Johnson RDS-20 water tube confusion

[Robert p GOODWIN]

I always install a new impeller on any engine I pickup but I am having problems with this one. The IPL shows two copper water tubes of the same length going into grommets on top of the pump housing.but I have one long one and one short one. There are two grommets on top of the pump housing and one well down into the lower unit. The long tube is self explanatory but I am at a loss as to the top ones

 

[F_R]

The lower unit has been replaced with a 1968-69 unit, not sure which. But I think 1969. The water tubes underwent a couple of design changes about that time. I think if you examine the cap on the pump housing, one of the tube grommet holes is blocked off. The tube that used to go into that side now goes down into the intake area in the bottom of the case. That is the warm-water recirculation tube returning to the pump intake. Used to go into the pump, now into the intake in the gearcase. Serves the same function.

Anyhoo, the second, blocked hole in the pump cap still has the grommet hole, but doesn't need a grommet in it because it does nothing.

 

[Robert p GOODWIN]

AWESOME!!! Just not real happy with the temp and not seeing much coming out the back end. Much prefer the tattle tales. So the warm water exits below the water line?

 

[jimmbo]

It doesn't exit, it is returned to a place just downstream of where new water is picked up and returned to the pump. Might have been a way to lower the temp of the water in the pump as the recirculating water would be diluted by cooler new water.
The 58 - 68 V4s always directed the recirculated water that way

 

[F_R]

When the thermostat is closed, water returns to the pump for recirculation. That continues till it is warm enough, then 'stat opens, water is discharged and replaced with cool lake water. This is going on constantly, with 'stat opening and closing as necessary to maintain proper temp. Think about it, that is almost exactly how your car works, except a radiator is used for cool water instead of a lake. Only difference is the outboard discharges a bit of water to cool the exhaust.

 

[Robert p GOODWIN]

Thanks so much for clearing that up. Didn't even think about a stat on this motor. Another PM item. I have one on order .
Is there a way to add a tattle tale on this unit or another way to ensure the pump is up to snuff? OR....is there another pump housing that will work that isn't a couple hundred bucks?

 

[racerone]

In my opinion a tell tale is not needed if you maintain the cooling system.----Brother owned a 1965 Evinrude for some time and we never worried about a tell tale.

 

[F_R]

Same here, I've owned a lot of motors over the last 60 years, and except for my present one, none had a squirt hole. But nowadays, it seems everybody enjoys watching something pee.

 

[Robert p GOODWIN]

While I can certainly respect your opinions.....may you never be "blessed" with a Son In Law who doesn't know what muck does to water inlet holes or sand and pebbles do to an impeller. So today, I was sure this motor was getting hot because of a sticking stat. Pulled the housing and there isn't one in there....

 

[jimmbo]

If you SIL operates your boat with such Disdain, why do you let him? If it his boat, then a few big repair bills might be the Attitude Adjustment he needs

 

[Robert p GOODWIN]

Because he treats my Daughter well and as a financial planner....he can afford the repair bills. I'm well past the age where I can be grateful for some things and overlook others.

 

[Robert p GOODWIN]

So...in reading another thread on T-stats...some engines require one in order to fill the water jacket. I could see where the water might flow down and out without picking up the heat. I did drop the lower end in a can of water and turn the shaft fast enough to ensure the pump was working. Just occurred to me that I can reassemble the lower end and spin the motor with the T-stat cover removed to check for pump operation.

 

[F_R]

Don't fool yourself. Spinning the shaft without actually running the motor does not provide exhaust back pressure. Exhaust leaking into the pump kills the prime.

So, there was no t'stat huh? How about the plastic thermostat housing and check valve? Lack of a thermostat by itself won't make it run hot. But leaving the housing and check valve out will.

 

[Robert p GOODWIN]

Check valve is there. Granted... while I am a moderator on PPETEN (a small engine forum)...outboards older than I am is not my natural forte.So I am not fooling myself about anything.....I'm asking you ....

 

[F_R]

PPETEN eh? I'll have to check that out. I cut my teeth on old Briggs, Clintons, etc.

 

[Robert p GOODWIN]

Not sure what I did but water now comes out the exhaust relief!!!