Oil light on when warm

[v8viva]

Without wishing to go over old ground,i have a standard 3.5 rover v8 which was stripped last year and had new big ends/mains,new cam and headgaskets and put into my HB viva.Finally got it all fired up and running now and the engine is sweet...pulls like a freight train,but when it gets hot,the oil light starts to flicker.Once its pulled off idle to say 1000rpm,the light goes out and doesnt come back on until the revs drop down to 850 again.The oil pump gears werent changed so is this a good starting point(the oil pressure switch is brand new) and should i change the relief valve at the same time.If so is it worth fitting an uprated spring(one of them claimed to raise oil pressure 10 psi across the range?)
Thanks in advance....Gary

[ChrisJC]

What grade of oil are you using? If it's 10W/40, or similar modern thin oil, then that's probably the problem.

I had 15/40 and my 3.5 did exactly what you say. 20W/50 and it's fine.

Chris.