Jaguar XK120, XK140 and XK150 (1948 to 1961)

Why people buy one

• The XK120 introduced the XK engine and was among the fastest production cars of its day.
• The engine is durable when serviced, and the gearbox, axle and chassis are tough.
• A wide choice: the pure XK120, the XK140 with rack-and-pinion steering and small rear seats in closed cars, and the XK150 with disc brakes and a one-piece windscreen.
• Factory records survive, and the Jaguar Daimler Heritage Trust issues certificates showing original build details.
• Strong club support and a large specialist network, with most mechanical parts available.

What to weigh up

• Most XKs were exported, so factory right-hand-drive cars are scarcer, especially the XK140 roadster (only 73 right-hand-drive cars), and some UK cars are converted left-hand-drive cars; any conversion should be declared.
• Motor Sport warned that some cars offered for sale are not what they claim, and that faking an XK is easier than it sounds. Only the earliest XK120 roadsters, a few hundred cars, had aluminium bodies (sources give figures from 200 to 242), and new aluminium bodies are made, so a claimed "alloy" car needs its chassis number checked.
• Many cars have been rebuilt to indifferent standards, and Motor Sport doubted claims of "rust-free" cars.
• SE and S specifications, engine sizes and body styles are easy to claim, so check the build record rather than badges.
• The Moss gearbox has no synchromesh on first, new parts are scarce, and five-speed conversions are common.
• Drum brakes on the XK120 and XK140 are weak by modern standards, which is why many cars now have disc brake conversions.

Where they rust

• Sills and rear chassis extensions; poor door gaps can be a sign of rot here.
• Front valance and the headlamp and sidelamp housings, which trap water and rot the wing around them.
• Trailing edges of the front wings and the joint between the A-post and scuttle.
• Rear wing mounting points and the beading between the rear wings and the rear body.
• Door hinge boxes; early doors have timber frames with aluminium skins, and rot lets heavy doors drop.
• Front suspension mountings, anti-roll bar mountings and rear chassis rails.
• Lower panels and inner and outer rear panels, especially on the XK150.
• Lead filler on older repairs can hide rust in the steel beneath.

Mechanical weak spots

• Engine: some blue smoke is normal, but look for heavy smoke and oil leaks; aim for about 40psi of oil pressure when warm at cruising revs. A rattling timing chain or noisy water pump needs attention.
• A leaking rear crankshaft seal means taking the engine out, and overheating is a common complaint.
• Gearbox: the Moss box is durable but slow; excessive first-gear whine means a rebuild, and overdrive (XK140 and XK150 option) is sensitive to oil level and solenoid adjustment.
• Steering: the XK120 has a steering box, costly to rebuild if worn, while the XK140 and XK150 use rack-and-pinion.
• Suspension: check front bushes and ball joints, and the XK120's lever-arm rear dampers for leaks.
• Brakes: drums on the XK120 and XK140, which seize on little-used cars; Dunlop discs on the XK150. Many earlier cars have front disc conversions.
• Electrics are simple; faults are usually corrosion or loose connections, and many cars have been converted from twin 6-volt batteries to a single 12-volt battery and alternator.

At a Mathewsons viewing

• Check the chassis, engine, gearbox and body numbers against the V5C, and ask for a Jaguar Daimler Heritage Trust certificate to compare with the original engine number, colour and market; the Trust does not inspect cars, so the certificate does not prove the car is genuine.
• On a claimed alloy XK120, SE, S or factory right-hand-drive car, ask a club register or XK specialist to check the chassis number before bidding.
• Look along the body for panel fit, door drop and bubbling where steel meets aluminium, and lift the doors on their hinges.
• With a torch, look under the car at the sills, rear chassis extensions, front suspension mountings and the wing mounting points, and look for fresh underseal or filler.
• Open the bonnet and look for oil leaks and coolant stains, and if staff start the car, listen for timing chain rattle and watch the oil pressure; do not assume it will be started.

Parts, specialists and clubs

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Sources

• Buyers' guide: Jaguar XK120, 140, 150 (Motor Sport), February 1996
• 1948 to 1961 Jaguar XK120, XK140 and XK150 buying guide (Magneto), 8 July 2025
• Jaguar XK120 buying guide (Drive-My), 9 August 2015
• Living with a Jaguar XK150 (Prestige & Performance Car), accessed 14 October 2026
• Tech tips: Jaguar XK120, XK140 and XK150 (Classic Motorsports), accessed 14 October 2026
• 1950 Jaguar XK120 Alloy Roadster, lot description (RM Sotheby's), accessed 14 October 2026
• Certificates (Jaguar Daimler Heritage Trust), accessed 14 October 2026
• Jaguar XK140 (Wikipedia, citing Jaguar Heritage Trust figures), accessed 14 October 2026