splitpost
Nothing but 32:1
May sound silly to some of you guys but i use 85w/90 gear oil, i have the pump turned right down 2.5-3 tanks of fuel to 1 tank of oil, now as this oil is so heavy, not designed to be burnt and about 4 times as tacky as light engine oils , what little oil i am using seems to stay where it is meant to be. Works great, my advantage is an endless supply on tap that seems to make it to my place for free, however in saying that, diff/gear oil may not work out to be an expensive option as you seem to only need to use so little of it by comparison. The only area for concern is if or if not stihl would warrant a pump pumping oil of this weight, who knows, but a 460 and 660 do it with what seems to be ease anyway.
iv'e tried gear oils before and agree yes they work well and don't smell the best and if you compare it with the heavy duty stihl oil available ,the one with red cap it pretty much looks the same when pouring it out of the container ,it too is thick and glugy,as for you guys using caltex B&C lube will already know ,it smells a bit like gear oil ,on cold days maybe it is too thick and could be thinned down but on hot days with long run times they all turn to the same viscosity as water.
Disclaimer(all these observations were taken using my eyeviscometer)