first start break in

The air release hole in the t-stat is a good idea and as shown, some stats come with a bypass. You can use water for break-in but antifreeze has a higher boiling point. Water's boiling point is 100 C = 212 F. Straight ethylene glycol's boiling point is at 197.3 C = 387 F. Of course, you shouldn't use straight ethylene glycol in the radiator either for the sake of efficiency. Because it is a new engine and hasn't been thoroughly tested with water in the system, you can drain it out, repair leaks, and refill without wasting any coolant. Or you can fill it with a 50/50 mix and catch it in a pan if you need to drain it out. You should always use a good radiator cap also if you are concerned about overheating. For every pound of cooling system pressure it raises the boiling point 3°. A 15# cap will add 45° to the boiling point. tmm