Oil Pressure in 98 Isuzu Trooper 3.5L 6Cyl, 96K~ mileage

First thing I would do is attach a manual oil pressure gauge to where the oil pressure sending unit screws into.That way you could verify that you don't just have a bad sending unit or faulty gauge.
If in fact it is the true pressure then I'd wager your getting ready to spin a rod bearing. Mine did that at 98,500.
Playing with the viscosity of the oil will probably raise your gauge readings but ultimately due more damage to your engine.
Good Luck
Dale

You will find that your engine will need a overhaul. You said oil pressure is good when cold. If it is below 75 at a idle cold and 35 on a fully warmed engine then you are looking at a melt down. Very possible the oil pump is going up and again overhaul will be necessary because if you are going to do all of that work you might as well do the rest because it will not be long. After repairs are done change your oil and filter every 2 moths and or 2000 miles or so. I know what they recommend but for most drivers 3 months or 3000 miles is too long. And most people get rid of their cars after 2-3 years and then it is another owners problem. These engines run hotter and not like older cars of days gone by.

Fred