What oil pressure should my M20 have?

[E30Idea]

I have just finished my 2.7 stroker project and I have my first issue. I am getting a low oil pressure light at idle. When I rev it goes away. First I bought a new pressure sending unit for the block, no fix. I hooked up my MAC tools oil pressure guage to it today and when warm it reads apx. 5psi at idle and 30psi @ 4-5k rpm's.

I think this is very low (I could be wrong). Honestly, it sounds like its time for an oil pump, but some concrete numbers would be nice to have before diving into the bottom end. So, I have the following quesions:

1- What should and M20 have for oil pressure when warm?

2- Is the Royal Purple 15w40 the wrong weight oil?

3- How much effect do the crank and rod bearing's have for supplying oil to the top end in these motors? (bottom end has 116k miles on it)

Thank in advance for the help guy's. I did search and unless I missed it I did not find what I am looking for.

-Ryan

[PeaveyBassist]

My m20b25 w/ oil cooler with unknown mileage (probably over 200k) on the oil pump with castrol 20w50 dino oil when cold has about 55psi at idle and obviously goes down once the oil warms up. The oil temp almost NEVER gets above 200 degrees. When it is about 180-200 degrees, oil pressure at idle is around 8-10psi. The light is supposed to come on at 7 psi, but I never see it so it has to be above that. At 2k, it is around 25-30 psi. You probably want to try a new pump. Question 3 I cannot help you on. Btw, my pressure sending unit is put where the stock pressure switch is on the side of the block below the filter housing and the temp sensor replaces the drain plug. All VDO stuff.

[Adrian_Visser]

bentley specifies 7-28psi at idle and 57-85psi at WOT and yes worn main bearings and rod bearings will greatly affect the oil pressure of the engine as the pump has to pump more oil to fill the larger spaces between bearing journals. 115k isn't that much mileage though

[PeaveyBassist]

Weird... My oil pressure never really gets above 60psi once the oil warms up. Even at 6k rpm.

[E30Idea]

Thanks for the info guys and by all means, anyone can feel free to add more info as they see fit.

I have to ask, should I take the time to feeler guage the main bearings and rod bearings or should I just toss a new pump in it? The engine runs great, lots of power, and sounds tight (inside) but it did sit for 3 years before being put back into use.