What is this called and why is it leaking?

[ian_touring]

I've taken on a project midget 1500 that's had some work done (clutch, brakes, renewed front + rear suspension. A friend's dad has emigrated and sold up his project, so we're looking at what needs doing to get it through an MOT and have some open-top fun and frolics!
Anyway, when it gets up to temperature, the temp gauge reads halfway between hot and cold, and stays there, the radiator hoses get suitably hot, but it doesn't feel like the coolant system has much pressure in it, and there is a small but significant coolant leak from this round black plug-type thing:

Does anyone know what this plug is called, why it is leaking (if that's not a silly question) and what I can do to stop it leaking?
Thanks in advance
Ian

[steviejasp]

It's a core plug.
May be rusted if steel or if brass, just get a new one and replace it.

[Hammer67]

That`s a core plug. Made of steel and is pressed in a hole in the water jacket, designed to save the block if the water freezes inside. Will have rusted from age and lack of antifreeze. Proper repair means pulling it out, cleaning up the hole and pressing new one in. Bodge repair could involve radweld, silicon sealant or chewing gum.

HTH

[ian_touring]

steviejasp said:

It's a core plug.
May be rusted if steel or if brass, just get a new one and replace it.

Great, thanks, time to go shopping for core plugs.
Ones that don't rust...

[ian_touring]

Hammer67 said:

That`s a core plug. Made of steel and is pressed in a hole in the water jacket, designed to save the block if the water freezes inside. Will have rusted from age and lack of antifreeze. Proper repair means pulling it out, cleaning up the hole and pressing new one in. Bodge repair could involve radweld, silicon sealant or chewing gum.

HTH

So it sacrifices itself in the name of the block, I wondered if the block may be split because of what feels like low pressure in the coolant hoses. I did find a random small blob of silicon sealant when I flushed the coolant...

"Pressing in a new one" sounds like it needs more than just a hammer and a well-judged socket to push a new one in. Best left to a professional spannerist with some kind of press?

[Hammer67]

No, not difficult to fit a new one. Clean up the hole carefully, don`t enlarge it with stuff like wet`n`dry paper, run a film of sealant round the edge of the new plug and tap it in square with an old socket.

Don`t be surprised if when you get the old one out you find the block water jacket silted up with crud, try flushing it out but if it`s bad the only real answer is head off I`m afraid.

[ian_touring]

Okay that's given me some confidence to have a go this weekend. Here's hoping the head doesn't need pulling off.
Thank you to the PH massive as always.
Have yourself a
Ian

[na]

When you flushed the coolant did you flush, back flush, clean, flush, back flush and finally flush the rad, heater matrix and engine block, removing the engine block drain plug - if not take this oppotunity to do so

if the coolant hoses are old but in good condition keep them if they're new expect to possibly need to change them when they're 12-18 months

If you've not got one then the best £7/8 you can invest in the car is to buy an owners Handbook - (Ref: 0058) http://www.mgocshop.co.uk/catalog/Online_Catalogue...

If you want I can post my usual advice for new owners

[wildoliver]

I'm sure you've got shares in those owners handbooks

[na]

wildoliver said:

I'm sure you've got shares in those owners handbooks

I wish I had

They've got so much info in them I think every potential owner and new owner should have a copy and thorough read it and follow the servicing schedule that way they'll know about their car and cut down and prevent a lot of potential future problems

Plus they can tell some long standing owners stuff they should have learnt long before - if only they'd bought the Handbook