The 4510 has 2 screens to keep debris out. One in front of the radiator and one behind. The one behind is almost invisible. We had problems with one and kept cleaning the front screen. It would help to keep the engine cool but the air conditioning wasn't worth a crap after an hour or so of running. Finally after some time found out about that rear screen. Problem solved and haven't had a minutes trouble since out of that machine. It really is hidden back behind there like a ninja. I figure that somebody already checked this but sounds like your symptoms are very similar. We laughed at ourselves pretty hard after hours of scratching our heads looking for problems with the cooling system. Maybe you will too. Good luck.