hey.
want to hear a good one, as i haven't been here in a while either,
let family members run my 19' boat and f'ing drain plug falls out of the pan. this was back in august, pulled the motor and had it rebuilt. They started losing power then shut the key off before the motor shut itself off. One rod bearing seized, and locked up the motor. Pulled the motor, pulled pan, could tell which rod bearing it was so as soon as i undid that the crank spun and the other 3 pistons went up and down no problem- this was running an engine without oil till it basically siezed. I could have probably just replaced that bearing, through some 15w40 in it and been running again.
so I have first hand experience and i can send you some nice pics of the 3.0L, it's a 2001 block, hecho en mexico.
you will never never never ever ever get over 40 psi +/- a few because the oil pump is a ( melling m-62 if my memory is correct) and when i put the new pump in and spun it up with a priming tool through the distributor, max pressure is 40-50 psi with a mechanical gauge- because the relief spring in the oil pump lets go at 40 psi. I also bench tested the old oil pump with an air hose and regulator for kicks, same deal.
so knowing that, you can gauge pressure vs rpm vs oil viscosity and know whether a heavier or lighter viscosity oil is what you might need. If you get 40 psi on your gauge at 1000 rpm, then you don't *need* a heavier oil, if it takes 2000+ rpm then probably a thicker oil might be beneficial.
I was running delvac1300 15w40, and continue to use it. For the price, it's the best oil. plus, it's a flat tappet motor so you want an oil with zddp or good AW adds for the cam/lifters so stick with a 15w40. The shop that did my motor even had a pamphlet from aera indicating the lack of antiwears (zddp) in API-sm oils and a strong recommendation to use 15w40 oil in flat tappet engines, specifically mobil delvac, chevron delo, rotella, and the shop i used swears by napa fleet 15w40.