Jaguar XK120, XK140 and XK150 buyer's guide

The Jaguar XK120 was revealed at the London Motor Show at Earls Court in 1948 as a showcase for Jaguar's new twin-cam XK six-cylinder engine. It was developed into the XK140 in late 1954 and the XK150 in 1957, and the family gave way to the E-Type in 1961. Around 30,000 were built across the three models, as open two-seaters (roadsters), drophead coupes and fixed head coupes.

People buy them for the shape, the XK engine, the period motorsport history and a driving experience that feels very different from the later E-Type: a separate chassis, a tall gearbox and a lot of mechanical character. Most were exported, most have been restored at least once, and the gap between a well-built car and a tired or poorly rebuilt one is large, so structure, identity and history matter far more than paint.

This guide is for joncosson.com readers buying at a dealer, privately or at an auction such as Mathewsons in North Yorkshire, and for owners preparing to sell. It is not a repair manual.

By Jon Cosson · Checked 20 October 2026

At a glance

Built	XK120 1948 to 1954, XK140 1954 to 1957, XK150 1957 to late 1960 (sold into 1961)
Numbers made	About 12,000 XK120s, just under 9,000 XK140s and about 9,400 XK150s
Body styles	Open two-seater (roadster), fixed head coupe (XK120 from 1951), drophead coupe (XK120 from 1953)
Construction	Separate steel box-section chassis with a body of steel, aluminium and, in places, timber framing
Early alloy cars	About 240 XK120s with hand-built aluminium bodies over ash frames, late 1948 to spring 1950
Engines	XK twin-cam straight six: 3.4 litres throughout, plus 3.8 litres in the XK150 from October 1959
Gearbox	Four-speed Moss manual without synchromesh on first; overdrive optional on XK140 and XK150; automatic option from 1956
Brakes	Drums all round on XK120 and XK140; Dunlop discs all round on the XK150
Maker and factory	Jaguar Cars, Coventry
Clubs	Jaguar Enthusiasts' Club, Jaguar Drivers' Club

The Jaguar XK120, XK140 and XK150 in brief

The XK120 used a shortened and narrowed version of the Jaguar Mark V saloon chassis, with independent front suspension by wishbones and torsion bars and a live rear axle on leaf springs. The 3.4-litre XK engine gave 160bhp on twin SU carburettors. Jaguar originally planned a small run of hand-built cars, but demand was such that the roadster went into series production. The first cars, roughly 240 of them, had aluminium bodies on ash frames; from spring 1950 the body was pressed steel, though doors, bonnet and boot lid stayed aluminium.

A fixed head coupe joined the roadster in 1951 and a drophead coupe in 1953, both with wind-up windows and a walnut dashboard. From 1951 a Special Equipment package added higher lift camshafts, twin exhausts and wire wheels for about 180bhp. All XK120s have drum brakes and the Moss four-speed gearbox.

The XK140 arrived in late 1954 with heavier bumpers, a cast grille, more cabin space from moving the engine and bulkhead forward, rack and pinion steering and telescopic rear dampers. Power rose to 190bhp, or 210bhp with the C-type head. Overdrive became optional and, from 1956, an automatic. Brakes were still drums.

The XK150 launched in May 1957 as a fixed head and drophead coupe, with a one-piece windscreen, a higher wing line and Dunlop disc brakes all round. The roadster followed in March 1958. The triple carburettor 3.4 S gave 250bhp, and the 3.8-litre engine arrived in October 1959, reaching 265bhp as a 3.8 S. Production ended in late 1960, ahead of the E-Type's launch in March 1961.

More than three quarters of all XKs went overseas, mainly to North America, so factory right-hand drive cars are a minority: only 73 right-hand drive XK140 roadsters were built, for example. Many UK cars came back from the US and elsewhere, and a good number have been converted to right-hand drive. Establish that history first on any car.

