Bongo Fury

Hi all, not having much luck with my Bongo at the moment, hope I can get a bit of advice, the other day she started to over heat, managed to get home, checked the expansion tank that was empty, let it cool down then topped it up, started her up and seemed to run fine and no overheating, went for a run and all ok, this morning there was no coolant in expansion tank so topped up again and ran it and spent ages looking for leaks and can't find anything, looked at the expansion tank and that was now full to the overflow pipe, also what sounded like a belt a slipping was now very loud as the seats were up so I wondered if all this could be down to the water pump, oh and it's a 2.5 diesel. Thanks.
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If the coolant drops below the header tank you need to find, and fix, the leak, then the system must be bled.

If Bongy overheats there is a high chance of cracking the head.