Johnson 3hp (1960s): Check cooling water circulation

[davedublin]

Hi guys – I'm working on a nice little Johnson 3hp from the mid-1960s. I want to check if water is circulating as it should. I'm puzzled about the cooling water outflow. I've had the underwater assembly off the power head and confirmed that the copper pipe from the water pump is seated in its groove with the locating rubber underneath the power head. I looked at the impeller and it seems OK, and the pipe is a tight fit in the seal at the top of the impeller housing. The key in the prop shaft locates in the slot in the centre of the impeller.

I looked for water exiting the many small holes in the underwater unit, but there is no water, only exhaust. Does cooling water exit anywhere else, e.g. via the two holes just above the anti-cavitation plate? If no water exits the many small holes half way down the underwater unit, does this mean a water pump strip-down once again and any further investigation?

I've included some pics of the exit holes in the underwater unit and the water delivery pipe mounting on the underside of the power head. The first pic shows the multiple small holes where exhaust exits the u/w unit. The second shows the two small holes above the anti-cavitation plate.

I'd appreciate your advice on how to ensure that the water pump is working and that water is circulating properly on this motor.

Dave

 

[Spartans]

At a minimum with those itty bitty motors you should get a mist From those holes Does the impeller pump water with the lower end off ?

 

[F_R]

The water blows droplets out the holes in picture #1, but only by chance. As for the ones down below, you can't even see those if the motor is deep enough in the water, so why are you asking?

 

[davedublin]

Thanks for the replies. So now I know one shouldn't expect a spray of water from those multiple holes.

Spatans: I will try testing if it pumps water with the lower end off. Good idea, I hadn't thought of that!

F-R: I am familiar with the larger Johnsons of the period, in which you can see a clear flow of water from the u/w unit when the pump is working properly, and that is reassuring. I'm asking because I am unfamiliar with these models and just want to know where the water that has circulated around the water jacket eventually exits. I don't want the thing to seize. It belongs to a friend and it was his Dad's so it's valuable to him.

 

[F_R]

Most of it exits with the underwater exhaust, behind the prop.

 

[racerone]

Facts for you.----Most small motor do NOT have an overheat warning / shut down system.----They will run till they seize up.-----A prudent owner would install a new impeller now.----And every 5 years after that !!

 

[davedublin]

F-R: good to know, thank you. I ran the motor in the barrel and checked the block with a hand from time to time, and my judgement is that it was running cool.
racer one: Thank you. A new impeller is already on its way!

 

[backwater52]

good idea installing new impeller, you can test the them with a battery drill on the shaft. but that don't mean there is no blockage in the water passages in engine.

 

[oldboat1]

Look underneath the powerhead on the left rear side of the motor. There may (or may not) be a screw on your model resembling a vent or fill screw on the lower unit. If the screw is present, loosen it with a large bladed screwdriver, and then briefly remove it with the motor running. If the pump is working, there should be a strong stream from the opening.