I am experiencing oil pressure anomalies on a totally reconditioned engine. On starting the engine the oil pressure climbs to around 70 psi then promptly drifts back down to zero after a few seconds (oil still cold). I have replaced the sender and then the gauge from a scrapped 1977 Mk2, both made no difference.
Next I replaced the whole filter head, as it occurred to me that the ‘blocked filter bypass’ was possibly coming into play - correct quality new filter and correct grade of oil is used - still the rise and immediate fall in pressure reading persists, regardless of the engine rpm. Throughout all the starting and stopping the engine sounds quiet and smooth, so it would seem that it is getting some oil.
Did you install a new oil pump? One of the new upgraded ones? The pump suction tubing fittings are a little tricky. Might want to check all the correct o rings are in place. Seems you have confirmed you have very little oil flow. Might as we’ll check for rod and main bearing clearances while you are at it.
It may be a electrical problem , ie wiring or the like , I would fit a mechanical oil pressure gauge , by tapping in to a main oil way on the side of the engine block !
The mains and conrod bearings are new on a reground and polished crankshaft so should be good oil pressure wise. The oil feed and pick up pipes were ‘smoothed’ to ensure a better and easier fit through new O rings. I am going to investigate the oil pump today, having lost 3 hours sleep in the middle of last night thinking about it.
I will check your suggestion. I am currently changing the oil pump to an original H. E. pump which is in good condition ( although I have found nothing wrong with the pattern type pump). I have checked the feed to the main bearings all clear and obviously getting plenty of oil. So I am fairly happy with the mechanical side of things, your suggestion sounds like a good idea - will let you know.
I called a friend who is more knowledgeable than I am with things electrical, showed him your email. He set to and carried out some tests with meters and things and found that you are absolutely correct about the fluctuating current from the regulator. Once the engine has run for a moment the voltage drops drastically on the oil pressure gauge feed wire.
Many thanks for your insight, much appreciated. 3JagsPete
Sounds like you need a new instrument voltage stabilizer. I found these on a Moss website for an MGB, Solid state ones in positive or negative ground. Not too expensive but I have no idea how well they work. Any forum members with experience? Here is the link. https://mossmotors.com/mgb/dashboard/solid-state-voltage-stabilizers