Thread: 3.9 v8 oil pressure

Originally Posted by milld

I pulled apart the oil pump and inspected the gears before I Put the motor in- looked perfect.

Just a reminder the gasket for the oil pump is super critical in its thickness, I imagine you had a proper gasket out of a set for it?

I did put a new gasket on it ( ordered it specifically ), but I also remember adding a Small bead of silicon. I tighten down to recommended torque. I hope this hasn't made the gap to big?

I just did another start, light came off just on 3 seconds, after over 4 hours of sitting. The replacement switch has helped but still not the best.

Originally Posted by milld

I did put a new gasket on it, but I also remember adding a Small bead of silicon. I tighten down to recommended torque. I hope this hasn't made the gap to big?

I just did another start, light came off just on 3 seconds, after over 4 hours of sitting. The replacement switch has helped but still not the best.

I've never dared to use anything other than a clean new gasket, after stuffing a pump properly in my youth.(It seized .) A simple enough thing to replace one day. I believe there are instructions about for checking gear protrusion from the pump housing with a feeler gauge, then subtracting this from the gasket thickness to get a good pump clearance.



For the P76 pump pictured protrusion should be betweeen 0.002" and 0.006", with the higher figure being better.

Originally Posted by bee utey

I've never dared to use anything other than a clean new gasket, after stuffing a pump properly in my youth.(It seized .) A simple enough thing to replace one day. I believe there are instructions about for checking gear protrusion from the pump housing with a feeler gauge, then subtracting this from the gasket thickness to get a good pump clearance.



For the P76 pump pictured protrusion should be betweeen 0.002" and 0.006", with the higher figure being better.

mmmmmm that's some pretty fine tolerances. That would mean I could be having consistant low oil pressure? I have never seen the light flicker on though even at real slow hot idle. I will source a gauge and a new oil filter and report my findings.
what oil pressure should I be getting @ cold idle & hot idle?

thanks again for the help, appreciated!

Originally Posted by milld

mmmmmm that's some pretty fine tolerances. That would mean I could be having consistant low oil pressure? I have never seen the light flicker on though even at real slow hot idle. I will source a gauge and a new oil filter and report my findings.
what oil pressure should I be getting @ cold idle & hot idle?

thanks again for the help, appreciated!

Hot idle oil pressure can be as low as 20psi and not risk your engine.

BTW I gauge the deteriation of my Penrite oil by how many seconds it takes for the oil light to go out. 1 second with new oil, 2-3 seconds and I drain it, regardless of age. I think it's about oil stabilisers, part of the oil formulation. I remember when I first met my wife, the el cheapo oil in her HJ Holden took 5-6 seconds to reach pressure in the mornings, Penrite reduced it to 2. Normal running pressure was fine.

It annoys me that my 1990 Vogue hasn't got an oil gauge. Seems to be pretty common these days not to have a gauge. Not even my Dad's MG RV8 (3.9L) has got one and thats supposed to be a sports car.

Originally Posted by CSK

It annoys me that my 1990 Vogue hasn't got an oil gauge. Seems to be pretty common these days not to have a gauge. Not even my Dad's MG RV8 (3.9L) has got one and thats supposed to be a sports car.

Gauges freak out dummies. Many years ago I put a 0-100 psi gauge in my P76. Running, the oil pressure used to sit below half. Passengers would comment on the low oil pressure. Then I fitted a 0-60 psi gauge which would sit over half. Passengers would comment on the good oil pressure.

Warning lights aren't called idiot lights for nothing.

Originally Posted by bee utey

Gauges freak out dummies. Many years ago I put a 0-100 psi gauge in my P76. Running, the oil pressure used to sit below half. Passengers would comment on the low oil pressure. Then I fitted a 0-60 psi gauge which would sit over half. Passengers would comment on the good oil pressure.

Warning lights aren't called idiot lights for nothing.

Thanks for the heads up, I'll try and get one that goes to 60 max to shut the dummies up lol.

Another quick update; I just started her up again after leaving it sit this time yesterday afternoon and it took exactly 5 sec to go out. The replacement switch has made a 3-5 second improvement. Now to source one of those illusive Mahle OC261 filters and hope it fixes the drain back.

Cheers