Looking for water impeller fragments.....

[Mike Raehl]

Hi to all,
My sailing buddy finally replaced the water pump impeller on his Yanmar 1GM 10 engine after the temperature warning light activated. With a new impeller, there is more water exiting with the exhaust but the temp warning light still activates after five minutes running time. The old impeller was missing some vane pieces so I suspect the fragments are blocking water flow around the cylinder head or the thermostate is faulty. Replacing the thermostat is easy enough. Question is how to locate and remove any impeller fragments or blockages from the engine block? My thought is to remove the thermostat and external water hoses and then backflush water or air through the engine using the thermostat cover as the water input point. Exit points would be the engine drain valve, the water pump hose, the temperature sending unit mounnting hole and the zinc mounting hole. Am I on the right track or are there better ways to probe inside the engine block?

This engine has always been in fresh water.

Thanks for any suggestions.

[Oswego John]

Mike,

As you say, there is more water passing through the engine than there was before. That suggests to me that some parts of the engine are cooler than other areas. There is a good chance that some water passages might be blocked off by pieces of the impeller.

There is one way to locate the area of the engine that might lack sufficient coolant. Try to borrow or rent a laser, infra ray, non contact thermometer. Home Depot and Lowes sell a Ryobi unit for under $30.00.

Yes, it is a good idea to try the easy things first. Back flushing might solve the problem. If not, then locating the hot area(s) might save tearing down some parts of the engine.

Good luck,
O J