99 lumina oil light

I have a 99 lumina with a weird oil light situation. I am also a mail carrier and I use my own car so I do alot of stop and go. I changed the oil and filter on July 4th. The very next day the oil light came on after I had driven it for awhile and then stopped. Once I hit the gas it went off and stayed off until I stopped again. So I took it to the shop and they said it was probably the sending unit so they replaced it. They started the car and let it ran at idle for about 30 minutes and no oil light came on. The next day I'm out driving and it came on once when I was stopped and then never came on again the rest of the day. The following days it gradually went back to coming on when stopped.

Now the weird part is that it only comes on when the engine is very warm I would say around the 180 to 200 mark. My gauge only has 100 and 260 mark sand the needle is right in the middle. Normal driving(not alot of stop and go) it never comes on, but once I start delivering mail and the temp starts to build it comes on when I stop and off when I go.

Also they engine runs very quite. No pinging or anything

Now once I am done with my route and start driving regularlly and the engine cools down it doesn't come back on going or stopped.

Any thoughts would greatly be appreciated.

Welcome to AF. Have the oil pressure tested under the hot operating conditions using a mechanical gage tapped into the sensor port. Also 3.1 or 3800?

What weight oil did they put in? It sounds like the oil is thinning out as the engine gets hot, and the type of driving you do is definitely considered extreme.

3.1 ltr and I put 10w 30 in. What gets me is that before the oil change there was no light and after oil change it comes on.

If I were to use a heavier oil would it be hard on the engine when cold starting in the winter. It doesn't get really cold as in below zero but sometimes it will dip into the single digits.(ky)