15 Johnson (1974) overheating

[twocyclemania]

Before I pull the power head I hope someone will know of an easier solution. The motor overheats. I've been testing it in a barrel. I replaced the pump and impeller. I also removed the head thinking maybe the thermostat was sticking; it had no thermostat. I installed a new thermostat and it's still overheating. Compression is good. I'm thinking the water tube grommet at the head. Anyone else with any other idea before I pull the head and if not how much of a job / any shortcuts in pulling the head? thanks

 

[emoney]

Re: 15 Johnson (1974) overheating

I'd pull the lower unit first and check the water tube. Make sure it's not clogged and is seating up into the block. They can get clogged or come loose on either end. It's an easier thing to inspect first, at least. Are you sure the impeller key is in place and it's spinning correctly?

 

[Rick.]

Re: 15 Johnson (1974) overheating

Agree with above. Also, the rubber grommet on the pump where the water tube inserts can be the source of the problem. It may have bent over if not lined up right. Last (and often the problem) when running in a barrel, make sure you have water well up the leg so the pump is well submerged. Best of luck. Rick.

 

[AlTn]

Re: 15 Johnson (1974) overheating

can only add this to the advice above....have read on here of one member fashioning a sharp cutting head on a metal rod <coat hanger I think> and , using a drill, routed out that upper grommet to increase water flow. Seems you'd have to backflush the rubber "cuttings" so they wouldn't get stuck in any of the cooling passages and if your cutting gets too far off course you're gonna have water going where you don't want it to. This offered as a FWIW...I haven't personally tried this.

 

[kbait]

Re: 15 Johnson (1974) overheating

I cleared an upper water grommet clog w/weed wacker string up the watertube. Sometimes you get lucky
You should be able to blow air up this tube w/o thermostat and get good flow through the powerhead.

 

[OptsyEagle]

Re: 15 Johnson (1974) overheating

Plus ... I believe they recommend that remove the lower unit to remove the powerhead anyways, so no downside to checking the above suggestions.

If you do take off the powerhead, Bktheking posted his procedure in post #9 of this thread. I used it on my '76 15Hp motor with great results. It took me a little more time then Bk suggests, but I suspect he has popped a lot more powerheads then I have (and ever hope to).

http://forums.iboats.com/showthread.php?t=373779&highlight=transom+clamps

If you do pop the powerhead, look at replacing the lower cranckcase seal as well. It is inexpensive and probably shot on that motor, by now. Easy fix once the powerhead is off the body.