I've got a bit of spare time tomorrow to look at mechanical gauge which I think has given up, previously I removed and checked the oil the relief valve and it moves freely. I've acquired another gauge to try out, if that comes back as well with a unusually high reading, what else could it be, a blocked oil gallery or oil filter..... Should I try running and oil flush additive and dump the oil again?

When I start the car, the gauge goes straight to 85-90psi and stays up there even when at operating temp.

Another question to remove the glass cover to a smiths 52mm gauge to remove some foreign matter, is it just a small screw driver to carefully lift the chrome ring off?

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SPO41 Mk2 Cooper S very original
1993 R32 Nissan Skyline GTR

Do you have an air compressor to test it with?

Yep I sure do, what's the theory/ process to test ? I'm guessing set my compressor regulator to a certain psi and give it a shot up the gauge?? 60psi on the compressor= 60psi on the mechanical gauge

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SPO41 Mk2 Cooper S very original
1993 R32 Nissan Skyline GTR

Yep thats what i would do. Will give you a rough guide at least. Make up a test hose with hose clamps. Just be careful of oil spitting back at you in the face.

Cheers works well, the replacement gauge holds consistent pressure, holding the same reading as the compressor, managed to remove the chrome bezel pretty easily though the rubber gasket is shot

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SPO41 Mk2 Cooper S very original
1993 R32 Nissan Skyline GTR

Does anyone know where I can get the gasket which sits between the glass and chrome bezel, is it a rubber o ring or a putty??

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SPO41 Mk2 Cooper S very original
1993 R32 Nissan Skyline GTR

3mm sponge cord seal

http://www.ebay.co.uk/itm/NEW-3mm-Spong ... 4628490010

Spewing just re assembled with black auto glass silicone, I thought it was a putty the old stuff was like a crumbling rock! Thanks for your help anyway

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SPO41 Mk2 Cooper S very original
1993 R32 Nissan Skyline GTR

I get about 90psi idle pressure on my 1275 when engine is cold, drops to about 40psi at idle when the oil is reasonably hot (after about 20 miles) but this is using 20W50 grade.

This is using standard 'thimble' pressure relief valve and standard spring, I have tried the ball bearing set-up in the past and ended blowing out one of the gallery plugs when pressure was over 120psi... And that was using 15W50.