As I recall the conventional wisdom is that the maximum antifreeze mixture for a Yanmar thermosiphon cooling system is 70-30. That gives a freeze protection of 7 deg F, which is borderline for my area. Therefore I have been keeping mine at 50-50, especially for winter operation. The last year the engine temp has been up to 130 when mowing. When it started to exceed that regularly I figured I'd bite the bullet and replace the radiator (after a local radiator shop's repair quotes bracketed the cost of a new one). Because winter is approaching, I put in a 50-50 antifreeze mixture, with a dose of water wetter. The operating temp has been around 205 since then. I figure that is safe. For that matter, I figure 230 is safe since the OEM idiot light sensor trips at a reported 238 or thereabouts. Anyway, the question is: Will a weaker antifreeze mixture drop that temp significantly? I have heard reports that some of these engines run at less than 190.