True - but there is more to it !!!!!
That big rectangular box on the top on your engine-- the one with the eyebolt in it is a large open water jacket. The YSE, YSM ands YSL all have a huge water capacity around the cylinder sleeve. They also have some small ports (about 3/8")from the head to the engine casting, Water enters the head at the "T" connection from the pump and fills this water jacket through these ports. Water then exits this chamber through the thermostat and mixes in the thermostat housing with by-passed water, which then flows to the mixing elbow. I found these ports to be nearly plugged with rust in fresh water use-- The only way to clean them is to remove the head clean and flush-- You might consider back-flushing the system through the thermostat housing. --BE SURE TO DISCONNECT THE LINE TO THE MIXING ELBOW-- or risk flooding the valves with water. Adjacent to the thermostat is a plug in the same water jacket-- this is the engine zinc-- change it, and check it often. If you experience engine overheating, -- I notice many posts on here concerning engines of this vintage about -- "after a half an hour my engine runs hot and .........."- and beyond the obvious responses concerning pump impellers, intake blockage and thermostat lock-up, the configuration of the head porting seems to me an overlooked item. Blockage of these ports will cause the severe coke generation, valve warping, and mixing elbow buildup you may have heard so much about. If you experience any of the above problems or see indication of them -- a build up of carbon on the intake pipe is a big indicator -- pull the head and clean the jacket ports. The good news is that removal and replacement of the head on this engine is simple and can be completed without engine removal. Terry
