Any of the things you mentioned are possible. At the mileage you listed the bearings could have enough wear to allow the pressurized oil to run out through them too quickly resulting in low pressure. You may overcome that by using a thicker oil at the next oil change. The wear can be due to high mileage, which is not catastrophic, or it could be due to a momentary loss of oil flow that caused the bearings to be chewed up and rough. That kind of damage will continue to tear things up and is not likely to last two weeks. The bearings and crankshaft can be replaced but since the cause of the damage is oil-related, and oil protects many other parts of the engine, that is usually why engines are totally rebuilt. The crankshaft and bearings don't fail on their own. When they do fail, the cause is related to so many other parts and those are likely to have suffered damage too that will get worse quickly if ignored. A total engine rebuild addresses all of those things.
Start by having your mechanic check the actual oil pressure with a mechanical gauge. If it is okay, suspect the sending unit. If it really is low, try a thicker oil.
Monday, September 2nd, 2013 AT 12:46 PM