1977 Johnson 115 overheating after new water pump

[Newboatowner]

My '77 Johnson 115 was running too hot so I changed out the impeller. Took it out to the lake and ran it for about 7 hours with no problems at all. The following weekend I took it back out and after about 3-5 minutes of nearly WOT my alarm went off. I let her cool down then began to head back to the dock. With my wife steering the boat, I went back to check the water flow and it was flowing out the back of the motor pretty good, put my hand in the stream and it was pretty warm water. Shortly before I reached the dock the alarm went off again. If I got good water flow up to the heads and the warm water coming out tells me it's flowing through the heads and out....then why am I still overheating??

[Greg Moss]

The rubber water deflectors in the cylinder water passages might be swollen up and blocking some of the water flow in the block. or the T-stats might be stuck on one side. If you had your hand in the pisser then it might not be giving you a real indication of the water temp. Pull the cowl and see if there is a difference in the temp of the 2 heads and also see if you can feel the water temp coming out of the 2 exhaust relief holes.

[mfm]

Everytime that happens to me it is the thermostats. Water will still flow out of the pisser and the exhaust relief ports even when the stats are shot. For $24 and some frustration [ the springs in the thermostat block ] you will be good to go.

[Newboatowner]

Thanks fellers, I appreciate you help.

[flabum1017]

Warm water out of the pisser, the water there should not be very warm since it is near where the water comes into the motor. I'd say deflectors as well.

[Newboatowner]

I'm a little confused now. What ya'll are calling the "pisser" is that on the lower unit? Where I checked was the 2 holes just below the cowling, I'm assuming this is what Greg Moss called the "2 exhaust relief holes"? I noticed water squirting out of the lower unit toward my transom looked to be about the same size of stream as....well....peeing. I could'nt bend that far down and check the temp there.. I do however have lower unit oil leaking out of that same hole.

[flabum1017]

I see you have a 1977 motor.... my bad....you don't have a pisser.


A pisser is a small hose attached to a small fitting in the engine pan that pisses water out to let you know your'e pumping water. Your motor is too old to have one.