I run 5w20 in my 250, year round, but don't drive every day. I have seen the effects of thick oil on oil pump drives and cam gears.
I am going to have to disagree with the meter holes mentioned above. 10w30 will flow through a meter hole at low temps like 10 w oil, this is true, but at higher temps, it does thicken up to 30w oil, what it does is lubricate like a 30w oil due to it chemical make up. The viscosity always stays the same.
Joe
