Reply To: 1961 Johnson 40 (RDSL-23) stops pumping water

[Don]

OK, well I too, am very concerned about the condition of that gearcase…It is badly eroded/corroded from salt or some other electrolysis issue…There may be an issue with the casting underneath the water pump that connects the pick up to the area under the pump….Creating an air leak…This area is full of water when you first start it, explaining why you see water flow for a few seconds…Once started some of the water down there is displaced by exhaust pressure, which may be sneaking its way into the water intake path….I’m not referring to the mating surface between the SS impeller plate and gearcase housing, I am referring to the cast in water passage leading up from the water pick ups. You have tried a new impeller, then reinstalled the old one just in case the new one was NG. Same results with both. You mention the aluminum impeller housing looks “OK”, and you have replaced the seal. There is a tiny vent hole in there that could be plugged though, which could explain this…Sorry, don’t have a picture, perhaps someone else can post one.
OK, seems like you realize that you can’t judge cooling operation from the upper exhaust discharge very well…You should see a continuous gurgling of water coming out of the thermostat pocket while running with the cap removed…Keep in mind that running with the cap removed might just cause most of the water to spill out all over which would explain why you don’t see much coming out of that choke water port…The thermostat housing is upstream of the cylinder jackets. Nonetheless, you have convinced me that the engine has a cooling issue…Water should not stop pouring out of that thermostat pocket with the cap removed running in neutral. Although running the engine in forward gear does help force water up and into the pump…So, a marginal pump could exhibit a condition where the engine pump fine in gear, but fades out in neutral like you describe…
OK, yes, it does look as though someone did replace the engine block, perhaps a powerhead…..But, the engine seemed to cool OK that last time you used it many years ago….But, since that time, mice made a home in there…Mice pee is very corrosive indeed. Was there a mouse nest inside the gearcase exhaust cavity when you removed it to do the water pump job?
And yes, you are correct, that little check valve spring is very light indeed, almost non existent. That check valve is there only to keep the cooling water from “short circuiting” out of the block without circulating through it first…So yes, there would be very little resistance on it. This is a relatively complex cooling system, which is why it has two water tubes….Cool water is meant to circulate back down through the pump to help heat up the water, warm up the engine….
Frank will correct me, or point out more areas to be inspected/checked….
The easiest test for what I suspect would be to install another known good gearcase…I realize this is something you don’t have laying around though….I sure hope I my suspicions are incorrect…D