By author Trish Dougherty
Obtain a Seloc or stern drive service manual and read the section on OMC engine water pump and cooling system.
Place the boat in the lake not a pail of water or garden house with rabbit ears being
placed on lower water pick area. This work great for outboards and Mercruiser lower units but not for 400-800 series lower
unit do to the fact that unit is located in the upper gear case.
Install a radiator flush kit between the water pick
tube up from the intermediate housing and the thermostat housing and check water flow. there should be a steady flow of water
at 550 to 600 rpm. water should not have large amount of bubbles as water flow out of it.
If steady water flow is about
1-1/2 to 2 gallon per minute to fill pail then you need to check each manifold.
120 pounds of back pressure from the
engine manifold leaking exhaust gas into the cooling area can stop or slow down the impeller from pumping. Low rpm will often cool engine
and high rpm will not. Impeller can be damage from large exhaust gas leaks in minutes. This problem often come to life after
the winter season layover.
Water flow area on the exhaust manifold should be clean every 400 hours or 5 years
to run the boat for short times say 5 to 10 minutes, you can run the garden hose into a radiator flush kit to cool engine
and this will run water into impeller housing as well.