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71 Johnson 50hp hydro elective drive.

H

Heavymetal2000

New member
So I just recently got my 50hp outboard going. It's a 71 50hp Johnson hydro electric drive.
I brought the boat down to the launch afterwards to check for water flow from the pump and noticed there is no usual water line to discharge water.

It does have a spot on the rear side under the engine bay that says water shield silencing and it has two vertical slots.
After the motor ran for a minute or so I had water coming from both slots.

Is this normal? Is that cooling water as well or am I missing something?

I did some googling, but you'd be surprised how few results you get regarding the water silencing and this particular motor.

Thanks for any help, I just dont wanna take her out if she's not cooling properly.
 
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(Exhaust Relief Ports - Exhaust Housing (Inner/Outer)
(J Reeves)

The long housing between the powerhead and the lower unit is called the exhaust housing. There is a inner housing within it that has a heavy duty seal around the bottom of it, or heavy duty seals around a inner extension between the housing and the lower unit.

The red hot exhaust travels down thru that inner tube and out the propeller with a somewhat supply of water to cool the propeller hub. A good amount of water surrounds and fills the space between the outer and inner tube, otherwise the outer housing would get so hot that the paint would burn off.

Some water pumps, for some reason (differing even when new) exert a great amount of water pressure, and if the exhaust housing seals are in perfect condition, the water fills the tube to a point of overflowing.

This brings into play those two holes or slots, whichever the engine might have, at the top rear portion of the exhaust housing just below the powerhead.

Now, if those two holes/slots weren't there, water would continue to flow up into the cylinders. Water not flowing out of those holes is no concern for alarm UNLESS that outer housing suddenly becomes extremely hot..... the warning horn should sound long before that happens.

The main reason for those holes being there (exhaust relief holes) is that when at an idle, there is an extreme amount of resistance encountered by the exhaust trying to escape due the fact that the outlet via the propeller is now blocked by a wall of water. The escape route in this case is for the exhaust to escape out those two holes, otherwise the engine would slow down quite quickly and die. If exhaust cannot escape, air/fuel cannot gain entrance to the engine.

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In other words, it is normal for water to spray out those exhaust relief holes. That is your "tell-tale" so to speak.
 
Definitely appreciate the detailed explanation, I did have exhaust exiting those two slots upon initial start up, then it started spewing water. Which is apparently normal, and good.

As for cooling? Is there no water exhaust line further up at the power head like my other outboard? I have a Johnson 8hp as well and it spews water from below the power head back into the water when running.

Also, any link to this horn/light for overheating? Just to be sure I have it hooked up and it's working. It's been sitting for 3 years.

I'm doing the foot oil and changing the plugs just to freshen her up. And i hooked it up to a tank of fresh 91 pre mixed at 50:1 with semi synthetic smokeless ashless oil.

Is there anything else I should consider doing prior to taking it on a good run?

It's currently on my 16 foot tri hull.
 
No "Pee Hole", as often called, on your '71 motor. You don't really need one unless you just like to see something pee.

There is a temp sensor in the cylinder head with a tan wire going to it. Turn the key on and ground the tan wire. Horn should blow.
 
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