I have a 1991 BMW 7 series with 140K that runs great. For the last year after the car has been sitting a few days and I do a ‘cold start’, the oil light on the task takes about 10 or 11 seconds to go out. Then I receive a message in the dashboard to ‘check the oil pressure.’ I have had my oil changed 3x since then, and the oil amount is correct. I switched from a 10W-40 weight to a 10W-30 weight, thinking that would help, and it didn’t make a difference. The BMW dealer replaced the oil switch under the dash, with no change. My BMW specialist thought it might be something where the valves were, and tightened a screw (?). However, no change. Does anyone have an idea? Also, this only happens on a cold start when the car has been sitting for 2 or more days. Other than that, the car runs great and I took it last week on a 900 mile highway trip without problems. Thanks!
Oil pressure and oil level are two very different things. The first step here is to connect a mechanical oil pressure gauge to the engine to determine if the oil pressure is too low. If it is, then the two biggest possibilities are a worn out oil pump or a worn out engine.
You might need a better quality oil filter. If the anti-drainback valve on yours is leaking, the oil pump has to refill the whole filter before it can start circulating oil to the engine.