I know you're supposed to use 5w40 oil in the bmw, but can you just use 10w40 oil? It's not like i'm starting the bike up when its sub zero temperatures outside. just wondering if this would damage the bike as maybe the tolerances are extremely tight on these bikes and perhaps 10w40 oil would cause too much oil pressure to build on a start up.
I use 10w40 Amsoil when the temp gets above 80 when starting it up. I called Amsoil and they said its fine to use even down to freezing but in the winter time or when below 80 i use Castrol power 1 5w40. I do think the Amsoil protects better when hot out sense these bikes run so hot to begin with.
"In a 10w-40 for example the 10w bit (W = winter, not weight or watt or anything else for that matter) simply means that the oil must have a certain maximum viscosity/flow at low temperature. The lower the "W" number the better the oil's cold temperature/cold start performance.
The 40 in a 10w-40 simply means that the oil must fall within certain viscosity limits at 100°C. This is a fixed limit and all oils that end in 40 must achieve these limits. "
I did not know that the "w" literally meant "winter".