'89 360 -- replace bearings or not?

I recently bought an '89 B250 with the port-injected 360 gas engine. The van is in nice shape, and seems to have plenty of pep. Problem is -- low oil
pressure. I replaced the oil pump with a new hi-volume one, and installed a good mechanical oil pressure gauge. It would read around 60psi when I first started it, then, after 15 miles, if I came to a stop with the transmission in gear, it would be down to 20psi, and after another 25 miles or so, if I came to a stop, pressure would drop to zero and the van would stall.
I tried replacing the oil with 20W50 synthetic, and that's helped a bit. After extended driving, it now only goes down as far as 20psi (again, trans in gear, foot on brake).
My mechanic says I shouldn't drive it with that heavy oil during the winter, and recommends replacing the engine bearings. He says he can put them in from the bottom without pulling the engine, so it shouldn't be TOO expensive.
I don't mind spending the money, but don't want to spend the money and find myself in the same situation when we put it all back together. I've never put new bearings into an engine without simultaneously cutting the crank, so I'm not sure if just replacing the bearings is really sound practice.
Thanks.
Joe
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You can replace crank mains and rods from the bottom, no problem. Further, its an acceptad practice, and done correctly, causes no problems. However, I'd bet on the cam bearings as being the problem, and as such, you might as well pull the cam and do them to be sure to solve the problem.
JMO, YMMV, but don't expect the crank bearings to solve this problem.
Also, I see no problem running the 20w50 in winter, so long as temps are not extreme. If you live in Canada, heed your mechanics advice. If temps regularly go below 10F, simply changing viscosity for the winter may still solve the pressure problem. Ultimately, you'll have to rebearing the motor.
AS far as cutting the crank, this depends on amount of damage, and can only be correctly assessed by pulling the bearigns and lookign at the crank. If its too much, you'll end up pulling the engine.
--
Max

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