^^^10w40 or better. JASO Ma or MA2 preferrably. Brand is immaterial.
The only Castrol 4T oil viscosities I've been able to locate are the 10w40 and the 20w50.....hey guys got a 2004 vl800 im currently got castrol 4t 5-40 in her and want to know how goood that is or is there anything better?
Straight weight oils do not have the problems associated with viscosity modifiers5w40 is too thin. The viscosity modifiers cannot withstand the shearing caused by the shared bath transmission. Your oil will perform worse than a 20 wt in short order as a result. Drain that crap out and put in the recommended oil. 10w40 or better. JASO Ma or MA2 preferrably. Brand is immaterial.