The six cylinder Series 3

The part that is well evidenced

A 4.2 litre Series 3 was catalogued. Motor's Series 3 launch issue of 3 April 1971 shows the XK 4.2 powered version on the price lists, with the V12 costing £286 more, a premium of about 10 per cent. That is a price list citation to a named period publication with a date, and it is the strongest single piece of evidence on this page. The archive has it at second hand and should obtain the issue itself.

So the model existed as an offering. Whether it existed as a car is a separate question.

The part that is not evidenced

The Jaguar Daimler Heritage Trust's own published numbering reference, Research Guide 001F, issue 3 of January 2023, lists Series 3 only as Series 3 V12, with engine prefix 7S and chassis prefix 1S. No six cylinder Series 3 engine, chassis prefix or chassis range appears anywhere in it. That is a significant negative from a factory source: whatever these cars were, the Trust's public numbering reference does not recognise them as a Series 3 variant.

The figure everyone repeats is two or three cars, attributed to the Heritage Trust. The attribution is traceable, and it leads to a forum thread whose sole support is a quotation from a tweet by a Trust account. No document, brochure, build ledger extract, photograph or specification sheet appears anywhere in that thread. The archive could not find the tweet. A social media post is not a document, and it sits awkwardly beside the Trust's own published guide, which lists no such model.

Other figures circulate with no more support. One respected history site says only three were manufactured, without citation. Another writer's own view is that the specification never existed other than on price lists, with the assertion that a few were made attributed to a colleague in a footnote.

The EX cars

The Jaguar Enthusiasts Club published an account in August 2017 of an inspection of a car at a garage in Cheshire, claimed to be one of the development cars produced ahead of the Series 3 launch. The club deserves credit for recording its own scepticism in print: both inspectors were, in their words, a little sceptical, because there have been so many stories about so called rare or unique cars, particularly with E-Type prices continuing to rise.

Their scepticism was reduced by seeing the car. It is worth being clear about what that is and is not. It is a reaction to condition and to physical features, such as the six cylinder engine appearing to sit a little higher than normal, unusual engine mounts, and square headed blanking plugs beside the spark plugs. It is not a documentary authentication. The article gives neither a chassis number nor a registration for the car.

The club's reasoning about how many there were is worth examining. It rejects a car claimed as EX104 on the grounds that if the cars started at EX100 then EX104 would make five, which is one too many. That reasoning depends on a prior belief that there were four, and the club does not say where that belief comes from. Without a source for it, the argument is circular.

A distinction that may explain the confusion

The club's account does not separate two quite different propositions: a Series 3 sold with a six cylinder engine, and a six cylinder car used as a Series 3 development hack.

The records for these cars point at the second. EX102 is described as carrying V12 suspension, brakes, radiator, widened rear arches and a V12 bonnet. EX100 is recorded as a car that began as a Series 2 and was reconstructed by Jaguar as a V12 Series 3, and was later bought by a factory development engineer who raced it and won the 1974 British Production Sports Car Championship.

If the EX cars are V12 development mules built on six cylinder shells, that is a materially different thing from six cylinder Series 3 production cars, and a good deal of the confusion in the literature may follow from running the two together. The archive offers that as an observation rather than a finding.

The records themselves disagree, which does not help. The club says EX100 was fitted with a V12 by a private owner for racing; xkedata says Jaguar reconstructed it. The club says EX101 is Willow Green; xkedata records it as light blue in 1969 and dark blue in 2017. The xkedata record for EX102 is internally inconsistent, giving both right and left hand drive and quoting an engine capacity that is neither a 3.8 nor a 4.2. There is no xkedata record for EX103 or EX104 at all.

Where this leaves it

A 4.2 Series 3 was catalogued and priced in April 1971. Beyond that, the honest position is that the number built is not established at any tier, that no evidence of a customer delivery has been found, and that the most commonly repeated figure rests on a forum report of a tweet.

Three things would settle much of it: the Motor issue of 3 April 1971, read directly; the November 2017 auction result for the car the club inspected, including whatever chassis number the auctioneer quoted; and any Heritage Certificate for a car of this description. The archive would be glad of any of them.