Problem with oil light coming on after 20 mins or when motor warms up on a Mercedes 420SE?

Car is 1986 model and runs leaded fuel.Problem with oil light coming on after 20 mins or when motor warms up on a Mercedes 420SE?
similar problem in past. hate to say it , but probably low oil pressure, especially since you say it goes on after engine warms up ( as metal parts heat up, they expand slightly, thereby increasing critical clearance specs between bearing surfaces.) oil pressure, compression should be checked now before more damage occurs, good luckProblem with oil light coming on after 20 mins or when motor warms up on a Mercedes 420SE?
You should check to see if you have the proper amount of oil in your vehicle. With the vehicle off, and at operating temperature, check the dip stick. You should pull it, wipe it clean, stick it back in, and check it once more. If the oil level is fine you may have a different problem, perhaps clogged oil filter, oil leak, or something causing a change in oil pressure enough to exceed the parameters set by your warning lamp. I'm not familiar with your specific make and model but some cars also share an engine and oil lamp in which case it could be any number of problems. Far too many to list. I recommend keeping an eye on your coolant temperature as well, as engine temperature and oil related conditions can be directly related. Above all though, I recommend taking your car to shop to assess the severity of the problem.
Try this Turn the key when the lights in the car turns on then press the gas pedal like 15 secs. I think and it should turn off.