Common mechanical faults

This page collects the faults owners actually meet, organised by system. It is a survey, not a workshop manual: for each item it says what fails, why, and what the sensible response is. Nothing here is a reason not to own the car. Almost all of it is a reason to maintain it on schedule rather than on breakdown.

Cooling

Cooling is the system's fault with the loudest reputation and the most mundane causes. The standard culprits are a silted or tired radiator, failed electric fan motors, perished hoses, a sticking thermostat and ignition or mixture settings that make the engine work hotter than it should. Sort the whole system together rather than one part at a time, because each marginal component adds its share. On the Series 3 V12 the margin is narrower and the consequences of overheating more expensive, which the six versus V12 page covers in more detail.

Oil leaks

The XK engine weeps. The rope-type rear crankshaft seal and the gasketing of the period mean a dry 3.8 or 4.2 is the exception rather than the rule, and a light weep is a characteristic to monitor rather than a fault to chase. Leaks worth acting on are the ones that reach the exhaust, the clutch or the ground in quantity. Modern lip-seal conversions for the rear crank exist and are widely fitted at rebuild time.

Timing gear and top end

The XK's timing chains, guides and tensioners are wear items with a long life and a noisy end. A rattle at start-up that settles, or a persistent rattle from the front of the engine, points here, and the job is straightforward for anyone who knows the engine. Valve clearances on the XK are set with shims and are checked as routine maintenance, not ignored until the engine goes quiet, because quiet means tight, and tight means burned valves in time.

Carburettors and fuel

Six-cylinder cars run triple SU or, on later Series 2 cars, twin Zenith-Stromberg carburettors. The SUs are simple, durable and tolerant, and most complaints trace to worn throttle spindles, perished diaphragms on the Strombergs, or synchronisation that has drifted. Modern ethanol-blended fuel attacks old rubber and can affect float needles and seals, so fuel system rubber of unknown age deserves replacement as a matter of course. The XK engine page covers the carburettor differences between the series.

Electrics

The electrics are conventional and mostly Lucas, and the faults are conventional too: corroded earths, tired connections and old switches rather than design flaws. The earths deserve first attention whenever something behaves oddly, because a poor earth makes good components look faulty. Check the cooling fans work, since a car whose fans have quietly failed is a car waiting to overheat in its first traffic jam.

Brakes and the rear axle

The brakes are discs all round, with the rears mounted inboard beside the differential. Inboard brakes reduce unsprung weight and are laborious to reach, so rear brake work has a reputation for cost that is really a reputation for access. Leaking differential output seals will oil the rear discs, which is the classic combined fault. Handbrake mechanisms on the inboard setup suffer from neglect. None of this is difficult, it is simply slow, and a specialist charges for the hours.

Gearbox and driveline

The early Moss box is slow and has no synchromesh on first, which is how it was made. Faults are jumping out of gear, noise and a change that deteriorates. The later all-synchromesh box is tougher in use. Either way, the differential, universal joints and the splined hubs on wire-wheeled cars are wear items. Worn wheel splines announce themselves with a click on drive and overrun, and they do not improve with neglect.

Common questions