Reply To: 1953 Johnson Seahorse 25 hp RD-15 not pumping water

[fisherman6]

I think the confusion here is that the RD-17 has the later design water pump where the water tube plugs directly into the pump housing. I have not had an RD-17 apart but I have had a ’54 Big Twin and a couple of RD-16s apart and they do have a water channel in the area between the midsection and the gearcase. On these earlier ones, the seam between the two halves actually forms a channel into which the water pump discharges water. The water tube carries water from this channel up to the powerhead. It makes the gearcase easier to line up only having the shift rod and the drive shaft to be concerned with. It also means that the seam between the two halves must be pretty well sealed. There is supposed to be a gasket between the two halves to seal this cavity up. I have used a gasket in one of the three that I have worked on and the other two I used Yamabond on the joint at installation because I didnt have a gasket and didn’t feel like making one. I tried it once and it worked great so I did it again on the next one. If yours has a water tube that is not connected to the channel, that is likely the problem. So far I have not had one with the tube disconnected from the channel. If it is, it will just pump water into the exhaust housing and out into the lake without the cooling water reaching the powerhead. I do not remember if the water tube is fitted into a grommet in the midsection above the channel or if it is just flared at the bottom. I seem to remember being able to see the bottom edge of the water tube in the top of the water channel though. Someone else can probably fill in the gaps here.
-Ben

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