Pre-1950 OMC Cooling System Question

[50's OMC]

We recently bought a 1929 Johnson 3hp (A-45) and we have a 1941 Johnson 9.8hp (KSL-15) and we can't figure out how the cooling system works. We know that they are not air cooled and we also know that their is a brass impeller instaed of a rubber one. But we can't figure out where the water comes out. On most newer motors(1950-now) their are holes in the motor body for water to come out so you know that the engine block is being cooled but all we found on these motors were holes for exhaust. So how do you now that these older motors are getting water to the engine block and not overheating?

 

[1946Zephyr]

Re: Pre-1950 OMC Cooling System Question

Well, I'm not sure about your 1941 Johnson, but I did own a 29 Johnson once. Those are basically a ram force fed type I guess you could call it. There is a inlet behind the prop where the water is picked up. The force of the prop, or the movement of the boat will make the water go up that inlet and force the water up into the powerhead. Some of the earlier "waterbugs" had a piston type pump, but a lot of old Johnsons were built without water pumps all together. As I recall, the SD models didn't have water pumps either.

Just make sure the passages are good and clear of any blockages

 

[F_R]

Re: Pre-1950 OMC Cooling System Question

We recently bought a 1929 Johnson 3hp (A-45) and we have a 1941 Johnson 9.8hp (KSL-15) and we can't figure out how the cooling system works. We know that they are not air cooled and we also know that their is a brass impeller instaed of a rubber one. But we can't figure out where the water comes out. On most newer motors(1950-now) their are holes in the motor body for water to come out so you know that the engine block is being cooled but all we found on these motors were holes for exhaust. So how do you now that these older motors are getting water to the engine block and not overheating?

Johnson used some strange cooling systems down through the years. I'm old but not old enough to have the answer. But there are guys over at the Antique Outboard Club that can answer your question, and they aren't even all that old. Go to the Ask-A-Member forum at www.aomci.org

 

[cougar1985]

Re: Pre-1950 OMC Cooling System Question

Ok,im reading out of the 1939 22.5 hp evinrude speeditwin manual as i type.The pump is know as a single stage centrifugal type.Due to the simplicity of the design ,the wearing of moving parts is entirely elimimated.The 39 speeditwin runs with a automatic exhaust relief.While the motor is being started,the exhaust relief automatically provides a bypass from which ehaust pressure instantly escapes into the air,unchecked by water seal.As quickly as the motor attains normal revs,the relief is automatically closed by a flow of circulating water,and the noise and fumes diverted to the water sealed exhaust outlet.At slow speed therefore,the water will emit in a spray forced out by exhaust gases.At higher speeds water flows in solid stream from discharge in muffler.

 

[F_R]

Re: Pre-1950 OMC Cooling System Question

Ok,im reading out of the 1939 22.5 hp evinrude speeditwin manual as i type.The pump is know as a single stage centrifugal type.Due to the simplicity of the design ,the wearing of moving parts is entirely elimimated.The 39 speeditwin runs with a automatic exhaust relief.While the motor is being started,the exhaust relief automatically provides a bypass from which ehaust pressure instantly escapes into the air,unchecked by water seal.As quickly as the motor attains normal revs,the relief is automatically closed by a flow of circulating water,and the noise and fumes diverted to the water sealed exhaust outlet.At slow speed therefore,the water will emit in a spray forced out by exhaust gases.At higher speeds water flows in solid stream from discharge in muffler.

That is interesting and informative, but completely unrelated to the Johnson motors in question. I have the water pump repair instructions for a A-25 but have no clue whether or not the A-45 is the same. The A-25 is a plunger pump.

 

[cougar1985]

Re: Pre-1950 OMC Cooling System Question

Of course your correct fr.I should of added that i was merly pointing out about the water circulation more so than the type of water pump employed.A lot of the older motors employed this system but maybe not all.

 

[1946Zephyr]

Re: Pre-1950 OMC Cooling System Question

That is interesting and informative, but completely unrelated to the Johnson motors in question. I have the water pump repair instructions for a A-25 but have no clue whether or not the A-45 is the same. The A-25 is a plunger pump.

Yea, I had an A-45 F_R. They actually did away with the waterpumps in the 29's The motor I had basically just had a system that was like a tunnel ram type system that had the pick up inlet right behind the prop. As the motor is running and the boat is moving, the water was forced up this inlet and up to the powerhead. No moving parts at all.

Mine didn't work very well. I may have had a clog, but I spent a whopping $2.00 on the motor to get it to run (after it was given to me) and it ran like a champ. I could grab the flywheel with my hand and give it a quick twist and she would fire up. Not bad for a motor that was almost 70 years old, at the time I had it.

The following year, (1930) the A-50 model was an alternate firing twin and had the inline two cylinder configuration. I had one of those too, as a matter of fact. It was a nice runner, but again, the same kind of cooling system and it didn't work all that great. Mine did have a soft plug out, but I think it did have water coming up to it.

 

[TN-25]

Re: Pre-1950 OMC Cooling System Question

Johnson referred to those old style cooling systems without any moving parts as "pressure vacuum" cooling systems. Since no outboards had neutral or a reverse prior to the 1949 Johnson 10 (Scott-Atwater came out with the F-N-R shift for '49 as well), any time a motor was running it was also spinning the prop. The spinning prop would obviously have lots of water pressure behind it, so a little scoop placed behind the prop (by the exhaust outlet) would have water forced up and into the block. Water returning from the block would go out through slots in the prop (this is way before the through-hub exhaust). Water leaving the motor via the slots in the prop would also be "pulled" via the low pressure in the slip stream around the prop cone, Thusly the pressure-vacuum cooling system got it's name. Water is forced up the pickup from the prop wash and is eventually drawn out via vacuum around the prop cone. The old SD motors (16 hp 1940-50) used the pressure-vacuum system, as did the long running KO 22 horse opposed twin (decended from a 1929 design built through 1950) and likely most of the older Johnsons.

Some motors used a simple rotor on the prop shaft (MS-MD-HS-HD-TS-TD & predecessors). Once the shiftable lower unit was invented they had to invent another means of moving water into and out of the block (remember, in neutral the prop doesn't turn, so a water pump that relies on the prop turning won't work). Enter the flexible rubber vaned impeller. They reside below the water line around where the mid-section & lower unit join. Even when the lower unit is in neutral or reverse, the drive shaft is still turning in a fixed direction whenever the motor is running. It therefore is what the impeller-type water pump is driven off of. The TN 5-horse (1950-53) differed from the TD/TS (1941-49) in that the TN used this new impeller.

 

[wilde1j]

Re: Pre-1950 OMC Cooling System Question

Why not get a shop manual for your motor instead of getting WAGS?

www.outboardbooks.com

 

[50's OMC]

Re: Pre-1950 OMC Cooling System Question

Good idea but what are WAGS ??