[wedser]

I would say from what you are describing you have a very high mileage engine. The bearings are wearing a lot, and that extra clearance allows the oil pressure to drop. (pressure is defined as resistance to flow, the less resistance i.e. more bearing clearance, the less pressure). Also the hotter the oil gets the thinner it gets, also creating less resistance to flow. A simple but temporary cure would be to step up the grade of oil you are using to 10W-40 or even 20W-50, and then re-build the engine.