Classic cars forum & vehicle restoration.

Rootes75

We have made the most of our 1947 Minx this year, taking her out most weekends when possible.

Well, last weekend we took her out and when we got back she was pouring coolant out her overflow pipe, properly pouring out. Half a pint came out into the jug.

My thoughts are that it's all down to the radiator cap...my issue is that I can't find a replacement...
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Various Rootes Vehicles.

alastairq · Joined: 14 Oct 2016 Posts: 2278 Location: East Yorkshire

Rusty · Posted: Sun Oct 11, 2026 1:56 am Post subject:

E'Bay "may" be your friend!

One of our car club members has a 1950s Singer 1500, and it needed an unusual radiator cap made of "unobtanium", and he managed to get one off E'Bay. It wasn't cheap, but it's working!

alastairq · Joined: 14 Oct 2016 Posts: 2278 Location: East Yorkshire

Meant to add, is the cap a 'screw fit' or a 'push & turn [more modern ] type?
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Dellow Mk2, 1951 built, reg 1952.
Fiat 126 BIS
Cannon special [1996 registered. Built in 1950's]
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Ford Pop chassis, Ashley 1172 bodyshell, in pieces.

Rootes75 · Posted: Sun Oct 11, 2026 10:34 am Post subject:

It's a push and turn type. I have had a good look and it has nothing stamped on it to indicate it's rating.

I'm sure I have a parts book tucked away somewhere so I'll try and dig that out.
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Various Rootes Vehicles.

Rusty · Posted: Sun Oct 11, 2026 10:59 am Post subject:

The one on the Singer is 7 PSI which was a common standard back then. A lot of farm tractors and equipment used the same size and style of cap but set at "4" PSI. This is a "round" cap with no "ears" to turn it by and a bit larger than the more modern type from the late 50s on! It is also the "push and turn" type, and roughly 3" across! (I don't have it here, but "approximately" 3" across or just a bit smaller)

alastairq · Joined: 14 Oct 2016 Posts: 2278 Location: East Yorkshire

Does the original cap have a spring in it?

Or is it simply the cap, with a {solid?] rubber gasket inside?

I do wonder why it suddenly 'pressurised' to the extent the coolant poured out?

Was there a 'temp gauge' warning?

It might be an idea to step away from 'originality' for a moment, and feed the overflow hose/pipe/ down to an overflow catch bottle? If the [new] cap is two way [allows some pressure to build, but also has a 'suction' valve inside, to allow air back in when the engine cools down, perhaps? Saves the coolant being 'total loss?'

My Dellow has a really large diameter cap [compared to the likes of Morris Minors, Sprites, etc]...Luckily, before I ceased working, I had a good rummage through the stuff used in the classroom side of things....and discovered the cap that went onto a Bedford TM was the same size, and a couple of psi different. Also painted green...I also got the Bedford header tank...just in case something like that might have been useful, at some point????

I have all sorts of random caps in the 'normal' vehicle size. Various pressures too.
_________________
Dellow Mk2, 1951 built, reg 1952.
Fiat 126 BIS
Cannon special [1996 registered. Built in 1950's]
----------------------------------------------
Ford Pop chassis, Ashley 1172 bodyshell, in pieces.

ukdave2002 · Joined: 23 Nov 2007 Posts: 4437 Location: South Cheshire

KIP's cataloge list them as available https://anyflip.com/cnim/ewaq a bit pricey at $19.25 + shipping from the US.

One resolution if you unable to find a replacement would be to fit a replacement radiator neck from something where the right size pressure caps are available.

The necks are only soldered in so quite easily changed.

Or purchase a new neck: https://www.carbuilder.com/collections/filler-neck