2001 115 four stroke yamaha

Ok my alarm is sounding on cold start and oil light comes on, just when i take it to the boat ramp, never does it in the drive way with the hose on it.changer the sender installed a tee so i have the sender and oil pressure gauge you know it did not do it this time out I am running caster oil GTX oil it all started after I stoped using yamaha oil any one found this to be a problem.

Is the oil vescosity the same? I know that people don't like to hear this but Yamaha is not an oil refiner, so someone else is processing their oil then filling their jugs. I have had multiple mechanics, that think for themselves, tell me that the most important thing is weight not Brand.

My 115 gives off an alarm almost every time out. I shut it off and start again and no alarm. I don't know what it is but it is the only trouble I have ever had. Starts every time and no other problems. I can live with a restart. That's just me.