[wolfrpi]

Mine wouldn't drop at all. It would pretty much peg 5 bar and stay there until 7000 rpm. I'd check your compresssion first on all four cylinders (its quick and easy). If its bad (significantly less than 150 psi), you're in big trouble. Also check your voltage to the oil pressure switch and the related grounds. Check the tightness of the crank pulley also. Finally, use 20-50w to protect it in the future.

Erick