No this is not a which oil is the best thread.... I want to try a different type of oil for my bike to see how it goes, as currently its running off Motul 5100 10W50. Anyway after checking the owners manual it says it supports 10W-40/50 & 20W-40/50 which would be suitable for up here in QLD. So I went researching and others a bunch of oils and the only one I could source locally was Shell Advance SX2. After speaking to one place that stocks it they said they have 20W-50 of it in stock. To keep things short, I go to the shop and not until I have paid for it do I notice its 15W-20! Now my bikes manual doesn't mention 15W at all but the dude at the bike shop says they run it all bikes they work on in their workshop. Reading the back Shell says its for all 4 strokes. So how bad would it be to run this oil in my bike even tho Kawasaki doesn't specifically reference its (ie 15W-40/50)? I notice that 20W oil seems to be hard to source with 10W & 15W fairly common. Anyway thought I'd ask here to see what everyone rekons. Also my bike has over 40k on it and I am lead to believe running 20W oil is better for an old engine than 10W. Would 15W be a good middleground (as far as viscosity is concerned, not too thick not too thin)? Or doesn't wit work like that? Thanks. Disclaimer: I don't know much about bikes so please be kind.