Versions to know

Version	Years	What to know
XK120 alloy roadster	1948 to 1950	About 240 cars with aluminium bodies over ash frames, the most collectable of the family. Confirm alloy status from the chassis number and Heritage record.
XK120 steel roadster	1950 to 1954	Pressed steel body with aluminium doors, bonnet and boot lid, sidescreens and a light hood. Mostly left-hand drive.
XK120 fixed head coupe	1951 to 1954	Steel roof, wind-up windows, walnut dashboard. Only about 195 were right-hand drive.
XK120 drophead coupe	1953 to 1954	Trimmed folding hood, wind-up windows and walnut dashboard.
XK120 Special Equipment (SE)	1951 to 1954	Higher lift cams, twin exhausts and wire wheels for about 180bhp. Confirm SE status from the factory record, not the parts fitted today.
XK140 roadster, FHC and DHC	1954 to 1957	190bhp, rack and pinion steering, telescopic dampers and more room. Overdrive optional, automatic from 1956.
XK140 SE (MC in North America)	1954 to 1957	C-type head for 210bhp, twin exhausts and wire wheels. The record decides whether a car is a true SE.
XK150 FHC and DHC	1957 to 1960	One-piece windscreen, wider body, disc brakes all round. The fixed head is the most numerous XK150.
XK150 roadster	1958 to 1960	Wind-up windows; launched first for export, so right-hand drive cars are scarce.
XK150 S (3.4 S and 3.8 S)	1958 to 1960	Triple SU carburettors, 250bhp as a 3.4 and 265bhp as a 3.8. The most powerful and rarest XK150s.

Pros and cons

Pros	Cons
The XK engine is robust and well understood, and every specialist knows it. Three body styles and several engine tunes give a wide choice, from spartan roadster to comfortable coupe. A separate chassis means the structure can be assessed and repaired in a way a monocoque often cannot. Jaguar Heritage Trust records can confirm the original colour, trim, build date and destination of every car. Strong club, specialist and parts support in the UK and abroad. Disc braked XK150s and well sorted XK140s are usable on modern roads.	Rust can be widespread in the chassis, body and door pillars, and bodywork is costly because the cars were largely hand finished. Timber framing in doors and body sections of coupes and early cars can rot unseen. The Moss gearbox is slow, has no synchromesh on first, and rebuild parts are scarce. XK120 and XK140 drum brakes need regular adjustment and fade under hard use. Most cars are left-hand drive or converted to right-hand drive, which affects originality. Many cars carry later engines, gearboxes or upgrades, so a truly original car is hard to find.

Pros

Cons

The XK engine is robust and well understood, and every specialist knows it.
Three body styles and several engine tunes give a wide choice, from spartan roadster to comfortable coupe.
A separate chassis means the structure can be assessed and repaired in a way a monocoque often cannot.
Jaguar Heritage Trust records can confirm the original colour, trim, build date and destination of every car.
Strong club, specialist and parts support in the UK and abroad.
Disc braked XK150s and well sorted XK140s are usable on modern roads.

Rust can be widespread in the chassis, body and door pillars, and bodywork is costly because the cars were largely hand finished.
Timber framing in doors and body sections of coupes and early cars can rot unseen.
The Moss gearbox is slow, has no synchromesh on first, and rebuild parts are scarce.
XK120 and XK140 drum brakes need regular adjustment and fade under hard use.
Most cars are left-hand drive or converted to right-hand drive, which affects originality.
Many cars carry later engines, gearboxes or upgrades, so a truly original car is hard to find.

Myths and realities

A 'rust free' car from a dry US state needs no structural checks.

Dry climates help, but cars still rust in the sills, pillars and chassis, and conversion work after import varies widely.

An XK120 that looks like an alloy car is an alloy car.

Steel XK120s already had aluminium doors, bonnet and boot lid, so a magnet on those panels proves nothing. Only the chassis number and the factory record confirm one of the roughly 240 alloy cars.

Matching numbers means the car is original.

