[Lee]

I think from reading some of the comments on here, it's best to consult a trained professional, oil is not a coolant, its a lubricant, yes some cars have oil coolers but that is to stop the oil breaking down.

Southwell,

The K series engines are renowned for heads going, but to be honest, yours doesn't sound like a head or a gasket has gone, if it is not using water and the expansion tank is not pressurising you might be ok, you would see lots of smoke if your losing water, also, have a look at the oil, has it gone milky, if it has then this is a good indication that water is in the oil and you either have a crack in the head or a blown gasket.

Are they K series engines on hydraulic tappets? if you have low oil then it will sound tappety, top it up and run it for a minute and see if it quietens down.