trim. The car’s rigidity decreases, doors sag, gaps become uneven, and the body flexes over bumps.
Why it happens: Water enters the sill box sections through blocked drain holes, failed door seals, and stone chip damage. The inner sill rots first, hidden from view. By the time the outer sill shows rust, the inner structure may be gone.
How to fix it: Full sill replacement, outer and inner. The car must be properly supported (ideally on a jig) during the work to prevent distortion. Replacement panels are available for all series. Budget $4,000-8,000 AUD for professional sill repairs on both sides.
Severity: Critical. The sills are structural. Rotten sills make the car unsafe.
Floor pan corrosion
What happens: Floor pans rot from underneath or from above (water sitting under carpets). In severe cases, you can see the road through the floor.
Why it happens: Water enters through failed windscreen rubbers, door seals, heater matrix leaks, and blocked drainage. Sound deadening material holds moisture against the steel. Carpet and underlay hide the damage until it’s severe.
How to fix it: Cut out the rot, fabricate or buy replacement floor sections, weld in. All carpet, underlay, and sound deadening must come out for proper inspection and repair. Budget $3,000-8,000 AUD depending on extent.
Severity: Critical. Structural component.
Rear wheel arch and lower rear quarter corrosion
What happens: Rust appears at the bottom of the rear wings, around the wheel arches, and in the lower panels between the wheels and boot.
Why it happens: Stone chips, trapped mud, inadequate drainage, and the general tendency of British steel to rust when given the slightest encouragement.
How to fix it: Cut and replace affected panels. Repair sections are available. Budget $1,500-4,000 AUD per side depending on severity.
Severity: Needs attention. Cosmetic at first, but progresses to structural if the inner arch is affected.
Boot floor and spare wheel well corrosion
What happens: The boot floor rusts through, the spare wheel well fills with water, and the rot spreads to surrounding panels.
Why it happens: Boot lid seal failure, blocked drain holes, condensation, and (on some cars) battery acid leakage from the boot-mounted battery.
How to fix it: Replace the boot floor section. Check and replace the boot seal. Clear all drains. Relocate the battery if acid damage is an issue (some owners move it to the engine bay). Budget $1,500-3,000 AUD.
Severity: Needs attention. The boot-mounted battery and electrical components are at risk from water.
Front wing corrosion
What happens: Bubbling around headlights, indicator mounts, and the bottom edges of the front wings.
Why it happens: Stone chips compromise paint, water gets behind the inner wing, and the bottom edge collects dirt and moisture.
How to fix it: Replacement front wings are available for all series. It’s a bolt-on panel, so replacement is straightforward. Budget $1,000-2,500 AUD per side including paint.
Severity: Needs attention. Cosmetic but worsens rapidly if ignored.
Engine
XK engine oil leaks
What happens: Oil weeps from cam covers, timing chain cover, sump gasket, and rear main seal. The engine bay is perpetually oily. Oil drips on the exhaust and creates smoke.
Why it happens: The XK engine uses old-style gaskets (cork, paper, and early-type lip seals) that deteriorate with age and heat cycling. The casting surfaces are rough by modern standards, making perfect sealing difficult.
How to fix it: Replace gaskets systematically. Start with the cam covers (easy access, cheap gaskets), then the timing cover, then the sump. The rear main seal requires gearbox removal, do it when the gearbox is out for any other reason. Use modern gasket materials and sealants. Accept that a slight weep is normal, aim for “no drips,” not “factory fresh.”
Severity: Minor annoyance to needs attention. A small weep is cosmetic; rivers of oil indicate neglected seals.
Cooling system inadequacy
What happens: Engine runs hot, particularly in traffic or on warm days. Temperature gauge climbs, coolant may boil over, heater blows hot when it shouldn’t.
Why it happens: The XK engine was designed when cars moved constantly and relied on airflow for cooling. In modern stop-start traffic, the cooling system is marginal. Radiators clog with scale, thermostats fail, water pumps lose efficiency, and fan belts slip. Australian heat makes everything worse.
How to fix it: Comprehensive cooling system service: flush and recore (or replace) the radiator, new thermostat, new water pump if weak, check fan belt tension, and consider an electric fan upgrade. Fresh coolant (50/50 mix, not straight water). Budget $1,000-2,500 AUD for a thorough cooling system overhaul.
