How To Replace Welch Plugs

In this article we are going to take a look at what is involved in replacing welch plugs, otherwise known as freeze plugs, expansion plugs or welsh plugs with an ‘s’.

What we are doing with this article is covering only the actual removal and replacement of a welch plug itself on a scrap engine, there are too many variations to be able to accurately cover what has to be removed before gaining access to the plugs so I will have to leave that up to you (for example – on 6 cylinder Falcon engines the exhaust manifold needs to be removed to gain access to the main welch plugs). For the time-being anyway, I hope to have detailed welch plug replacement articles done for the more popular engines some time in the not-too-distant future.


Ok, on with the show. The first thing you will need is replacement welch plugs of the right size (if possible check the sizing of the new against the old before fitting), a punch or drift, a hammer, some sealant (more on that in a moment), some emery tape or sandpaper, a small mirror if you have one, a set of pliers or vice grips and a socket or tube that fits snugly inside the new plug.

how to replace welch plugs

To remove the old plugs it is simply a matter of picking one side and knocking it in with the punch and hammer. The ideal situation is where it ‘turns’ so that the opposite side comes out – this doesn’t always happen though and don’t stress if the plug goes into the block instead of one side coming out.

how to replace welch plugs

After a bit of punch and hammer work you should be able to grab one side with the pliers or vice grips (multi-grips work too). With a bit of effort you should be able to pull the offending welch plug out from it’s hole.

freeze plug replacement

Next up we need to ensure that the new plug will have a clean surface to seal against. Here we use the emery tape or sandpaper and run around the edge of the block to clean up any rubbish. Having a small mirror to check your work at this stage is handy.

welch plug replacement

welsh plug replacement

Once you are satisfied that everything is good it’s time to check the new plug’s size and if that looks good it’s time to run some sealant around the outside edge of the new plug. My personal preference here is Stag Jointing Paste (available at Repco, Super Cheap etc), but I know of a few people that prefer to use a non-hardening sealant such as Aviation Form-A-Gasket (also available at Repco, Super Cheap etc). I can tell you that I have never had a replacement welch plug leak using the Stag but I’m sure either one will do.

welch plug replacement

Once the sealant is in place, take the socket or tube and fit the new plug up to the block. The idea here is to evenly knock the plug in until it sits just inside the ‘lip’ of the hole in the block (a mm or two below the block surface).

 

You should get a good idea of where it is supposed to sit from looking at where the old plug sat before you removed it. Running your finger around the edge will give you a good idea if the new plug is seated evenly or not.

how to replace freeze plugs

freeze plugs

freeze plugs

Now you can wipe off any excess sealant and go on to the next one.

13 thoughts on “How To Replace Welch Plugs

  1. Ive heard that you need several different size plugs for the engine as the plug hole size can vary due to the casting process for the block
    do you need to try and judge which size plug is correct and what happens if the replacement plug is too big, does it bulge in or out when installed

  2. Hi Arthur,
    As far as I am aware there is only a ‘standard’ set of sizes for welsh plugs. Over the years I certainly haven’t come across any problems using the welsh plug sizes that were listed for the particular engine at the spare parts suppliers. Obviously there are metric and imperial sizes to suit the age of the engine but I think that is as far as it goes.

    Regards,
    Craig

  3. Hi, can anyone please let me know how many hours of work has to be done before the Welsh Plug can be replaced.. My mechanic charged me about 5 hours of labour for my 15 year old Toyota Camry.

  4. Edward, it sounds like you’ve been ripped of in a big way!!..I’d go to the relevant authorities.These people need to be stopped!

  5. Thanks for that helpful article. The plugs have a tendency to fall apart if they are badly corroded, which is usually the reason for changing them, which can make getting them out that much more difficult. I’m just doing them on my TR Magna 2.6 EFI, a really fiddly job involving removing radiator and heater hoses, lots of little pipes and a few electrical connections, the fuel injectors and fuel hose, the throttle body, inlet manifold and AC compressor, all of which sounds OK and the service manual makes seem simple, but so far has taken about 4 hours and lots of skinned knuckles just to get the old ones out, so 5 hours for the whole job could be reasonable.
    And yes sort of, the radiator has to be drained, or will drain itself, when the plugs are removed

  6. With regards to the 5hrs labour charged on the Camry, it may depend on the engine. If it is a 4 cylinder then forget it… I have just done two welch plugs on the inlet side of mine in under an hour. A V6 model though… It is a more cramped fit and a lot more work may be needed to gain access to the welch plugs (ie: removal of exhaust manifolds, power steering pump, air con pump, altinator, drivers side drive shaft etc….) Then all those parts need to go back on once the plugs have been fitted.

  7. Dear Richard,
    I am replacing the welsh plug in my MG TC 1949 model. I have recieved the plug which is 48mil and it is same size as the one that come out ( dish shape). Can you tell me if the dish plug expands when you tap it in for this one fits neatly but is loose?

    Regards Max

  8. Hello Max,
    I’m sure that they should be a tight fit when cold, as even though they do expand a little when hot, they still have to hold back the pressure in the cooling system. I replaced the plugs on my A+ motor (in my Moke) a number of years ago and recall that they are the dished style rather than the type shown above, and that they were a snug fit, certainly not loose. Also use only a little jointing paste, as the excess could potentially block some of the fine galley-ways in the block (or reduce flow).

    It may be that the block has corroded a little where the plug fits in, hence the plug being a little loose?

    Sorry I can’t be of more help.

    Cheers,
    Richard

  9. the dish type are put in the hole and you belt them with a punch in the centre to expand the plug to make them a tight fit

  10. I have found your site interesting….. I have a very old 1983 Mazda 323 (was a 1300). We put in a reconditioned 1500 engine quite a few years ago …. I need the Welsh plug replaced & don’t want to get ripped off for labour…. What would the approximate number of hours?

  11. Norma, that depends on which welsh plug! For example on my Mazda diesel light truck, the ones on the rear cylinders passenger side would only take half an hour to gain access, still tricky to get to, but doable. The ones on the front cylinders, however are behind the fuel pump. A recent removal and replacement of said fuel pump took me three days!
    One possible fix was done by a 70y.o. hitchhiker on the Stuart Hwy mid 70’s. I cooked dinner while he patched a steam hissing plug on the back of the head of an HT with Araldite. Was still there 5 yrs later when I drove it into Simsmetal.
    A removal technique not mentioned yet is getting a bolt screwed into the plug, or a pipe thread tap. And using a nut to pull that assembly out just like a steering wheel puller. Being able to use a punch and hammer is a fantasy in many cases.

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