Bit of a problem with my M Reg Volvo 440 TDi, Brief history,

About 6 months ago Cam belt broke and wrecked the head, managed to find a new one that I had skimmed and the garage fitted it with no problems.

Then about 2 months ago Radiator sprang a leak I replaced it and apart from a very slow leak from where the Fan thermostat scews in all fine (will fix when weather warmer as I have to work in the street not fun at this time of year)

About 2 weeks ago driving into work the tem gauge went up as normal then did not stop went on up to horizontal (Norma is between 4 and 5 O clock ) then suddenly dropped back to normal. This happened a couple of times over next few days

I thought that it would be the thermostst sticking so took it into the garage fro them to replace it, they checked it and found it OK, but they noticed that there was alot of pressure building up in the coolant and suspected that the head Gasket had gone.

They did a "Chemical" test on the coolant and that came up negative, there is no water in the oil and no oil in the water. I am not convinced that their concerns are correct and that the head gasket is actually ok. Question is what else could be casusing the symtom of the pressureising of the coolant

All sugestion greatly aprechiated

Phil