# Overheated 7.5hp Outboard



## Fletch_W (Feb 28, 2012)

It's a Force/Merc gamefisher, 1989. I had it up and running in a trash can at medium throttle in gear (after cleaning the carb, fresh gas and oil 50:1, cleaning plugs, spray seafoam). 

Water spitting out of exhaust as normal, coming out of "tell-tale" hole like normal. I walked inside, bragged about my accomplishment, opened a beer, walked back outside, and the motor had stopped running. There was a lot of smoke, I just figured Sea Foam. 

I finally got it started back up, and noticed no more water coming from exhaust, and the tell-tale hole was under water at this point so I reached down to tilt the motor up high enough to check it (in neutral, of course), and it burned my hand... and no water coming from tell-tale hole either. I cut the motor off. Smoke started coming out of the carb throat and of course, exhaust. Smell of burning, bad burning. 

In other words, I overheated this motor. The impeller is ordered, I'll have it in a little over a week, but my question is more of a discussion. 

What are the chances that irrepairable damage has been done to this motor?

What are the chances that damage, but repairable, has been done?

Reeds? Rings? Gaskets? What all kinds of stuff is inside of that magic chamber that would be quickly burned up and ruined by overheating? 

How long was it overheating you ask? Not sure... water was flowing when I went inside, maybe 5 or ten minutes before I noticed it was no longer running. Then another 3-5 minutes after I restarted it before I noticed how hot it was and no water flow. 

Discuss. 


PS.. for any of you banned people that might be reading this, feel free to email me.


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## Davis31052 (Feb 29, 2012)

If it restrarted after shutting off, odds are no real damage was done. Sounds like the impellor might have come apart or just stopped pumping. Put a new one in and start it up again. Be sure to clean out any broken pieces that may have gotten inside the water tube up to the power head.  Let us know what the results are.


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## Heron2000 (Feb 29, 2012)

i agree with davis31052


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## GT-40 GUY (Feb 29, 2012)

Bet you a nickel you put the impeller in backwards.  

Ask me how I know.

gt40

PS: Hope you don't.


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## Fletch_W (Feb 29, 2012)

My father is one step ahead of you. He changed the impeller on this in 2004, I consulted him. He made sure to mention to put it in the right way, and gave me some details. I'm glad he did, it never would have occurred to me when looking at a perfectly symmetrical piece of rubber.


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## Redbow (Mar 2, 2012)

An ice bag wrapped around the lower unit on a 35 Evinrude I had once without me knowing it. The motor stalled and started steaming badly. The motor ran so hot it even melted the plastic fitting in the engine block that shoots out a stream of water to let you know the water pump is working. I thought I had ruined the Evinrude but after it cooled down we made it back to the boat ramp which was several miles away. I had a new water pump impeller installed and used that motor for several years after it ran hot. Yours might do the same...Good luck...


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## j_seph (Mar 2, 2012)

If it is like my 7.5 merc mid 80's model there is a fine hole in the bottom cover where the water comes out at. Mine would quit pumping or get very little water coming out there. When it did it would be some small trash that would fit through the tube but would not pass through the small hole in the bottom cover.


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## Davis31052 (Mar 2, 2012)

Oh yeah, for what its worth, running an outboard in a drum or on water muffs, over idle, for anything more than a carb adjustment really isn't good.  

Two stroke motors are designed to run at high RPMS.  Running at idle in a stationary situation does not provide the necessary water flow needed to cool the engine and causes lots of unburned fuel/oil to accumulate in the cylinders and exhaust system.

 Best to just get it where it will start and run in the drum or on the muffs. Then put it in the lake or pond and adjust under a load  utilizing the manufacturers recommmended procedures.


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## j_seph (Mar 2, 2012)

Looks like in a drum it would also begin to pump unburnt oil through water pump and heat the water in the drum up as well


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## greg_n_clayton (Mar 2, 2012)

Davis31052 said:


> Oh yeah, for what its worth, running an outboard in a drum or on water muffs, over idle, for anything more than a carb adjustment really isn't good.
> 
> Two stroke motors are designed to run at high RPMS.  Running at idle in a stationary situation does not provide the necessary water flow needed to cool the engine and causes lots of unburned fuel/oil to accumulate in the cylinders and exhaust system.
> 
> Best to just get it where it will start and run in the drum or on the muffs. Then put it in the lake or pond and adjust under a load  utilizing the manufacturers recommmended procedures.



I have had 'em run good in the yard,then, put them under a load and things changed....lots !!


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## Fletch_W (Mar 2, 2012)

The nearest pond is a solid 40 minute drive. 

I have read about idling not good over long periods, in regard to spark plug life and performance. That's why I revved it up as much as I could without all the water splashing out of the trash can, in gear so there is some "load", before I walked away. I'm glad I did it too... or I would have been up Oconee River or in Ft. Yargo under a severe t-sorm when the impeller failed. 

Ultimately, I just need to not go 8 years between impellers. Thanks for the info and encouragement yall! My new impeller shipped yesterday.


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