A year ago, my oil light started coming on after the vehicle runs for about 10 minutes when idling. When the RPMs increase, the light would go out. My local garage replaced the oil sender unit and the light went out. About a year later, the problem came back. Is it necessary to fix this again, or can I just let this go? I wish to replace the vehicle soon, but I also would like to keep it around for a few months. What could possibly happen if I dont fix it?
This happens with older cars that have low oil pressure due to worn out bearings. I suspect you had a marginal oil pressure sender that was triggering at the wrong time, and a replacement fixed that. But, it is possible the wear continued and the idle pressure continued to drop until, now, it is getting very low.
To get a little more life out of this car, start using a heavier weight oil. If your using 10W-30, try 20W-50. The thicker oil will hold the pressure better until your ready to replace it.
You need to have your mechanic check the actual oil pressure with a mechanical gauge while the engine is warm. This will tell you whether the sender is bad or if you have a more serious internal engine problem developing.
Has the oil been changed regularly on this vehicle? Has it ever been run low on oil?