Numbers are only part of originality; body, colour, trim and steering side matter too. A Heritage certificate records what the factory built, not what you are looking at.

What to check

Chassis and body structure

The chassis is massive but not immune, and the body panels, sills and pillars hide much of what matters. Start here and allow plenty of time with a torch and a magnet.

Chassis rails along their full length, especially the rear extensions behind the axle, for rust, old repairs, kinks or crash damage.
The chassis around the front suspension mountings and torsion bar anchorages for corrosion or heavy welding.
Sills and the joint between sill and body; poor door gaps often point to rot or collapse here.
Door pillars (A and B posts) and the rear box sections, which trap water and are a known rust area.
Front wings around the headlamp bowls and sidelight housings, where water collects and rots the panel from inside.
Rear wings, wheel arches and the area where the rear wings bolt to the body.
Doors that drop when lifted on their hinges, rub, or need slamming, which suggests worn hinges, rotten pillars or timber.
Uneven panel gaps, especially wing to door; bodies were hand fitted so no two cars match, but poor gaps can signal a rushed restoration.

Aluminium bodies and timber framing

Early XK120s used aluminium over ash, and timber also appears in the doors and body of the coupes. Wood rots quietly behind trim and paint.

On an alloy XK120, ask for photographs or invoices showing the condition or replacement of the ash frame.
Corrosion of aluminium where it meets steel fittings, showing as blistered paint or white powder along edges.
Aluminium doors, bonnet and boot lid on all XK120s for splits around hinges and dents hidden by filler.
Door frames on coupes and early cars: soft timber lets doors sag and drift out of line.
Drophead coupe hood frame and the rails it mounts to; check the hood folds and seals properly.
Damp carpets, water stains or a musty smell, all signs that leaks are reaching timber.

Engine

The XK six is durable, but most engines have been rebuilt and many cars have a later or replacement unit. Check condition and identity together.

Engine number stamped on the block and cylinder head against the V5C, the catalogue or advert, and the Heritage certificate.
Cold start: rattle from the timing chains that does not settle, and noisy valve gear.
Oil pressure when hot; it should stay healthy at speed, with a drop at tickover being normal. Ask a specialist for the expected figure for that engine.
Blue smoke on the overrun or under load, and oil leaks, particularly from the rear main seal and head gasket.
Mayonnaise under the oil filler cap or oil in the coolant.
Temperature after idling in traffic; overheating is a common complaint, and many cars now have an electric fan or alloy radiator, which is generally accepted.

Gearbox and drivetrain

All three models use the Moss four-speed box unless it has been changed. Know what should be fitted before you drive.

First gear has no synchromesh; check that first and reverse select cleanly at rest.
Second gear synchromesh is often worn, so changes need double declutching; crunching on fast changes is common.
Overdrive on XK140 and XK150: confirm it engages and disengages promptly; units are sensitive to oil level and solenoid adjustment.
Automatics on XK140 and XK150: smooth changes, no slip, and clean fluid.
Five-speed conversions are popular; ask what unit is fitted, who fitted it, and whether the original box comes with the car.
Clutch slip or judder, and clonks from the propshaft universal joints or rear axle.

Suspension, steering and brakes

Drum brakes, a steering box and lever arm dampers make the XK120 the most demanding to drive. Know which arrangement the car should have.

XK120 and XK140 drums: even braking with no pull, and a pedal that stays firm; the drums need correct adjustment and fade under hard use.
XK150 discs: pull, judder or noise, and check the handbrake holds.
Disc brake conversions on earlier cars: who fitted the kit and whether the original parts are kept.
XK120 steering box: excess play at the wheel, which is expensive to put right; rack and pinion conversions require chassis work and should be documented.
XK120 rear lever arm dampers for leaks; XK140 and XK150 telescopic dampers for leaks and bounce.
Front ball joints, bushes and kingpin wear, shown by knocks, wander or uneven tyre wear.
Wire wheels for loose spokes, worn splines and correct spinners.

