Impeller Change Procedure Review
Now that users have an idea on what time is best to change impellers & clean internal engine water passages, why not share a technical explanation with those boaters who haven't seen how an impeller looks, works and the procedure & tips to change them if sufficient skilled.
Although all impellers performs the same work, that is refrigerate/cool the engine down, all have different sizes, heights and rubber compounds, some are harder than others. The bigger the engine, the bigger the impeller. All rotate clockwise as the engine does, are located in the upper tail section inside a eliptical pump case, which is covered on top by a housing assembly, are moved by the drive shaft that moves the propeller and comes straight down from the piston crank shaft. Their delivering water pressure will depend on the engine rpm, lower-less, faster-more.
To replace when water pressure is low or as a peace of mind, once the leg is down, remove housing, place new impeller down through the drive shaft (put key to lock to shaft) until seats on top of the guide plate, oil, grease, soppy water the circunference of the pump case and impeller rubber blades. While pushing down the housing, keep turning the drive shaft clockwise untill the impeller is aligned inside the housing and well seated against plate, torque tight fastening screws to manufacturer specs. Grease impeller housing to avoid salt formations and whole drive shaft with a generous amount specially on cuts top shaft (where engine crank & shaft meets) to prevent seizing up with time. Try wheel bearing Lubrimatic marine salt water resistant grease if possible to get, has a trade secret long lasting formula.
If you are a peace of mind impeller changer, keep the old ones at hand, if your impeller has a straight border to border cut you can reverse them in a low pressure/out of stock emergency. Simply flip the impeller, grease and rotate it clowcksie untill corrected seated. Do so, only if the rubber blades are in perfect pumping condition, that is not heavily bent, nor rubber cracked. Will increase the water pressure, and last long. Check that all seal rubber water pipe connectors are ok, replace if necessary.
If not changing the pump case, a good suggestion would be to polish the internal cylinder, water moisten a used 3M green pad (the waffer type) and apply a generous amount of tooth paste, gently polish in both circle directions with finger untill the wall feels soft and even. This will make the new/reversed top blades of impeller last longer and pump better top pressure.
The photos will give a better visual idea of the related impeller issues & procedures treated on this review.