Now, take that at face value. You have an engine spec'd for 5W-30, so an HTHS of around 3.0cP and you are running an oil with an HTHS of 1.58cP. Do you think the bearing clearance selection for this engine was based around a 1.58cP HTHS?That is a nice summary of one portion Zee. Bring it into the whole paper. The bearing clearance tighter lifts the MOFT. If you read it in whole there is an optimum viscosity to the oil clearance. Tighter bearing clearance, lower viscosity oil is optimum. Read paragraph below figure 3.