If you mount it above the motor you will get better air flow and you will avoid air getting trapped when filling the motor with coolant. Your radiator will also be less prone to get damaged by the prop kicking stuff into it. I mounted mine on the back legs of my engine stand and my motor runs 160 with no trouble but I use a cooling fan when I am bowfish or the temp will climb to 180. My friend mounted his up top and his motor runs way cooler then mine plus he does not need a fill can now.