Freeze plugs - XK-120

What freeze plugs should I use on my Wife’s treasure 120 FHC?? Disk or cup???
Tnx, Eric

Whatever you take out: it’s not an option to swap between types.

IIRC, the 120 had discs.


They are inch size discs, 1-3/4" as I recall, not metric, and are called CORE plugs or expansion plugs, never freeze plugs.
Here is the original manufacturer.
Click on Installation Recommendations for instructions on how to install them.

There is a smaller one down by the starter motor, but that is just an oil passage so you don’t usually have to change that one.

…except, in manys’ vernacular, “freeze plugs” is an accepted referent.

Properly, you are correct, but most everyone understands the term.

Or misunderstand the term; they are no guarantee at all to protect a block from the effects of freezing water. Guess how I know.

Oh, you aint the only one!


On a kinda opposite tack, I bought a Humber Super Snipe, back in November of 1990. It had sat in the same position, outdoors, for at least 10 years prior to that. i stored it outdoors.

Fast forward to April, '92: I dragged the thing inside, and let it warm up. After a day or two, I began checking to see what condition its condition was in… pure water in the cooling system.


Long story short, the engine had no, none, zero, zip, NADA freeze damage, and after some basic maintenance/clean-up, served as my DD for the next year.

It didn’t leak oil.

It started in the coldest of weather.

The heater would blow you out.

I’ll NEVER understand that.

Don’t forget the two 1 inch ones behind the exhaust manifold.

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If you Google, Alan Marshall humber hull UK, you will see the world’s biggest and only collection of Humber cars is up for auction as the collector is retiring.
I had the pleasure of visiting his private Humber Museum a few years ago. Interesting read. Super cars.

I knew there had to be one of ‘those guys!’


Yes, but now he’s retired the collection will be broken up and gone forever.
Sign of the times I’m afraid Paul.

I guess you got lucky, Paul, with your Humber. My old dad was not so lucky with his Plymouth.
I don’t recall ever seeing a Humber in Chicagoland.

For Eric, I confirmed the block plugs are 1-3/4" discs, and 1" discs in the head exhaust side.
red XK140 block 002

That got me thinking, I wonder why they used brass screw plugs in the head valley, when Hubbard plugs would have been cheaper. Those brass plugs can be hard to remove. I used a propane torch on them.

BTW they are called core plugs because they plug the hole left by the baked resin sand core that formed the shape of the water passages during the iron pouring process in the sand mold.

I will never understand how i got THAT lucky.

I am quite aware of their operation: that does NOT mean that, in many folks’ vernacular, “freeze plugs” is not a valid identifier of the parts, themselves.

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And here I always thought they were called Welch Plugs. :innocent:

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Yes, the Welch brothers were the original inventors, and the story is that in 1905 they were out road testing a car they had built, and a pipe plug fell out, so they hammered in a coin to get home, and an idea was born.
At some point they sold their idea to Hubbard Spring who still make them.

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Over here the welch washers are the early type - simply dished.Core plugs are the “U” shaped ones ( if you get my drift?)