Severity: Needs attention. Overheating warps the aluminium head and blows the gasket.
SU carburettor problems (Series 1)
What happens: Rough idle, flat spots, hesitation, black smoke, fuel smell, poor starting.
Why it happens: The twin SU HD6 or HD8 carburettors need regular maintenance, jet needles wear, diaphragms split, float valves stick, and the mixture goes rich or lean. Most mechanics don’t understand SUs and make things worse.
How to fix it: Strip, clean, and rebuild both carburettors. Replace needles, jets, diaphragms, and float valves. Set float heights. Synchronise with a proper flow meter. Budget $400-800 AUD for rebuild kits and a few hours of patient work.
Severity: Needs attention. The car runs badly when the carbs are out of tune, and fuel economy suffers.
Fuel injection issues (Series 2 and 3)
What happens: Hard starting, rough idle, hesitation, stalling, poor economy.
Why it happens: Early Lucas fuel injection (Series 2) is primitive and parts are getting scarce. Later Bosch injection (Series 3) is more reliable but still has age-related issues, injectors clog, sensors drift, wiring degrades, and vacuum lines perish.
How to fix it: Diagnose systematically. Check for vacuum leaks, test the coolant temperature sensor and other inputs, clean or replace injectors, replace perished vacuum hoses. The Bosch system on the Series 3 is well-understood and parts are available. Budget $500-2,000 AUD depending on what’s needed.
Severity: Needs attention. The car is unpleasant to drive with injection faults.
Head gasket failure
What happens: Coolant loss, white smoke from exhaust, overheating, mayonnaise under the oil filler cap.
Why it happens: The aluminium cylinder head expands at a different rate to the iron block. Overheating events, age, and repeated thermal cycling cause the gasket to fail. The XK engine’s long head and six cylinders create a large gasket surface area that’s vulnerable to distortion.
How to fix it: Head off, gasket replaced, head pressure-tested and skimmed if warped. Use quality gaskets and follow the correct torque sequence. Budget $2,000-4,000 AUD.
Severity: Critical. Don’t drive with a failed head gasket, you’ll warp the head and potentially crack the block.
2.8-litre engine problems
What happens: Excessive vibration, bearing failure, overheating, poor performance.
Why it happens: The 2.8 was a de-stroked version of the 4.2 with altered crankshaft and reduced capacity. The shorter stroke created balance issues and increased stress on the bottom end. The engine is also underpowered for the heavy XJ body, leading to over-revving and premature wear.
How to fix it: Swap to a 4.2. Seriously. The 2.8 is a fundamentally compromised engine that’s not worth rebuilding when 4.2 units are plentiful. A 4.2 swap requires a compatible bell housing and some wiring changes but is well-documented.
Severity: Design flaw. The 2.8 is best replaced rather than repaired.
Transmission
Borg-Warner BW66 automatic (early cars)
What happens: Harsh shifts, slipping, delayed engagement. The gearbox overheats under sustained load.
Why it happens: The BW66 is an adequate but uninspired gearbox that doesn’t cope well with age or abuse. Fluid degrades, bands wear, and the torque converter loses efficiency.
How to fix it: Regular fluid and filter changes extend life. When it fails, consider upgrading to a GM TH400, conversion kits are available for all XJ variants. Budget $3,000-5,000 AUD for a TH400 conversion.
Severity: Needs attention. The BW66 is a known weakness.
GM TH400 automatic (later cars), reliable
The TH400 fitted to later Series 2 and all Series 3 cars is one of the most reliable gearboxes ever made. Regular fluid changes are all it needs. If it does develop issues (very rare), rebuilt units are readily available.
Severity: Minimal concern. Change the fluid regularly and forget about it.
Power steering system leaks
What happens: Power steering fluid on the garage floor, heavy steering, groaning from the pump.
Why it happens: Rack seals age and weep. Hose connections corrode. The pump wears internally. Power steering fluid degrades and loses its lubricating properties.
How to fix it: Replace leaking hoses first (cheap, easy). If the rack is leaking, a reconditioned unit is the most cost-effective solution. Replace the pump if it’s noisy. Budget $1,500-3,000 AUD for a comprehensive power steering overhaul.
Severity: Needs attention. The XJ6 is a heavy car and very difficult to steer without power assistance.
