Coolant pressuriseing on over drive

The message from "James Salisbury" contains these words:

It's probably an effect of trying to decellerate all the water in the pipes. When you're revving it's all going round quite quickly - when you suddenly drop the revs all that water has to slow down quite fast. It'll quite probably suck a bubble down from the breather pipe into the main circuit - from which it'll pop back up again.

Try clamping the breather hose and see if it does it then.

Any suggestions why if the the cap is left on, the pressure builds up whilst driveing, so even if the engine is left to cool for 7 hrs there is very substantial pressure left in the system.

The message from "James Salisbury" contains these words:

Oh, that's a blown head gasket, almost certainly.

It has been in a so call garrage, he claims he has replaced the gasket five times, used new head bolts every time and has also put in a second hand block and head and had the head pressure tested. He also uses hoylamar blue on the gasket faces.

Pleas take a look at

All comments welcome,

Crack/hole/metalworm somewhere in the block?

The message from "James Salisbury" contains these words:

That'll be why then. Head gaskets are not supposed to be used with anything except clean bare metal.

The message from "James Salisbury" contains these words:

Dunno.

And all the above can mean sod all unless he has had the head AND block checked to make sure they're actually flat. If everything is OK, there's no need to use hylomar.

Warped head, warped block.

AKAIK Vauxhalls over the last ten years at least have Torx-headed bolts. I think your mechanic has been pulling a fast one.

Let's face it, to replace a head gasket five times, using new parts every time, is going to cost a lot of money (there are other gaskets involved in the job too). So either he's telling lies, or he dosn't know what he's doing, or the engine is damaged in another way. Has the head been skimmed? It should be. Water leakage between the waterways and the rear cylinder is quite common.

Time to find an different garage, one that knows what they're doing.

I would do the Combustion Leak Test again, maybe this time with a fresh batch of chemical, as it is not unknown that sometimes it gives false negatives. To settle the question once and for all, it is also worth trying an alternative: testing for any gaseous hydrocarbon with an Exhaust Gas Analyzer (MOT stations have it; I've got one left from the good old days) in the open coolant filler while the engine is set at part throttle.