Low Oil Pressure on Start Up

Hello,

I have a 915is on my plane. Very powerful engine on the flight. But the oil pressure is low during the startup procedure. Oil pressure is dropping the 0.5 bar after the engine starts from 2 bar, step by step and waits here for 20-30 secs. After 20-30 seconds, it rises back to between 1.5-2 bars. The oil pressure is rising with the oil temperature. When the oil temperature is 50 °C, the oil pressure is 3 bar. I have been using this engine for 2 months so the ambient temperature is 1-2 °C when the engine start. All of this procedure, the engine is turning 1800 rpm.