Electrics and instruments

Lucas electrics are simple, but original wiring is now very old and many cars have been partly modernised.

All lights, indicators, wipers and horns working.
Charging shown at the ammeter or warning light.
Oil pressure, temperature and fuel gauges, rev counter and speedometer working.
Wiring behind the dashboard and under the bonnet for brittle insulation, scorching or amateur joins.
Electronic ignition, electric fuel pump and fan conversions: fine on a driver, worth noting on a concours car.

Interior and trim

Retrimming is straightforward but not cheap, and a few original items are hard to replace.

Leather seats for splits and worn bolsters, and correct style for the model.
Walnut dashboard and door cappings on coupes for lifting veneer, cracks and water damage.
Hood fabric, frame, seals and sidescreens on roadsters; poor fitting lets water into the timber and floor.
Original switches, badges and instruments, which are harder to find than carpets or seat covers.
The colour and trim combination against the Heritage certificate.

Paperwork and originality

With so many cars rebuilt, imported or converted, the paperwork decides what the car really is.

Chassis number on the plate and frame against the V5C; the number series indicates the model, body style and original steering side.
Engine, body and gearbox numbers recorded and compared with the Heritage certificate; a car with all of these matching is uncommon.
Jaguar Heritage certificate showing build and dispatch dates, original colour and trim, destination and first registration where recorded.
Import history: when the car came to the UK, how it was registered, and whether its age-related or original registration is correct.
Right-hand drive conversions: who did the work, when, and whether the record shows the car was built left-hand drive.
SE, S, alloy or other special status confirmed by the factory record, not just by the parts fitted.
Restoration invoices and photographs, especially of the chassis, timber and structure before painting.

On the test drive

Start from cold if you can, listening for timing chain rattle and watching for smoke and oil pressure as it warms.
Pull away in first and change up through the box, double declutching into second if needed; note any baulking or crunching.
Try overdrive if fitted, checking it engages and releases cleanly.
Brake firmly from speed in a safe place: the car should stop straight; on drum cars expect more effort and plan ahead.
Feel for steering play and wander, especially on an XK120 with its steering box.
Watch the temperature gauge in slow traffic and check the fan cuts in.

Buying at auction

XKs are regular entries at UK auctions such as Mathewsons. Viewing is your one chance to inspect, so bring a torch, magnet and notebook, and treat the catalogue as the seller's description, not an independent report.

What you can check in viewing week

Use a torch to look under the sills, along the chassis rails and at the rear frame extensions, front suspension mounts and door pillars.
Use a magnet on the steel lower wings and sills to find heavy filler, bearing in mind the aluminium panels.
Lift each door on its hinges and open and close it to check for sagging pillars or timber.
Read the chassis plate and engine number and compare them with the V5C and the catalogue.
Look at the Heritage certificate and history file if offered, and check colour, trim and steering side against it.
Check oil and coolant levels and condition and look for leaks under the car.
Listen to a start-up if the auction house allows it, watching for smoke and oil pressure.

What you usually cannot do

You usually cannot drive the car, so gearbox, overdrive, brakes and steering are untested.
You usually cannot put it on a lift, so the full chassis and floors are only partly visible.
You cannot see timber framing behind trim or ash frames under alloy panels.

Tips

Read the catalogue closely: words such as 'believed', 'reported' or 'understood to be' mean unverified. Note whether it says matching numbers, factory right-hand drive or SE, and whether evidence is offered.
Set your limit before the day, including the buyer's premium and any VAT on the premium, and stick to it.
Factor in the work you found during viewing and assume more is hidden.
Arrange transport home in advance; an enclosed trailer or transporter is safer than driving an unknown car a long way.

What makes one more desirable

Originality and documented identity: matching numbers backed by a Heritage certificate and a clear history.
Factory right-hand drive, which is rare in every model and very rare in some body styles.
Early alloy bodied XK120s, which are the most sought after of the family.
Higher performance versions such as SE, XK150 S and 3.8 S, confirmed by the factory record.
Body style: roadsters and drophead coupes are generally more sought after than fixed head coupes, though the coupes are often the more practical cars.
Quality and documentation of restoration, particularly of the chassis, timber and panel fit.

