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post #1 of 8 Old 07-18-2008 Thread Starter
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Small outboard motor question for the maintenance experts.

I own a 2 cycle, 1996, 15hp Yamaha outboard engine (model #15MLHU). This engine is operated in 53 F +/- degree salt water. After a period of normal use (on a small open boat-not the auxiliary engine of a sailboat) and the engine is OFF and tipped up and out of the water, when I reach back and touch the lower housing that houses the lower gear lubricating oil, how hot should the exterior of the housing be to the touch? In my case it was uncomfortably warm/hot to the touch. That didn’t seem right to me but I want to run the question by the experts here. What is “normal”?
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post #2 of 8 Old 07-18-2008
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The housing was hot to the touch? I've had some warmth, but nothing uncomfortable on the housing. I'd try the cheap fix of washing out the old grease and repacking to see if that fixes it. Dirty, but cheap.

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post #3 of 8 Old 07-18-2008
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In my experience they can get pretty warm, but it shouldn't be that hot. Are you touching it down by the gears directly in front of the prop? Remember that exhaust does flow though the lower unit. I'd change the gear oil. If it's burned, or milky, or contains a lot of metal (a small amount is normal) you have a problem.
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post #4 of 8 Old 07-18-2008
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Quote:
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? In my case it was uncomfortably warm/hot to the touch. That didn’t seem right to me but I want to run the question by the experts here. What is “normal”?
I had a 9.9 of similar vintage (stolen ).
The 9.9 is the same as the 15 with the only difference being a larger carb opening and larger ports.

Normal use (wide open on 16ft Jon) left the upper part of the lower housing (the part below the actual motor part) as you describe.

Obviously you have good "pee" water and the exhaust is coming out the prop when above idle, right?
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post #5 of 8 Old 07-18-2008 Thread Starter
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You two are right my next step will be to change out and inspect the the grease. Also SteveInMD you had a good point about the exhaust flowing out of the prop. I was not touching directly in front of the prop but the main housing itself where the gears that transfer the power from the drive shaft to the propeller live. Thanks for your time and information!
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therapy23

Yes I have good "pee" water. In fact I had just changed out the water impeller. I bought this engine used and try to take meticulous care of it. I only get to use it for a week or two each year. It gets flushed thoroughly with fresh water, the fuel system run dry, fogging oil added to the carburetor and intake system as well as the cylinders, sprayed with corrosion inhibitor and it is stored inside upright on an engine stand. Up until this year it has been bulletproof.

This year I did not have “pee” water initially and shut it right down (less than a minute of run time). I assumed a failed impeller so I replaced it. When I opened it up it turned out that there was nothing wrong with the old impeller. It was clean, flexible, complete and properly mounted. So, I had to have had some sort of obstruction somewhere internally. I had cooling water flowing out of every other water orifice except the “pee” hole. The tube connecting the “pee” hole to the engine was clear as was the plastic “pee” hole assembly itself, that left the obstruction to be located somewhere inside the power head. With a new impeller and water flowing I had the confidence to run up the speed and eventually I got a drip out of the tube that connects to the “pee” hole. A little longer and I had a powerful stream. But I never saw anything obvious come out.

So the next time I am up there (San Juan Islands-Washington State) I will replace the thermostat and the lower unit gear oil.
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therapy23

Yes I have good "pee" water. In fact I had just changed out the water impeller. I bought this engine used and try to take meticulous care of it. I only get to use it for a week or two each year. It gets flushed thoroughly with fresh water, the fuel system run dry, fogging oil added to the carburetor and intake system as well as the cylinders, sprayed with corrosion inhibitor and it is stored inside upright on an engine stand. Up until this year it has been bulletproof.

This year I did not have “pee” water initially and shut it right down (less than a minute of run time). I assumed a failed impeller so I replaced it. When I opened it up it turned out that there was nothing wrong with the old impeller. It was clean, flexible, complete and properly mounted. So, I had to have had some sort of obstruction somewhere internally. I had cooling water flowing out of every other water orifice except the “pee” hole. The tube connecting the “pee” hole to the engine was clear as was the plastic “pee” hole assembly itself, that left the obstruction to be located somewhere inside the power head. With a new impeller and water flowing I had the confidence to run up the speed and eventually I got a drip out of the tube that connects to the “pee” hole. A little longer and I had a powerful stream. But I never saw anything obvious come out.

So the next time I am up there (San Juan Islands-Washington State) I will replace the thermostat and the lower unit gear oil.
Good old Yammy's

T-stat and gear oil can't hurt. Gear oil once a year, used or not, is recommended by many.

I don't think there is anything wrong with the motor.

When I store my outboards in FL (lots of bugs) even for a short time (two weeks can do it) what I do is stick a pipe cleaner in the pee hole. Lots of bugs love this hole. Some build stuff that "melts" easily and some build "cement" structures. None build if the hole is plugged!
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post #8 of 8 Old 07-19-2008
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I'd second on the thermostat. If she wasn't peeing then suddenly started, that's your blockage most likely. I've had the same issue with my 15 HP Johnson You can check the thermostat on the stove with a pot of water and a thermometer. Observe as temp comes up and when the thermostat opens. Hang it off the side so it's not sitting on the bottom of the pot. Or just put a new one in. But science projects are always fun.
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