*Tech Talk* Low-viscosity Oil in 1NZ-FE

[Lux]

Hi Yaris World

I have a few technical questions for the gear heads around here. This is intended for highly experienced service technicians and engine builders.

I am experimenting with the use of low-viscosity (0W-20, 5W-20) motor oils for my 1NZ-FE engine for further reduction of parasitic loss (short of knife-edging the crankshaft). I want to ask for some information regarding the mechanical limitations of the NZ engine's lubricating system. My main concerns are with the oil pump, journal and bearing tolerances, valvetrain, VVT-i phasing, and changes in oil pressure.

I know that, by design, the engine is intended for the use of 5W-30. What I'd like to know is whether the journal/bearing clearances will tolerate thinner oil under all conditions... I'm talking about cold start (dry bearings) to extreme-duty race loads. Chemical thermostability is a non-issue as I will use full synthetic oil.

Will the cam phaser be affected by a low-viscosity oil? Has anyone noticed the engine knocking on a cold start (zero oil pressure) due to inadequate viscosity? Any further insight into using 20-weight motor oil on these engines?

This isn't isn't a typical drain & fill question, I'm interested in the science behind viscosity versus the NZ sump system.

Thanks!