Hi, I've just done the clutch, went to fill up with water and it all just poured out the back,

there's a massive hole and I found a metal plug just underneath it, just wondering what it is how it would just fall out and if it just pops back in.

Any help much apreciated.

Mike.

Do you mean it's pouring out of the back of the clutch bell housing (which would be weird), or the back of the radiator expansion tank?

It will be a core plug. You need to get a new one and fit it with some sealant.

Dave.

Core plug? just at the rear of the engine block yea?

Why would this of came out, what's it there for

and is gasket sealent ok?

There will be several of them in various places around the engine block.

They are there to fill the holes left by the sand core used in the casting process of the block. Hence the name Core Plug.

They generaly come out because of corrosion meaning that at some stage in it's history, the car has had insufficient antifreeze. They may also come out if the coolant in the engine freezes, however, contrary to popular opinion, that's not why they are there.

I've always used Hylomar as to seal them, but anything similar will do. I don't think silicon sealant will work. Main problem fitting them is access, they need to be hammered in straight.

Dave.

They have to be tapped in bit by bit and kept square. Otherwise they will leak. Ideally use an anaerobic sealant which is only available at engineering factors.

As Davren says they are there to fill holes that remain as part of the casting process. They usually pop out because the engine has not had any antifreeze/coolant or they have corroded for the same reason.

If its right under the inlet manifold you will have to strip off all that to gain access. Core plugs are made of thin steel with a turned up edge and come in various sizes. They MUST be fitted square or they will fall out again.