I have been using motul 300V in an older xr250r the reason being to keep oil temps down (this model cracks heads when thrashed) 300V is very expensive out here (New Zealand). I was going to switch to yamalube fully synthetic 10W40 which is cheaper but I have a little motul left I'd be mixing 1L of motul and 600 of yamalube or similar (possibly the other way round). How would this work out? Are there dangers??