Td5 head gasket/cracked head? Inflated rad!

[Cret]

I've thought that the head gasket must have a slight leak for ages on my disco as it seemed to be using coolant and I wasn't finding leaks at all (after replacing one damaged pipe at least), but since it seemed minor and I use the disco infrequently (it's not my daily driver now but my 'utility' truck) I hadn't worried too much about this, just made sure it didn't get hot, and topped up the coolant as required.

Recently it's had a couple of runs where it's been able to properly get up to temperature and do a few dozen miles, and I noticed something horrible some time later. The radiator has inflated!

Now I replaced the expansion tank cap some time ago because I wondered if it was faulty, and it looks like ironically the new one has broken. The yellow plastic bit in the middle seems to be crooked, so I'm guessing it's jammed somehow.

So I'm guessing that pressure in the coolant system has been able to build up more & more until it's turned the rad into a balloon! Very nasty.

I'm assuming at this stage that there's no way in the world that the head gasket could still be in one piece with this sort of thing happening.

What I'm concerned about is the possibility of a cracked head? How common is that, and is it just overheating that causes that?

I've been careful to keep an eye on the temp gauge and it's always been kept at normal levels. It's crept above a couple of times but only just, then I've given it a rest before topping up coolant.

Is there any way to know if the head is ok before removing/dissassembling to do the head gasket? I know about the dowels and stuff when doing the gasket, but where can I buy the metal ones?

Many thanks!

Jim