"Are you a scope user?"

You make it sound like an addictionTruth is, I dabble when time permits or there is a need.

Follow your thinking on this, probably is a pump issue. Actually sick of looking at this van. It has had so many major issues, would be nice to just get it out the door. Today switched pump for vehicles original, does seem a little smoother at idle. Temperature problem remains.
By fitting a 100ohm resistor in place of temp sender(115c on scanner) engine will start cold.

Will have a go at scoping pressure decay cold & hot tomorrow if people will leave me alone long enough.

The guy who carried on driving this until turbo fell to bits is back from holiday on Monday. Will try interrogation techniques to find out if this was a prexisting fault. It's actually quite trivial compared to the state van was in when it arrived under its own power with following smoke screen.