I had a 99 Chevy Malibu with the 3.1v6, one day I was heading somewhere about 10 miles away. Got about 5 miles and suddenly the motor lost power and was making a terrible noise. Pulled over immediately and had it trailered home. Oil pressure sender had spewed all but a half quart of the oil out. Used a cleaner that contained kerosene in the oil. Then changed oil and filter and sending unit. Engine was fine only valve train chatter when cold.
A couple years later was heading home from a out 50 miles away, got about 10 miles from home and lost heat then temp climbed. Stopped and filled it with water and carried on. About 2 more miles and no heat again. Got it home carefully without overheating it. Made appointment the next day for a head gasket. Shop said they won't do it because bearings are shot. Couldn't get any local shop to do the head gasket because "bearings are shot". Literally I drained 4 gallons of light brown pudding from the motor. Sprayed out under valve cover through the filler hole with carb cleaner the best I could and changed the oil and filter twice.
Gave the car to my dad last year and he is now about to get the head gasket changed by a co worker. The car hasn't been driven far but is started regularly and shut back down before it gets hot. Still just the valve train chatter when cold. Other than that it runs great and has great power. Sorry for the long post but I wouldn't be so quick to say the bearings are shot. Although I haven't had that same experience with a 4.0 but I'm betting they're tougher than that 3.1.
