Buick Apollo Oil light Flickiring when HOT.

When Temp raises to 65 the light of oil on the dash start to flicker on low RPM. when u raise up the RPM it turns off. what is the problem ? Oil pump? sending unit or what ?

 

Check the wiring for the sender and the ground to the light/PCB for the cluster.
If there is any open, the light will come one. And a loose connection can become intermittent with vibration (RPM) enough to be hard to pin down.
If the wiring checks out, change the sender. It's a $15 part, and it either fixes it or it does not.

I had a new oil pressure sender go soon after break in.

About 100 miles on new engine, I was adjusting timing and carbs, and with the hood open and about 95 degree day, about 30 minutes of idling, I noticed I was about 230 degrees, and the temp light illuminated and the oil pressure light started flickering, but pressure was still about 25-30*.

I put a high velocity shop fan in front of the car and closed the hood, brought RPM up to 3000 and the temp came back down with in a minute to about 215, and I kept it there for about 5 minutes and then shut down. Oil pressure was up to 43 (the normal for this engine) at 3000, so I believed the gage was working and I had pressure, but the oil light was flickering.

The next day I fired it up and the oil light stayed off, so I was a little concerned that maybe the gauge was not true, put another gauge I had from my other 'lark, and it read the same, and I took the car for a drive. When I got back and was backing into the garage, hot oil pressure was about 25, and coolant temp was about 210 (another hot day) and the oil light flickered at idle, (engine idle is about 500-550) and then it came on and stayed on.

I let the car sit overnight and next day, cold started, 43 PSI (still using the second guage) and the oil light was on. Pulled the wire and grounded it and the light went out.
Replaced the sender and 6 months, 600 miles later, hour long highway and heavy stop and go all summer long, no more oil light.

Even and engine overheat, should not cause the sender to fail, so I think it was marginal/faulty from the start, and the heat just helped it fail.

On a new engine, dealing with a vacuum leak and a self induced problem that killed 2 coils, I was dealing with more variables and the oil light was baffling. (I have never, in 45 years, seen this happen).

 

Usually thats an indication of low oil pressure. when the oils hot it thins out and the pressure drops below the min set point of the switch at idle / low rpm. Could be worn cam bearings, but most likely the oil pump pocket in the timing cover is worn.

 

If it has the original timing cam gear the plastic comes off blocking oil pickup screen.