essential service item?

Recently our van has been using water so everyday I top it up before I go to work and then again before I drive home and at the weekend before last coming home from surrey it very nearly over heated and we had to stop and release the pressure and top the water up before we could carry on so that evening I removed the thermostat and went to work the following day for it to do the same on the way in on a coolish morning and then twice on the way home after I stopped and got some k-seal and put it in so as a desperate meaure the rocker box came off so I could torque the head bolts down a little tighter to find they were loose I got a full turn on one of them just to get it to the setting it should be at and I have done the head gasket twice and know without a dought that they were all done up as they should be so at service or any sign of over heating I will check them first So far since I have not topped the water up and I'll be fitting the stat back tonight and it has been running very well.

Perhaps the bolts need replacing...

I always put some threadlock on the threads before putting head bolts in....

there is no point putting thread lock on any item that gets hot we use green loctite (shaft grade) to lock the threads on our shocks at work and if they need servicing we just warm the alloy end fitting a little with a heat gun and they unscrew no probs I have a extra weight glued onto my pointer base with the stuff and its only two flat bits of steel.