This guide does not give values or predict prices.

Selling a Jaguar XK120, XK140 and XK150

XK buyers are usually well informed, so a documented car with an honest description sells more easily than a shiny one with gaps in its story.

Preparing the car

Clean the car thoroughly, including underneath, so the chassis and structure can be seen.
Fix small faults such as lights, gauges and leaks that make buyers wonder what else has been neglected.
Check fluids and tyres, and make sure the car starts readily from cold.
Gather any original parts removed during upgrades, such as a Moss gearbox, drum brakes or a steering box.

Paperwork

V5C in your name with the correct chassis and engine numbers.
Jaguar Heritage certificate, or order one before listing.
Restoration invoices and photographs, especially of the chassis and timber.
Import and conversion records, including when and by whom any right-hand drive conversion was done.

Where to sell

Classic car auctions such as Mathewsons, which bring a wide audience; check the seller's fees and entry terms.
Specialist Jaguar dealers, on a sale or return basis or outright.
Club magazines and websites of the Jaguar Enthusiasts' Club and Jaguar Drivers' Club.

Writing the description

State the model, body style, engine size and tune, steering side and whether it is factory or converted.
Say clearly which numbers match and what the Heritage certificate shows.
List modifications such as disc brakes, five-speed gearbox, electric fan or power steering, and whether originals are included.
Describe the restoration: when, by whom and what was done, with photographs.

Living with one

Parts supply is good for mechanical items, body panels and trim, with several UK and overseas specialists, though some switches, hood frames and Moss gearbox internals are scarce.
XK specialists cover servicing, bodywork and restoration, and a specialist inspection before buying is worthwhile.
The fixed and drophead coupes are the most comfortable for longer trips; the roadsters are fair weather cars, and tall drivers may find the XK120 cramped.
In the UK, cars over 40 years old can be registered as historic vehicles, exempt from road tax and, in most cases, MOT, though they must still be kept roadworthy.
Agreed value classic insurance with limited mileage is widely available.
The Jaguar Enthusiasts' Club and Jaguar Drivers' Club offer technical advice, events and contacts.

Clubs and registers

Questions people ask

Which is the best XK to buy: XK120, XK140 or XK150?

The XK120 is the purest but most demanding to drive, with drum brakes and a steering box. The XK140 adds rack and pinion steering and more room. The XK150 has disc brakes and the most comfortable cabin, so it is the easiest to use regularly.

How many aluminium XK120s were made?

About 240 roadsters had aluminium bodies over ash frames, built between late 1948 and spring 1950; figures up to 242 are quoted depending on how specially bodied chassis are counted. Confirm any claimed alloy car through the Jaguar Heritage record.

What rusts on a Jaguar XK?

Sills, chassis rails and rear frame extensions, door pillars, rear box sections, wheel arches and the front wings around the headlamps and sidelights. Timber in coupe and early car doors can rot too.

What does matching numbers mean on an XK?

It usually means the engine and chassis numbers, and ideally body and gearbox numbers too, agree with the factory record. A Jaguar Heritage certificate lists what the car left the factory with, but it does not confirm the identity or condition of the car in front of you.

Is a left-hand drive conversion a problem?

Most XKs were built left-hand drive, so many UK cars are converted. A good conversion is usable, but factory right-hand drive cars are generally more sought after, and a converted car should be described as such.

Is the Moss gearbox hard to live with?

It is slow, first gear has no synchromesh and second is often worn, so it rewards patience and double declutching. It is generally durable, but rebuild parts are scarce. Many owners fit five-speed conversions for easier driving.

Sources

Checked 20 October 2026.

An independent guide. Not a valuation and not financial advice. Always inspect a car in person or have it inspected before you buy.