Overheat alarm - 1975 Johnson 50 hp(***Video added***)

[Hrokor]

Recently got engine running and put in the water, 50 yards out the overheat alarm sounded. Engine definately too hot. Replaced grungy thermostat/pressure valve. Rebuilt water pump/impeller. turned over on muffs in driveway and it appears to be the same. No water coming from exhaust holes in back and seems to be heating up pretty quickly. When LU was removed I blew through water tube and appeared to be clear. Any ideas?

 

[Solittle]

Re: Overheat alarm - 1975 Johnson 50 hp

Re: Overheat alarm - 1975 Johnson 50 hp

It is normal for water not to flow from the exhaust ports when running on the muffs at low rpm. Test again with the boat in the water.

 

[Hrokor]

Re: Overheat alarm - 1975 Johnson 50 hp

Re: Overheat alarm - 1975 Johnson 50 hp

Adding video:

 

[Haffiman]

Re: Overheat alarm - 1975 Johnson 50 hp

Re: Overheat alarm - 1975 Johnson 50 hp

Water level too low in the bucket, increase about 10" min. Seems to be a lot of leakage from the pump?

 

[BonairII]

Re: Overheat alarm - 1975 Johnson 50 hp

Re: Overheat alarm - 1975 Johnson 50 hp

Water level too low in the bucket, increase about 10" min. Seems to be a lot of leakage from the pump?

Water is def low. Need to be over the inlet screen. Is it possible that the OP's plumbing (in the leg) is disconnected?

 

[JDusza]

Re: Overheat alarm - 1975 Johnson 50 hp

Re: Overheat alarm - 1975 Johnson 50 hp

Definitely missed the water pipe hook-up coming out of the pump and going up to the block. Whatever water is getting picked up, and the water level is far, far too low, is just getting thrown into the case, not through any plumbing.

How are the seals at the ends of the water pipe, are they in place; one on top of the water pump (bottom of the water pipe) and one at the bottom of the block (top of the water pipe)? If they are bad, or not seated properly, a good pipe hook-up can still barf.

But, if I read you right, you changed the water pump impeller after the alarm went off. So, this water works display is after you changed the impeller. I would suspect you missed the water pipe. But, then, we haven't answered the original failure mode yet, have we? Gotta stay focused.

I suggest you get the unit into deeper water. Open the engine cover and disconnect the water outlet tell tale at the block. Blow compressed air backwards into the block. The air should travel the cooling water path , just in the opposite direction. You should see air bubbles coming out of the water intakes in the barrel of water. If not, the path is blocked; not sure where yet, but you know it is blocked and that's where the original problem comes from.

What was the history of the engine before this trial? Was it ever running, pumping water while in your ownership?

Be glad the alarm went off.
J

 

[Hrokor]

Re: Overheat alarm - 1975 Johnson 50 hp

Re: Overheat alarm - 1975 Johnson 50 hp

Water is def low. Need to be over the inlet screen. Is it possible that the OP's plumbing (in the leg) is disconnected?

Ok, I thought the water had to just be above where the muffs attach, I will have to check the upper seal. The seal on the water pump that goes over the water tube is good and attached.

 

[Hrokor]

Re: Overheat alarm - 1975 Johnson 50 hp

Re: Overheat alarm - 1975 Johnson 50 hp

Definitely missed the water pipe hook-up coming out of the pump and going up to the block. Whatever water is getting picked up, and the water level is far, far too low, is just getting thrown into the case, not through any plumbing.

How are the seals at the ends of the water pipe, are they in place; one on top of the water pump (bottom of the water pipe) and one at the bottom of the block (top of the water pipe)? If they are bad, or not seated properly, a good pipe hook-up can still barf.

But, if I read you right, you changed the water pump impeller after the alarm went off. So, this water works display is after you changed the impeller. I would suspect you missed the water pipe. But, then, we haven't answered the original failure mode yet, have we? Gotta stay focused.

I suggest you get the unit into deeper water. Open the engine cover and disconnect the water outlet tell tale at the block. Blow compressed air backwards into the block. The air should travel the cooling water path , just in the opposite direction. You should see air bubbles coming out of the water intakes in the barrel of water. If not, the path is blocked; not sure where yet, but you know it is blocked and that's where the original problem comes from.

What was the history of the engine before this trial? Was it ever running, pumping water while in your ownership?

Be glad the alarm went off.
J

.
Pardon my ignorance, jdusza, but I was told that there is no tell tale on this motor. What exactly would I disconnect to blow air through? The history of motor is unknown. Because when I got it the former owner said all was well but it has always run too hot since I have had it. I have only taken her through a harbor, never opened her up.

 

[Haffiman]

Re: Overheat alarm - 1975 Johnson 50 hp

Re: Overheat alarm - 1975 Johnson 50 hp

The excessive leakage might be partly caused by restriction in the upper water tube grommet, which is quite a pain to change. Power head off and exhaust collector must off.
Pull down the gear case and attach a water hose straight to the tube, apply pressure (less than 20 PSI) and start the engine and let run at idle.
Check temp.
If hot, off with PH and exhaust collector.