Friends, I need some insight what to look for here. Engine oil in the car is Valvoline 20w-50. The oil pressure when the car starts is decent but then as the car warms up the oil pressure goes down. I know it is a bit open question but what should i look for? is there a good starting point? is there a way to test the oil pump? or oil pressure at a specific spot etc.?

Appreciate some help ...

its pretty normal for it to look very low on the gauge at idle and warmed up. I wouldn't worry about it as long as it ahows higher when driving. 

The oil pressure gauge in my ZX sometimes reads near zero while cruising, then pops back into the normal range. It's a brand new rebuilt engine with a brand new Hitachi oil pump. It is not, however, a new oil pressure sender on the side of the block.  it just goes all wonky sometimes. It does make me nervous seeing it like that, but I'm confident that it's getting constant oil pressure.

4 hours ago, MH77280Z said:

is there a way to test the oil pump? or oil pressure at a specific spot

It's very likely the pressure sender that's become leaky inside after 30-50 years.. get a new one.   (On a 280zx sender there comes oil out of the elec.connector!)

38 minutes ago, Reptoid Overlords said:

oil pressure gauge in my ZX sometimes reads near zero while cruising,

Yeah i got that when i put the idle speed near the 500 rpm's.. it's normal (i do have a new pres.sender on my block)

What you both can do very easely is: start the car warm up and let it idle at 700 rpm, take off the oil cap and look (with a light) inthere if the cam is beiing lubricated? Then// all is well! (as it is the highest part to be lube'd

We did install a new oil pressure sender. Let me check the cam lobes today when we start the car. I think last time when installing a new cam we did a remote start with the valve cover off and did see the oil coming out of the cam holes. Mine doesn’t have a spray bar etc. but will verify again.

To put your mind at rest, when cold, mine starts over 3/4 across when reversing out of the drive way and normal driving. When it warms up, it sits near a half cruising and over half thrashing it.

At idle it can go below 1/4.

The oil itself does flow better and therefore less pressure when heated. So in some ways, the drop in the gauge is what I use (in the absence of an oil temp gauge) to know the engine / oil has reached full working temp.

I needed a change of underwear when running the engine in as the oil pressure went to zero while doing 70mph. I shut it off and pulled over VERY quickly - only to discover that the connector on the sender was clicking on, but was loose and had corrosion inside of it. Cleaned it up and bent it back into a shape that made it stay in contact, it’s been flawless since.

Before looking at the wiring, I did exactly what has been suggested - I took the oil filler cap off and started the car to observe oil sloshing around the inside of the cam cover.

Don’t panic, we’ve all been there - but you’re wise to question it and do the checks also.

It is possible to hardpipe an oil gauge in at the oil sender to get a direct pressure measurement

Yes, it's possible. And that is what I would recommend to the OP if he's really wondering what the numbers really are.