Overheated Outboard Motor

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Neil McDonald

Neil McDonald

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Aug 19, 2004
239
Hunter 35 Vancouver, BC
The water cooling system on my dinghy's quite new 9 horse Yamaha 2 stroke outboard failed and, not at first noticing the problem, I continued to operate the engine...... which I assume then overheated. This winter I will of course fix the cooling. However thinking back on the experience, I realized that the hot and cold starting on this twin cylinder motor (whch had always been amazingly good) suddenly dramatically deteriorated after the overheating problem.

What are the usual consequences of overheating these motors? With the sudden onset of hard starting, I suspect the best case scenario might be a blown head gasket. :cussing:

Also a word of warning to anyone using a Davis outboard lifting harness. Don't let the harness strap cover the water cooling discharge port!!!!
 
MrBill_FLL

MrBill_FLL

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May 4, 2005
4,062
Macgregor 26d Ft Lauderdale, Fl
yes, the head gasket is where I'd start.

replace it and get a compression check.

if still bad, you might be able to shave the head.

otherwise, its tost IMHO. expensive lesson: change the impeller every year. (they rot from just sitting)

Actually I'm amazed it starts at all, after over heating it, so thats a good sign.
 
B

Barnacle Bill

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Jun 9, 2008
1,801
- -- -Bayfield
Most likely your water pump impellor is bad, or something got into the intake part of the system so water was blocked, which eventually will destroy the impellor. The worst scenario is if your head is warped due to accessive heat. Is the head discolored? If so, not a good sign. Usually if the head gasket is bad, you will get white smoke (steam) out of the exhaust suggesting that water is leaking into the cylinders. If your head is warped, then this will also happen and either you need a new head, or it has to be ground down so it is flat again by a machine shop taking into consideration proper clearances for the engine.
 
T

tommays

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Oct 2, 2006
1,517
Jboat J24 commack
Blocking the pee hole should NOT overheat the motor as it is just a flow indcator and the bulk of the water runs down the leg and out the exaust
 
thinwater

thinwater

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Mar 26, 2011
3,717
Corsair F-24 MK I Deale, MD
The 2 problems could be unrelated.

Neil McDonald said:
The water cooling system on my dinghy's quite new 9 horse Yamaha 2 stroke outboard failed and, not at first noticing the problem, I continued to operate the engine...... which I assume then overheated. This winter I will of course fix the cooling. However thinking back on the experience, I realized that the hot and cold starting on this twin cylinder motor (whch had always been amazingly good) suddenly dramatically deteriorated after the overheating problem.

What are the usual consequences of overheating these motors? With the sudden onset of hard starting, I suspect the best case scenario might be a blown head gasket. :cussing:

Also a word of warning to anyone using a Davis outboard lifting harness. Don't let the harness strap cover the water cooling discharge port!!!!
Click to expand

How does the engine run once started and warm (I'm assuming you've replaced the impellor by now)? If so, it may well be a carb problem.

I'm not saying the other posts are wrong, I'm just saying that 2 things can happen a the same time, and the extra heat would not have helped the gas in the carb any. I've overheated a few engines over the years (many years) and I know that the carb often got gummed in the process, while the engines were never damaged... but overheating is also a matter of degree.
 
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