It happens to be a Bedford Rascal van, but I guess it could be any engine.

Water disappears rapidly out of the radiator and ends up in the sump as custard. I'm going to change the head gasket tomorrow but can anyone think of any other reason for this happening?

cracked cylinder head?

likely to be head gasket though

All will become apparent when you remove the head, the cylinder with the leak will be the cleanest (steam cleaned!)

Thats a Suzuki apart from the badge innit? Quite a simple iron block engine arnt they? If you cant see any obvious fault consider a porous cylinder wall, really a sump off job so you can look up the bores below the pistons.

pretty prone to head gaskets and the heads warp,not an easy job to do as the floor gets in the way,ive scrapped plenty cos of engine probs