My old pontiac 6000 did that, and my dads chevy van (350) does that. Both are NOT because of the oil pump. the 6000's rod bearings were shot, and let the oil pressure out WAY to fast. eventually, it threw a rod.
The van's main bearings are loose, and it runs fine, but it also lets too much oil out of the lubrication holes. My dad installed a high volume, high pressure oil pump that now pushes 60-80psi (!!!!) at revs above 2000, but at idle, it still has trouble getting it above 10 psi while warm.
The van's main bearings are loose, and it runs fine, but it also lets too much oil out of the lubrication holes. My dad installed a high volume, high pressure oil pump that now pushes 60-80psi (!!!!) at revs above 2000, but at idle, it still has trouble getting it above 10 psi while warm.