oil pressure light help please.

As some of you may be aware my latest project has had gearbox rebuilt and I'm mobile and sorting out various issues with engine.

expansion tank dripping slightly when hot and no HGF signs -sorted with new cap
mechanical advance weights seized-sorted by stripping distributor
Bogging down when hot on gas or petrol-sorted new leads/rotor and cap as original cheap crap.

now drives nicely locally-without issues.

Motorway drive back to mine the oil light appears on tick over when I got home and it was hot-so do you agree my list to check

1) try new oil pressure switch, as I can't find anyone local to borrow a test gauge.
2)pressure relief valve sticking and or partially blocked pickup
3)worn rocker shaft-can't see excessive oil loss
4)worn big ends/mains

does not rattle or knock

what spec oil are you using you can remove the relife valve and check it is not sticking is the cam shaft ok and not worn?

Oil is whatever the previous owner put in it-clean and yellow.

Whoever did the last sump gasket wound it down so tight that they split it out-so I have a new sump gasket to fit and will have correct oil and filter.

I've had the rocker cover off one bank as it was leaking,to be fair I just looked at the rockers and they didn't look black death or feel bad.
Though I'm quite prepared to strip it and look.

Camshaft doesn't sound bad and it goes as well as other 3.5 v8 's I've driven.

You could be right on the grade of oil, weren't these originally 20w50 and now 15w40. as the 3.9 and bigger were 10w40

reckon I have the answer I think I have a pin hole from head gasket to oil way, and when hot the relief spring on oil pump pressure relief valve sticking.

only happens after motorway run, still 19 years old, I reckon it's suffering head tipping issue others talk about

bugger,**** and bollocks
compression test had very very marginal drop on cylinder 7, decided to run with my theory- it has blown across into valley gasket.
Really not that bothered-until I found that the gasket has eaten into block, looking like engine out and strip to deck block=what a Complete ****

ouch that's a bitch
i always expect the worst now when anything goes wrong, it's a bonus then when it goes easy

Think what ****ed me off more is rebuilding the gearbox, toyed with tdi conversion but the v8 with lpg-love them so decide to stick with it.
Now it is a choice of engine out and rebuild or buy another with condition unknown.

Either way a bitter pill. had I not used the motorway-wouldn't have known