Low oil pressure is caused by lots of things, but start with the filter first.
I own an 85 Olds Delta 88 with 83,000 miles. It is well-maintained and has its oil and filter changed regularly. For the last couple of months, the oil light either comes on or flutters when I'm stopped at a traffic light or when I'm going up a hill. The oil level is always OK. I had the oil pressure checked, and the mechanic says it's OK, although he says I was using the wrong filter. Several filters later, it's still happening. What could be causing this problem?
RAY: It certainly sounds like low oil pressure, John. Your mechanic may have tested it, but he may not have done it correctly.
TOM: Low oil pressure can be caused by several things. You could have old, worn out bearings, a bad oil pump, or a plugged oil screen. My guess is that you have two of these problems...if not all three.
RAY: The low oil pressure at idle is probably caused by either bad bearings, a bad pump, or both. A "leak down" test will tell your mechanic if the bearings are bad. If they are, you're going to need an engine rebuild. If it's the pump, it's only a few hundred dollars.
TOM: The low pressure on hills is more likely to be caused by a plugged oil screen. But they'll fix that when they rebuild the rest of the engine.
RAY: By the way, it's unusual to have any of these problems if you've been changing your oil regularly, as you say you have. But you don't say what "regularly" is for you.
TOM: Right. I floss regularly. To me that's once every six months, just before I go to the dentist. And if your definition of "regularly" is like mine, you may have contributed to this condition.