I've got some problems with my van again

It's been off the road for a few months now after it got the dreaded clutch rattle and a few other problems and I thought it's time to get it back on the road again. I changed the clutch, brake pads, a few various bearings, speedo sensor, brake/clutch fluid and I drained the cooling system, flushed it through and put fresh coolant back in. Took it for MOT and it flew through with an advisory on tyres lol.

A couple of days running round and not a problem until last night. It was getting a bit cold so I decided to put the heaters on, they came on hot and after a couple of minutes they started to blow cold air, the temperature gauge was bang on half way as normal and never moved, when I got home I lifted the bonnet and noticed the expansion tank was full to the top and there seemed to be a lot of pressure in the pipes. I noticed that all the pipes where hot apart from the pipes running to the expansion tank, I took the cap off the tank and it started to bubble out the tank with the pressure, the water in the tank was stone cold until the hot water bubbled up the pipes and into the tank and it settled.

I left it for a few minutes and when I went back the tank was empty, I topped the tank up and squished all the pipes, started the engine and squished the pipes some more, checked the heaters and they where blowing hot, temperature gauge in centre and all pipes where hot.

I took it out for a 20 min drive and temp gauge stayed in middle and heaters kept blowing hot but when I pulled up at home the heaters started blowing cold again. I lifted the bonnet and the expansion tank was full again, loads of pressure in system and the water in the bottle was stone cold but all pipes round engine hot.

Its not the EGR cooler cause I bypassed that months ago and its not over heating so dont think its head gasket (or I hope not)

Anyone got any ideas? could it just be a bad airlock, thermostat or water pump??

Edited by smittymosschopps on 23/09/2013 at 20:54