I just rebuilt a 3VZ and replaced it with my old one in my 95 4Runner. It purs like a kitten, but the oil pressure drops off as it runs longer. I start it up in the morning and the oil pressure comes up to normal at idle and then as I drive it to work the pressure drops off and doesnt come back up even when I stop at lights. I used a new Valvoline filter and 10W30 oil. I put a new oil pan gasket on it and the pick up screen was clean and clear of debris (from what I could tell). It has a sending unit with about 135,xxx miles on it and it has been untouched by me since I started the rebuild. Does anyone have any ideas as to what could be causing this?

 

The oil pressure drops off because the oil thins down as it warms up. The 10 million dollar question is: How MUCH does the oil pressure drop off? Keep in mind the factory gauge and sending unit have bad reputations ... do some searching on here. Check it with an aftermarket gauge and see how it reads.