Which Is The Best Oil For Maintaining Hot Viscosity?

True of some but the T150/160 runs a gear pump and will easily make 100psi + on cold start and should see around 10-20psi at idle when hot,
but IMO oil quantity/flow and film retention under running pressures is just as important.

 

Got some Millers 20w60 and changed the oil yesterday ...took it for 7 mile run to get some fuel and it seems to be holding good pressure and its usually reasonably hot after that so so far so good....think there was a little fuel contamination which wasn't helping.