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Johnson overheat alarm

N

N Wright

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"Ok heres the deal. Bought a

"Ok heres the deal. Bought a boat from a friend. It is in real good shape, and the motor runs real strong. It is a 93 johnson 40 hp. I have had it out maybe ten times, and the last time the overheat alarm came on. Constant alarm. I managed to get it back to bank, and took it to the shop. They said it was clogged up with trash, and cleaned it all out, and said there should not be any more problems, and everything else was ok. Too the boat out the same day I got it back, and after a few minutes of full throttle, the alarm went off again. needless to say I WAS Pi**ed. I called the mechanic, and he said my water pump may be weak. I checked the heads when the alarm went off and they were warm but not really hot hot. Pee hole has a strong stream, and otherwise the motor runs fine. Any ideas? I do not feel I should be charged another dime, because they said it was only trash in the line, and it was supposedly fixed. Opinions and ideas appreciated."
 
they should have repl the wtr

they should have repl the wtr imp the first time....where did they clean the 'trash' from?
 
Does the exhaust water get hot

Does the exhaust water get hot enough that you cannot hold your hand in it comfortably?it will be hot but you should be able to leave your hand in it..does the alarm go off at 3000 rpm?i would replace the water pump and check the compression..after that i would suspect a bad sensor..that vintage johnson had had sensor failures....btw:that pee hole is almost useless on a evinrude/johnson...it pees before the water goes thru the jacket...
 
"all i know is he said he took

"all i know is he said he took the thermostat off removed the guts and cleaned the trash out . The guy is a good mechanic, but i feel he should not charge me to fix it now. The water coming from the pee hole is cool, the head gets warm but not just unbearably hot. I can hold my hand on it for a count of 5. It still runs fine. Is there any way to tell you have a bad impeller? The stream is strong. Where is the thermostat on this motor?"
 
"That engine must have the the

"That engine must have the thermostat installed in order to function properly. If he removed the thermostat, the engine will run too cold, if it pumps at all, and will cause piston scoring.

Some people remove the thermostat in a false attempt to conteract a overheating problem BUT this simply adds to the problem as you've found out.

The water pump assembly (complete assembly) needs to be replaced along with a new thermostat and related parts.

The thermostat is usually located under the plate that is attached to the cylinder head."
 
Ok this motor is drivin me nut

Ok this motor is drivin me nuts. It runs like a top and the alarm has not come back on yet. I still dont get why the alarm went off on two seperate occasions. I ran it yesterday idle with muffs for well long enough to over heat. I felt the heads and they were hot to the touch. Could hold my hand on them for maybe 3 seconds. I have no way of checking temp on surface. Guy told me it should be 140 f. Like warm bath water. The thermostat sets right at the top of the head correct? Behind a cover with a hex head in the center of it correct. I took it off and turned the motor on. Water rushed out so I know Im getting circulation. Any ideas. How hard is it to replace a impeller on the 93 40? Never done it but I know how to use a wrench.
 
On the back, top of my Johnson motor there are 2 threaded holes to install a sensor. I use a small, pointed meat thermometer. On my boat it registers 165 degrees - which is close to the thermostat opening temperature. I too am having the hot water alarm going off.
 
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