If there is one thing a rider has control of its the viscosity of
their oil... chemically speaking either the 30 or 40 will meet and
exceed your mileage expectations... BUT according to Honda it is best
to use the freer flowing 30 over the slower flowing 40... engineer
tested the freer flowing 30 lubricates and cools critical engine
components better than slower flowing 40 oils can. Freer flowing oils
reduce bearing temperatures and sump temperatures compared to slower
flowing 40. Freer flowing 30 can also help increase horsepower and
miles per gallon.
I run a 30 grade all year because it gives the right flow at the
normal engine operating temperature of 212ºF and that would be the
viscosity of 10 at operating temps... so that means for every 1000
rpms increase of oil pressure increases another 10 psi... a 30 grade
flows more oil at higher rpms which flows more oil between the
critical bearings which carries away more heat and I'm not wasting HP
just pumping oil through the blow off valve... 40 grade builds pressure
at the expense of flow and I wastes HP by blowing oil through the
pressure relief valve...
30w psi
1000 10
2000 20
3000 30
4000 40
5000 50
6000 60
7000 70
8000 80
9000 90
10000 99
11000 99 blow off by the pressure relief valve
40w psi
1000 12
2000 24
3000 36
4000 48
5000 72
6000 84
7000 96
8000 99 blow off by the pressure relief valve
9000 99
10000 99
11000 99
RC45 coolant 203F oil 10 psi