which gearbox oil should i use?

[defibros]

I go royal purple!!!!!I had it on my skylne and Wrx before and it's awesome!!! Even the engine oil is great !!!just a bit pricey

[aaronng]

I go royal purple!!!!!I had it on my skylne and Wrx before and it's awesome!!! Even the engine oil is great !!!just a bit pricey

Royal Purple may be great for other gearboxes, but those are spec'd to use 75w90. Honda uses 75w80, which is a grade thinner when warm. Interestingly, I have compared both Royal Purple and Honda MTF from the bottle and the Royal Purple was like warm honey, while Honda MTF was like slightly thicker cooking oil. That is a big difference in viscosity eventhough this was at 20 C and the 80/90 viscosity is measured at 100 C.