Since being adviced here to use castrol GPX 10-40w in my over the hill XE i have noticed that when the engine is hot and i is at idle the pressure drops from full to half, it comes straight back up when it's revved.
Is my engine about to say goodnight? or is it just because of the thinner oil?
Go for Vauxhall's own 15/40 oil, meant to be quite good and it's cheap!
When you change the oil, give the oil pressure relief valve a clean out. It might have got a bit gummed up with gummyness. It's located on the oil pump with a big mofo bolt. It's pointing towards the front of the engine and down slightly. It's got a spring in it so be warned!!