XK120 radiator rebuild

For what is worth: my XK120 is definitely cold-blooded. I bought it without thermostat and it would not go above 50 and it was slow at it. It is much faster on warm up now, and keeps a nice 70° temp. Aluminium radiator was more of a precaution for trips to Spain (yes I think I will…)

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Yours is freshly restored as I recall, where mine at the time was run down and neglected, so possibly that is one factor among many. It was a long time ago, before the internet, and it took me 8 or 10 years to find the right thermostat. Anyway just saying it can be done if necessity demands.

Hi all,

I replaced the radiator cap with a new (round style) one, and refilled (1.5 gallons of coolant down!) - definitely has improved things, I didn’t go as far as on the first run. I think I’ll try the overflow-tank addition @Rob_Reilly mentioned as well…


the correct sleeve bellows thermostats can be found, new old stock on ebay from time to time…Moss Classic Gold has one now that is correct (may need a tiny bit of “file dressing” on the top flange. See my article on Thermostats for the XK120…for the numbers and types of the correct ones…must have sleeve and bellows. Stat specs run from 68, many in the 70s and so me Winter stats that are in the high 80s…so look for that in any NOS on ebay. I bought several a few years ago…low price 45 USD…most in the $55 yo 65…some up to 90, The new Moss Classic Gold just over $100. Good time to fit the proper hoses…the bypass hose is an odd one…as a different size at each end. Top hose with 3 ribs…easy to fit. Bottom hose a lot of foul language, skinned knuckles.

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Hi John,
I also drive my coupe through the winter as much as the New England weather conditions allow. Dry roads with no salt or sand is the requirement. Yesterday I just changed my winter 86 C (187 F) thermostat to a 74 C (165 F) summer thermostat. The winter thermostat allows the engine to provide decent heat to the cab and makes it quite comfortable for November through April driving. The summer thermostat lets the car run much cooler so no fear of overheating in 95 F summer heat or traffic.

My radiator was also recored with a Maine Radiator core, with more heat transfer surface area. My engine block was cleaned throughout to grey cast iron and it has never seen anything but a 50% antifreeze mix so it remains rust free,

Tom Brady

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Thought I would add to the radiator tag collection. Mine is a 54 xk120 OTS original radiator.

Thanks for that! This fits in the series of Marston Radiator tags I have for the period of (roughly) February to May 1954. Correct?

Bob K.

certificate says manufacture 26 March 1954

Bingo! Thanks for your input. Bob K.

I’m a bit late to this discussion but here is tag on my radiator. It’s in a 1956 XK 140 roadster and was in a crate when I bought the car 30 odd years ago. I’ve been told by an “expert” that the radiator belongs to a 120 but I see from the chat it’s possible this style was fitted to some 140s.

Incidentally, were the tags always fitted in one particular place on the radiator. Mine is on left as you view from the rear.




You’re never too late: this is an ongoing search for the “logic” hidden in the Marston tags.

Your tag P102 16A is from an original XK 140 radiator, but earlier than your 1956 roadster. These tags belong to the second batch of the early xk 140 radiator C.7523 that looks like this one:

Marston probably manufactured 2427 pcs of this radiator version before the final radiator C.9616 was introduced in May 1955.
The first batch (about 750 pcs) had the “standard” Marston tag, but the second batch received the “MEL” type of tag.
I’ve seen this tag on the backside of the XK 140 radiator and it was positioned on the left side. See photo below.

I cannot see which type your radiator is (C.7523 or C.9616) but it might be an original early XK 140 radiator, later fitted to your 1956 XK 140. The later XK 140 radiators didn’t have a Marston tag anymore.

Bob K.

Hi all, I just though I’d add my contribution to this. I was thinking my radiator on my '52 OTS wasn’t original because there was no Marston tag, but I’m sure it’s genuine. On the back of the radiator is a tag by RAD-REPS. I don’t know much about this company but they were incorporated in 1931 and operated from the outskirts of London and from the name I can only assume they performed radiator repairs! The slight mystery is that my car was sold new to Yemen and then was in a Danish museum from the early 70’s until 2012 so it would have to have been an overseas repair.

A couple of weeks ago I picked up another radiator which in hindsight I may not keep but it looks to be an early example from the tag with C267 and Oldfield Lane - perhaps 1950?

The overflow pipe is copper too.


Cannot explain why your radiator has a “British” repair tag . But you shouldn’t exclude that someone needed a replacement radiator for your XK 120 and “found” this one. Is this tag in the position where normally the Marston tag is positioned?

Your other radiator is an original Marston radiator from the second batch they produced. The very first batch of about 100 pieces was installed by Jaguar in the period from October to December 1949. The second batch of about 900 pieces was installed from June to August 1950.
Your serial number 598 was probably used in the production of the XK 120 in July 1950.

Bob K.

Bob K.
If you are still tracking this information, my XK-140 SE (OTS), S811297, (manufactured 4/14/1955) has a Marston Excelsior tag with an order #P102 15A and Serial #303. My car is in mid-restoration and hasn’t run in 40 years. All numbers are matching. Does it sound correct that the Serial Number would be that low? Any thoughts on what re-core of that radiator should cost? I have been quoted $1,000 + by local shops. Any insight would be very much appreciated.
Tom A


The Order number P102 15A is a unique batch of radiators made for the early XK 140 versions. As far as I can see there was a first production run of about 750 pieces with the old Marston tag, looking like this:

For the second production run of about 1700 pieces, Marston used the “MEL” type of tag looking like this:

I had your tag already in my system and it is fully correct for an early XK 140, but looking at the very early serial number I guess it might have been used on an earlier car than your April 1955 version.
As an example: serial number 600 was used on S814028DN of February 1955

Bob K.

Bob K.
I am attaching a photo of the serial tag FYI. Wondering how it might be from an “earlier” car?
…are you thinking it is a replacement or swap from long ago? (the car has been is storage for the last
40 years)

Tom A


Like I said: it’s a very early Radiator number and it must have been in Jaguar stock for months when it was used for you car. This is of course possible, but it also might have come from another XK 120 manufactured still in 1954 (which is more in line with the serial number).

Bob K.


Thanks for your reply. The RAD-REPS tag is on the back of the radiator - the thick black line you see at the top of my picture is the overflow pipe. The front is missing the tag and I am thinking (if it is original which I suspect it is) that the tag may have been removed when RAD-REPS did their thing.

Appreciate the date on the other one - just need to find someone with a July 1950 car minus a radiator now!

I could have started another thread but figured this was as good a place as any for this question.

My radiator pictured above (second pic in the 19th March post) seems to have the original paint finish which appears to be gloss black. Schmidt says they were painted in a gloss lacquer, but the JCNA judging guide specifies that they should be semi-gloss. Does anyone have any thoughts on this one? They were a supplied part so if would be understandable if they didn’t match the jag semi-gloss finish.

IMO all laquer finishes in those days turned out semi gloss, you’d have to flat & polish to get gloss.