So I've got as far as 'I should get fully synth'. Now I have the problem Kawasaki say use 10w/50 Castrol say if that's what Kawasaki recommend they *ought* to be right But on the shelves it all seems to be 5w/40 and asking for 10w/50 I get told by the bloke trying to sell the stuff 5w/40's better. Yeah well, better for them to sell something is obvious. But beyond that why? I thought 10w/50 would be better for protecting a hot motor. OK 5w will give a bit more protection from cold but being a wuss and hating salt I don't usually ride when its *really* cold, beside it lives in the garage. So why's 5w/40 so popular and recommended grade isn't? -- Nidge ZX6R J2 Stunning in zit yellow. KX 125 MX 'I'm snot green -fly ME'. A few bits of CB500S in Norwegian Parrot blue. BOTAFOT#63 BOMB#5 'Just because I don't care doesn't mean I don't understand'. Homer (Simpson).
Does your manual not give you a breakdown of when to use what? In the GSX-R manual it lists the grade to use based on ambient temperature. ARAIR, using 10w or 5w will be fine.
You'll also find that there's a large overlap too. Personally I like using 10w/40. Having said that, the FJ owners club recommend 10w/40 for the winter and 20w/50 for the summer.
How much hotter does a water cooled engine get in the summer ? All this about different oil for different climates makes a lot more sense for air cooled engines. At the cold end, both 5W and 10W are fine as long as you don't do cold starts in true arctic temperatures.
It does a little, certainly nothing like the air cooled lump does though. Yes, as a rule I'd just stick to a 10w/40, it's the best sompromise, and I doubt you'll ever find out the difference anyway. You only really need to worry about viscosity if you are going to use the machine in extreme conditions - such as racing or arctic.