Electrical
Lucas ignition failure (Series 1 and 2)
What happens: Misfiring, rough running, hard starting, random stalling. The car runs on five cylinders or fewer.
Why it happens: The Lucas ignition system uses points, condenser, distributor cap, and rotor arm, all of which wear and fail. Moisture gets into the distributor in damp conditions. The condenser fails without warning.
How to fix it: Fit an electronic ignition conversion (Pertronix or similar). It’s the single best modification you can make to a Series 1 or 2 XJ6, better starting, smoother running, more reliable. Costs $200-400 AUD and takes an hour. Keep the original parts as spares.
Severity: Needs attention. Lucas ignition will strand you eventually.
Alternator and charging system failure
What happens: Battery goes flat, warning light stays on, instruments dim at idle, car won’t start.
Why it happens: Early cars had Lucas alternators (or generators on the very earliest models) that fail with age. Voltage regulators burn out. Wiring connections corrode and add resistance.
How to fix it: Test the charging system output. Replace the alternator if output is low. Clean all connections, especially the main battery cables and earth straps. Upgrade to a modern high-output alternator if the original is shot. Budget $300-800 AUD.
Severity: Needs attention. A flat battery strands you and the car is too heavy to push.
Electric window failure
What happens: Windows won’t go up or down, move slowly, or stop halfway.
Why it happens: Window motor brushes wear. Regulators seize or strip. Wiring connections corrode. Switches wear internally.
How to fix it: Diagnose whether it’s the switch, the wiring, or the motor. Replace the failed component. Motors are available (both new and reconditioned). Budget $200-500 per window.
Severity: Minor annoyance, unless the window is stuck down in the rain.
Instrument gauge failures
What happens: Temperature gauge, fuel gauge, or oil pressure gauge reads incorrectly or not at all. Warning lights illuminate randomly.
Why it happens: The Smiths instruments use voltage stabilisers and sender units that fail with age. The printed circuit board behind the instrument cluster develops cracks. Earth connections corrode.
How to fix it: Check the voltage stabiliser first (it regulates the supply to the gauges). Test sender units. Inspect and repair the printed circuit board. Specialist instrument repairers can overhaul the complete cluster. Budget $300-800 AUD.
Severity: Needs attention. A non-functional temperature gauge on any Jaguar is dangerous, you need to know when it’s running hot.
Central locking and door lock failures
What happens: Central locking won’t operate, or works on some doors but not others. Key won’t turn in the door lock.
Why it happens: Vacuum-operated actuators (Series 2 and 3) fail when diaphragms split or vacuum lines perish. Lock barrels wear. Microswitches fail.
How to fix it: Check the vacuum supply first. Replace perished vacuum lines. Replace failed actuators. Rebuild or replace worn lock barrels. Budget $200-600 for a complete central locking overhaul.
Severity: Minor annoyance. Manual locking still works.
Suspension and Steering
Front suspension bush wear
What happens: Clonking over bumps, vague steering, uneven tyre wear, the car wanders at motorway speed.
Why it happens: The double-wishbone front suspension uses rubber bushes that harden and crack with age. Ball joints wear. Anti-roll bar links deteriorate.
How to fix it: Replace all bushes, ball joints, and anti-roll bar links. Polyurethane bushes are available as an upgrade. A complete front suspension refresh runs $800-2,000 AUD in parts, plus labour.
Severity: Needs attention. Worn front suspension affects handling and tyre wear.
Rear suspension compliance mount failure
What happens: Vague rear end, clunking, rear tyre wear. The back of the car feels disconnected from the front.
Why it happens: The independent rear suspension uses large rubber compliance mounts (cages) that deteriorate with age. They’re critical to maintaining correct rear geometry.
How to fix it: Replace the compliance mounts. It’s a significant job involving rear subframe work. Budget $1,500-3,000 AUD.
Severity: Needs attention. Failed mounts affect handling, tyre wear, and ride quality.
Steering rack wear and leaks
What happens: Play in the steering, vague centre feel, clonking on turn, power steering fluid leaks.
Why it happens: The rack and pinion wears over high mileages. Power steering seals fail. Mounting bushes deteriorate.
How to fix it: Reconditioned racks are available and are the most cost-effective solution. Replace mounting bushes at the same time. Budget $1,500-3,000 AUD.
