overheating and exhaust from prop

[clickmaine]

Hello..I have a mercruiser 260 with a overheating problem at idle. new risers, manifolds,thermostat,thermostat cover, new pump in drive,circulation pump. Is it posible for the Y-pipe to be pluged and causing my overheat problem? I had the drive in a test tank and noticed there were no exhaust bubbles being made.The only exhaust was comeing from the 2 smaller holes at the bottom of the gimble. I back flushed the Y-pipe and could get water to come out the smaller holes but not the prop.