I have recently had a problem with my 1995 Bongo. I hadn't driven it for around a day while we had all of the snow and freezing conditions. I took it out for a short drive but got stuck in traffic. I saw the temperature guage shoot up and then the sound of boiling water coming from the engine bay. To my horror when I pulled over and checked under the hood I found that almost all of my coolant had been pushed out of the overflow pipe

I crawled into a local car park and refilled the coolant levels. I left it to cool down for an hour or so and then managed to get it home. It started to creep up again but I made it.
I have now taken it out for another short drive a few days later and the same thing has happened again. Temperature has shot up within about 3 miles and the antifreeze is starting to boil. I managed to get into work after pulling over three times to let it cool down. The strange difference is that now the pipes coming from the bottom of the antifreeze tank are cold.
Please help me, it is my only form of transport and I have no idea what to do. I thought that maybe the thermostat might be stuck in a closed position or something, based on stuff I have read on the FAQ. But I am unsure. Any ideas on how to diagnose the fault would be great!
Thanks
Jason