Severity: Needs attention. Excessive play makes the car feel sloppy and is a roadworthy failure.
Damper (shock absorber) deterioration
What happens: Wallowing ride, excessive body roll, the car fails to settle over bumps, uneven tyre wear.
Why it happens: Dampers lose their effectiveness over time. The XJ6’s relatively soft suspension relies heavily on good dampers to control body motion.
How to fix it: Replace all four dampers. Aftermarket options (Bilstein, Koni) are often better than the originals. Budget $800-1,500 AUD for a set of quality dampers.
Severity: Needs attention. Bad dampers spoil the XJ6’s legendary ride quality and compromise handling.
Brakes
Brake servo failure
What happens: Very hard brake pedal, poor stopping performance. The car feels like it has no brakes.
Why it happens: The vacuum servo diaphragm fails, the check valve sticks, or vacuum lines leak.
How to fix it: Test the servo by pressing the brake pedal with the engine off, then starting the engine, the pedal should drop slightly. If it doesn’t, the servo is faulty. Rebuild or replace. Reconditioned servos are available. Budget $500-1,000 AUD.
Severity: Urgent. The XJ6 is a heavy car and needs servo assistance to stop safely.
Caliper seizure
What happens: Uneven braking, pulling to one side, excessive heat from one wheel, brake drag.
Why it happens: Brake caliper pistons seize from corrosion, especially if the car has been sitting for extended periods. Old brake fluid absorbs moisture, which accelerates internal corrosion.
How to fix it: Rebuild or replace the affected caliper. Replace all brake fluid with fresh DOT 4 or DOT 5.1. Inspect all calipers, if one has seized, the others are likely close behind. Budget $300-600 per caliper.
Severity: Needs attention. A seized caliper is a safety hazard.
Brake disc warping
What happens: Judder through the steering wheel or brake pedal under braking.
Why it happens: Discs warp from heat, particularly if the brakes are used hard then the car is stopped (heat concentrates at the pad contact point). Age and corrosion compound the problem.
How to fix it: Machine the discs if they’re within thickness limits. Replace if they’re too thin or cracked. Budget $200-500 per axle including pads.
Severity: Needs attention. Warped discs reduce braking effectiveness and are unpleasant to drive with.
Climate Control
Air conditioning system failure
What happens: A/C doesn’t cool, compressor won’t engage, strange noises from under the bonnet.
Why it happens: The A/C system is complex and every component degrades with age, compressor seals leak, condensers corrode, evaporators fail, and the control system (vacuum-operated flaps on many XJ6 models) deteriorates. Early systems used R12 refrigerant, which requires conversion to R134a.
How to fix it: Full A/C system diagnosis and overhaul. Retrofit to R134a if still on R12. Replace failed components. Budget $2,000-5,000 AUD for a comprehensive A/C restoration.
Severity: Essential for Australian ownership. A non-functional A/C in an XJ6 during summer makes the car unusable.
Heater matrix leak
What happens: Coolant smell in the cabin, damp carpet on the passenger side, fogged windscreen. Coolant level drops with no external leak.
Why it happens: The heater matrix, a small radiator inside the dashboard, corrodes and develops leaks. Old coolant or running plain water accelerates the corrosion.
How to fix it: Replace the heater matrix. Unfortunately, this usually requires significant dashboard disassembly. Budget $500-1,500 AUD including labour. Run proper coolant mix after replacement.
Severity: Needs attention. Coolant in the cabin rots the floor and the vapour isn’t healthy to breathe.
Summary
The XJ6’s problems are the problems of any complex luxury car from this era. Rust is the existential threat, electrics are the daily frustration, and deferred maintenance is the hidden cost that turns a bargain purchase into an expensive lesson.
The key to happy XJ6 ownership is buying well (body condition above all else), maintaining regularly (find a specialist and stick with them), and addressing issues promptly rather than waiting for them to escalate. A well-maintained XJ6 is not an unreliable car, it’s a car that needs care and rewards it with an experience that nothing else in its price range can match.
The Series 3 with Bosch ignition is the most reliable variant. The 4.2 XK engine is robust and well-supported with parts. The GM TH400 automatic is virtually indestructible. Focus on keeping the body solid, the cooling system healthy, and the electrics clean, and an XJ6 will serve you well for years.
Loading comments...