1962 Johnson RKL24 40 hp. Doesn't overhear but no water out exhaust discharge

Hoping someone has run into this before. Installed new impeller and confirmed that water is flowing through the system properly except little to nothing through the discharge only exhaust. Ran the motor for over 15 minutes in a test tank and never got hot. I have removed the powerhead looking for obstructions and both welch plugs on the cylinder head. The only reason I haven't removed the large welch plug on the upper exhaust housing is because I don't have that size and I am not sure there could be a blockage that would cause this problem there anyway. Any thoughts?

Is there water spitting out the exhaust relief ?-----------Most of the cooling water goes out below the water line !

I have replaced the thermostat and even ran it briefly without the thermostat to test water flow. All without noticeable change. But, on a couple of test runs I did have a sort of gush of water and steam after about 2 minutes and then back to nothing. Yesterday I ran it for about 3 minutes and it did have a very small amount of water coming out of the discharge. Then I started it again and ran it for about 16 minutes with no water at all coming from the exhaust relief / discharge outlet. I could hold my hand on the head, thermostat cover and exhaust cover the entire time. I like the Saltaway idea. I have never used it. I am still thinking that the welch plug (item 10, p/n 307541 on the parts list) may be blocked but I hate to pull it if it is worthless. I know that there are 5 or 6 small holes behind it which apparently receive water from the outlet side of the cylinder head water jacket but I can't tell if a blockage there would effect the discharge. All of your insights and thoughts are appreciated. Thanks.

You need to pause and think about how that system works. It is a thermostat-controlled recirculating cooling system. When you start the motor, the water goes up and circulates through the powerhead. Then it is presented to the thermostat. If it is not warm enough, the water is directed through that plastic check valve and goes back down to the water pump for recirculation. Back up for a repeat of the first trip, and if still not warm enough, back to the water pump. This can go on all day if the lake water is cool and the motor is not developing a lot of heat (slow speed, and a good water pump).

Now, even while in recirculating mode, a bit of water is discharged. This is necessary to cool the exhaust (and that electric shift cable). Also, a bit will spritz out the above water exhaust relief as a tell tale. Because some is being discharged at all times, new lake water has to be added to make up for it. THAT is why it can run so long with the 'stat remaining closed.

When you run at higher speeds and/or loads, the powerhead will get warm enough to open the 'stat. That is what happened when you briefly saw a heavier flow, normal for a warmed-up motor. BUT. remember, it is not a thing of the 'stat being either open or closed. It is constantly sampling the water temp and opening and closing as necessary to maintain the proper temp.

I typed all this simply to tell you that there is nothing wrong with your motor. As long as it is not overheating, as you indicated, it is acting normally, as designed. So don't "fix" it.

When you are skiing behind this motor you will see water pouring out that idle relief hole.---------Then when the motor is idling and picking you up you will see lots of water and vapour coming out that hole ( it is not steam ).----Then as motor temperature stabilizes you will see it spitting out a bit of water again.

fdrgator said:

You need to pause and think about how that system works. It is a thermostat-controlled recirculating cooling system. When you start the motor, the water goes up and circulates through the powerhead. Then it is presented to the thermostat. If it is not warm enough, the water is directed through that plastic check valve and goes back down to the water pump for recirculation. Back up for a repeat of the first trip, and if still not warm enough, back to the water pump. This can go on all day if the lake water is cool and the motor is not developing a lot of heat (slow speed, and a good water pump).

Now, even while in recirculating mode, a bit of water is discharged. This is necessary to cool the exhaust (and that electric shift cable). Also, a bit will spritz out the above water exhaust relief as a tell tale. Because some is being discharged at all times, new lake water has to be added to make up for it. THAT is why it can run so long with the 'stat remaining closed.

When you run at higher speeds and/or loads, the powerhead will get warm enough to open the 'stat. That is what happened when you briefly saw a heavier flow, normal for a warmed-up motor. BUT. remember, it is not a thing of the 'stat being either open or closed. It is constantly sampling the water temp and opening and closing as necessary to maintain the proper temp.

I typed all this simply to tell you that there is nothing wrong with your motor. As long as it is not overheating, as you indicated, it is acting normally, as designed. So don't "fix" it.

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Thanks for the thoughts. I wasn't thinking about the recirc making a difference. What confuses me though is that I have worked on the water pumps & gearcases of similar models with the recirc' and there is always plenty of water flow out of the relief. I was just sure that there had to be a blockage somewhere. With that in mind and thinking about how this system works, if I run it at higher idle, say 2000rpm and there is no blockage, I should be able to recreate the water gush that I mentioned earlier. fdrgator, anyone else, do you agree? By the way this is running in a 100 gal tank with the lower unit submerged up to midway on the 5" extension, to answer a couple of other questions.

Depends entirely on the temperature at the thermostat.

There is something I didn't mention. Above the pleated relief hose is a core plug. Behind that plug are about 4 holes that the water goes through on the way out. It's been a long time since I've studied that area, but I do remember it affects the amount of visible discharge if trash accumulates in them. You might want to take a looksee if you are still concerned.

fdrgator said:

Depends entirely on the temperature at the thermostat.

There is something I didn't mention. Above the pleated relief hose is a core plug. Behind that plug are about 4 holes that the water goes through on the way out. It's been a long time since I've studied that area, but I do remember it affects the amount of visible discharge if trash accumulates in them. You might want to take a looksee if you are still concerned.

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Yes, this is the plug that I mentioned in my original post. I was hoping that someone was more familiar with it than I am. So it sounds like it would be worth removing the plug to inspect. Thanks. I will pull it tomorrow and tell you what I find.

So just a brief update. I pulled the welch plug mentioned in the previous response. I found only a little water. Nothing blocking the holes that I could see. I blew compressed air into the holes but couldn't tell if I did anything. Now I'm waiting for a replacement plug. I'm thinking of running it without the plug to get a better understanding of how the water flow works in that area. I'll keep you posted.

Cascade Classic Outboards said:

So just a brief update. I pulled the welch plug mentioned in the previous response. I found only a little water. Nothing blocking the holes that I could see. I blew compressed air into the holes but couldn't tell if I did anything. Now I'm waiting for a replacement plug. I'm thinking of running it without the plug to get a better understanding of how the water flow works in that area. I'll keep you posted.

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Another update: Ran the motor without the welch plug and saw no difference. Other than a little water spitting from those holes. Got the replacement plug installed and planning to run salt terminator through it.
Anyone know if you can flush effectively by mixing in the test tank or do you have to use the mixer?

I will check it. I did blow the screen out and it looked OK, but I will pull it to be sure. Thanks for the thought.

The screen was fine, I used the Salt Terminator with the mixing unit (tried to make my own first, didn't work). Not sure if it helped, but I am sure that it didn't hurt. Now I have to replace another generator belt (already bought one and it broke) Wondering if a belt from a Honda 8 or 9.9 would work, but I will start a new thread. Thanks for all of the help!