I switched from Dino Shell 10W40 to AMSOIL 5W40 and my oil pressure dropped! After I changed oil and filter I took the car for a drive. When cold Oil pressure was around 5 bar. Drove for 20 min to bring the oil temp to 100.C At 100c the pressure was about 2.5 bar @ 3000 rpm However; At idle the pressure drops to 0.5 bar and my dash oil light comes on. This did not happen with Dino 10W40!! What could be causing it? Is AMS 5W40 has lower viscosity than dino 10W40?