01 4.7 oil pressure gague drops at idle

01 4.7, 170k miles. Today, sitting at a stop light for about 10-20 seconds, hear a ding. Check gagues light was on, oil pressure gauge reading on the "L" line. As soon as I put it in neutral, it popped back up to the first line on the gague. It's done it to me a few times. It was a little low on oil, OK two quarts! even after filling it back up, it's still doing it. The engine makes no funny noises, even when the gague is sitting at the L. Any ideas? Thanks!

If it's easy and cheap, swap out the sending unit. Otherwise hook up a gage and see what the actual pressure is.

My 03 a few times this winter would show 0 oil psi on very cold mornings. I have 221k on it and have heard the oil psi gauge is not really a gauge but a fancy idiot type light/ gauge which explained why in all that mileage the needle is at the exact same spot no matter temp or oil viscosity. If it bothers you I would replace the sending unit.

An inexpensive AP store mechanical gauge is a low cost diagnostic. 170k is a fair amount of miles also... bearing clearances may be on the high side. Heavier oil may help if pressure is dropping below 10 or 15 psi at hot idle. 15W40 diesel oil or 20W50 car oil may keep it going.

The thing is that it's not a constant thing. It happens when the engine is hot, but I just took it for a drive, got off the freeway, and it didn't do it. Idled through a parking lot, and it did when I stopped.