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2004 15HP Johnson 2-stroke Cooling Problem

R

Robert1997

New member
Hey this is my first thread, im sorry for my bad english I'll try to make it as clear as possible what my problems are.

So I bought this Johnson 15HP motor from a guy which said everything was in perfect condition (not gonna lie it looked like it was in good condition when he sent videos of it) so I brought it back home - immediately went to test it out and upon testing I had some troubles with cooling when I started the motor. It did not want to cool it self at all on low rpms, only when I put it in foward gear and started going fast then the water started "peeing" from the tell tale. First guess for me was the thermostat did not open at the start (but I wated there in neutral for a couple of minutes before putting it in gear..) I brought it to my garage for further inspection and I found out that the impeller was burnt to hell.. the blades were melted I have never seen that before so I ordered a new pump kit and installed it then I went to test it again and for some reason there was no water coming out at all (not even in gear).

So I brought it back again to my garage to do a second fix - I opened up the cylinder head plate and the water plate on the side of the motor to clean all the water passage ways - after I opened it I was shocked how much salt there was built up around the passage ways :( So I cleaned it very thoroughly almost to bare metal for more efficient cooling and closed the plates back up with my own made gaskets (I live on the other side of the planet so ordering new gaskets from USA takes a while for it to come..) well those gaskets that I made my self were great! The water was running at low RPMs as it should do, it was not hot and the stream was really good and I tested it on the water and it ran really good up until I decided to invite some friends on my boat and I put some load on the motor... with 4 people on board it was pushing water hard until it suddenly completely stopped...

I got back to my garage again for more fixes and I couldn't figure out what was wrong - but I decided to take a month off of fishing and I ordered new parts from the USA. When they arrived I re-installed everything they sent me (gaskets, grommets, thermostat, water pump kit) cleaned all the passage ways again, and now I am struggling even more than before... The telltale is weak at low rpms (very very weak) to the point where I can't keep my hand on the flow because it burns.. in gear it decides to stop completely especially in reverse which is super weird :confused: I tested it on a lake and no difference there either :( I will attach a video link for you to see how it works now, maybe you'll have some ideas on how should I continue with fixing it or should I just let go and move on with my life. https://youtu.be/RpmwxSVb0rY
 
Have you looked the grommet at the top of the water tube ? #19 in the parts diagram

It's a pain on my 6hp because corrosion around the grommet squeezes ii over the top of the tube until it cuts off the water flow but the 15hp may not suffer from the same problem especially if it has always always been a lake motor rather than salt water

Big job to access because the power head has to be removed .

With the gearcase removed try connecting a water flow to the water tube. Take the thermostat out and leave the cover off to see if you get a good flow or not

Also if the grommet is the problem a stout wire pushed up the tube will hit it and it will feel rubbery .

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vics said:
Have you looked the grommet at the top of the water tube ? #19 in the parts diagram

It's a pain on my 6hp because corrosion around the grommet squeezes ii over the top of the tube until it cuts off the water flow but the 15hp may not suffer from the same problem especially if it has always always been a lake motor rather than salt water

Big job to access because the power head has to be removed .

With the gearcase removed try connecting a water flow to the water tube. Take the thermostat out and leave the cover off to see if you get a good flow or not

Also if the grommet is the problem a stout wire pushed up the tube will hit it and it will feel rubbery .

View attachment 29328
Click to expand...


it was a salt water motor before but now I cleaned it as much as I can and now its only been running on lakes. yes I replaced the grommet you mentioned (the #19 part) into new one but nothing changed but I'll try to do a test with gearcase removed to check the water flow.
 
alright ill see what I can come up with I'm gonna look for a new test bucket since that one is too short to supply it with enough water.. but I still don't get it how other people make it work even when water levels are below the water pump.. I've watched so many videos on YouTube about the same motor and some of them push more water than mine even when the water level is below the water pump. very strange. I will also try to connect directly to a water hose to supply water even more efficiently (but in my opinion you get innacurate reading of water flow since you get water pressure from the hose it self thats why I always choose a test bucket)
 
racerone said:
Water must be 6" ( 15 cm ) above the impeller in your test bucket.
Click to expand...

alright ill see what I can come up with I'm gonna look for a new test bucket since that one is too short to supply it with enough water.. but I still don't get it how other people make it work even when water levels are below the water pump.. I've watched so many videos on YouTube about the same motor and some of them push more water than mine even when the water level is below the water pump. very strange. I will also try to connect directly to a water hose to supply water even more efficiently (but in my opinion you get innacurate reading of water flow since you get water pressure from the hose it self thats why I always choose a test bucket)
 
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