That plus change the oil to a better quality??? and or higher grade. Grade 5-??? what ever is the norm in the winter may not be good enough in the summer. I use 15-40 all year round and the oil pressure never falls below 30 PSI when hot and at idle.
If he can confirm that he has 0 psi with a mechanical gauge then I think his problems are beyond what can be helped by running thicker or more expensive oil. It would either be an issue with the pump or bearings, maybe the oil filter if its a fram. He does have a 2001, so it is possible the head is cracked and coolant has been getting into the oil. Over time that would wipe out the bearings and cause low oil pressure.
But he says it will have 10 psi one day and 0 the next. To me that sounds like an electrical problem in the sender/gauge circuit, or possibly sludge buildup within the engine blocking oil passages intermittently. If he truly had 0 psi he'd probably have knocking lifters and connecting rods.
Things I would verify:
-Adequate oil level in pan.
-Oil filter is not fram. Something like Wix, Mopar, K&N, etc.
-Actual oil pressure w/ mechanical gauge
-No excess sludge buildup (pull valve cover). If there is much sludge, try flushing the engine.
If low pressure is confirmed by the mechanical gauge and there is not a sludge problem, the next step is to check the bottom end.
Also, I would not drive it until I had confirmed it had acceptable oil pressure. If for some reason it has actually lost pressure, it might still be possible to fix the problem by replacing the pump and/or bearings, without doing a full rebuild. If driven to the point the rods are knocking, it gets more complicated.