# 1979 15HP Evinrude Overheated



## Vermonster (Sep 19, 2012)

Last month I took the boat out for a speed test. I was lazy and waited until the middle of the day which meant there was traffic on the lake and a bit more chop than I would prefer. I made one run and the boat was moving right along. I turned her around and took out the GPS and made another go. It read 20-22 MPH but the engine started to sound like it was bogging down in the middle of the run and the speed steadily dropped. I backed off the throttle, and it just stalled out. Then there was a bit of smoke which is always comforting. I limped into a cove with the trolling motor and anchored up. I pulled the cover off (which was damn hot) and saw that the wire shielding had melted (which was what smoked). I let it sit for about 10 minutes and it still didn't want to start. It started to catch on the last couple pulls and then the pull cord snapped out of the handle. I gave up and limped back to the launch on the trolling motor.

1. Water was definitely coming out the pee hole.
2. It was 90+ on the lake, and the water temp was about 82.

When I got the boat back on the trailer I threaded the pull cord through the handle again. Problem 1 fixed with help from a ball point pen.
When I got home, I busted out the hose and the muffs. The engine started up on the 2nd pull. Water was coming out of the pee hole. I ran it for about 5 minutes and had no issue.

Today (after about a month and some reading), I started up the motor and ran it with the muffs for about 5 minutes at idle, and another 5 a mid throttle and another 5 at 3/4 throttle. The water coming out of the pee hole was cold at first and then got warm, but never got hot. No smoke (other than exhaust). I pulled the cover off afterwards and could touch the head as well.

I picked up an water pump kit because I know it is likely due for one. I've had the boat over a year and haven't replaced it. I have no idea when the previous owner changed it last, but it's run perfectly up until that last trip.

I'd like to know what happened, because I don't like surprises. I figured it was the water pump/impeller or the thermostat, but it seems to not be an issue now. Before I started pulling everything apart I thought I would ask you fellas 

Here's a shorter video of it running today:
https://www.youtube.com/watch?v=-RVbBE-kWk8


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## jasper60103 (Sep 19, 2012)

The intake could have been blocked by weeds? Sometimes they wrap around the gear case. Just a guess.


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## Talons (Sep 19, 2012)

Did you get shallow? Could have been mud. Did you gradually bring her up to speed? My 200 HP Evinrude would NOT let me "Floor it" without me getting the buzzer... ALWAYS! Gradual speed increases were okay, and if you were already up on plane, fine, but from a dead stop to full power was a no-no.

If it is fine now, take it back to the lake and see if it does it again... If not, then you are probably good to go. I have had weed, mud, sand, etc. clog it up for a bit, but usually it is only a little while.

Talons


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## Vermonster (Sep 19, 2012)

Appreciate the help! I didn't have it shallow, and I wish this lake had some weeds in it! It would make it more fun to fish. Cover is hard to find. I brought it up to speed slowly, but had it wide open when it started to bog down. I'm certainly more familiar with the parts of the motor now after watching all of the videos and reading the manual. I'd prefer not to limp back with the trolling motor, but it beats paddling.


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## Pappy (Sep 20, 2012)

Probably won't like this answer much. 
What happened is that your cooling system was blocked, probably temporarily. 
Second - your engine got hot enough to seize. That is what was happening when it was slowing down on its own and then abruptly stopped when you reduced power. Not good!
Depending on how hard it stuck and the resultant damage you may be okay or you may start experiencing hard starts when the engine is warm and normal starts when the engine is cool. Read your own post again and you will see that scenario. 
Would definitely add a little more oil to the fuel and idle it for a long time if you have no intention of doing an inspection after the overheat. 
When you say you got a kit for the water pump you should be getting the complete pump if there are any grooves in the upper cup or lower plate that you can easily feel with a fingernail. 
If the engine was a salt water engine there may be another reason for your overheat and at this point I will definitely recommend that you replace the upper water tube grommet at the very least as it will have melted and is now deformed and probably will be a partial restriction to flow from now on. Not a difficult job but a little time consuming.


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## Vermonster (Sep 20, 2012)

Thanks Pappy, 
I got the complete water pump/impeller kit. I'm also running the original plugs that were in the motor when I purchased it over a year ago. I don't think they were new when I purchased by any means. I've pulled them out and looked at them and they look good, but I've already got the replacements on hand. The other thing is I know I need to replace the gas (it's old). I thought about running a compression test as well just for my own piece of mind. 

Things that I'm planning on doing:
Possibly running a compression test.
Replacing plugs (likely 5+ years old or more).
Replacing Water pump/impeller with kit (likely older than the plugs).
Replacing gas with ethanol free mix. 

The engine has never been in salt water - that I know.

The kicker is that it has just run so well for me I didn't want to cause more problems. Then I bring it home and test it twice (a month apart) and it runs fine.


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## Talons (Sep 20, 2012)

Could have been vapor lock.


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## 96redtoy (Sep 20, 2012)

It might not have been a cooling problem, but a leaning out problem. I say the chances of this are slim but might want to look into it a little. Make sure that the engine isn't getting air from anywhere but the intake on the carb. (ie cracked gasket between carb and manifold, cracked fuel lines, ext) Also someone could have messed with the high end adjustment :shock: and you wouldn't have been the wiser. 

Just something to think about, but my money would be on the cooling.


I would also pull the thermostat and make sure its opening fully. Heat up a bowl of hot water in the microwave and drop the thermostat in it. Watch for it to open then close as the water cools. Do this a few times to make sure it doesn't get hung up. :wink:


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## tnriverluver (Sep 20, 2012)

Replace the thermostat!!! I had a very similar thing with my 1975 25 Evinrude very first time out. Turned out to be a chunk of silicone blocking the intake to the thermostat from where the previous owner replaced the head gasket and exhaust manifold. Very small passage in and out of there.


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## Pappy (Sep 21, 2012)

Talons said:


> Could have been vapor lock.


Hmmm when was the last time a vapor lock caused smoke and melted wire insulation.....................................and a seizure. 
Vapor lock (heat soak) becomes evident on start up after a shut down period of around 15-20 minutes or so and will usually result in lack of acceleration until cooler fuel has replaced the hot fuel in the carb bowl. 

Also, it was not a leaning out issue. That will not melt wires. If there was a failed gasket on the intake the engine would exhibit a lean sneeze at idle or not run on that cylinder. Plus, there is no high speed adjustment on that engine. It is a fixed jet. 

If you are really interested in looking for damage then do your compression check but you may also want to pull the intake by pass covers and look over at the exhaust side of the cylinder walls. Chances are they are scuffed. Hopefully just lightly. 
Do not forget about the grommet at the top of the water tube either. Guarantee that is deformed and may be a restriction to flow volume at higher RPM and requirements.


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## Charger25 (Sep 22, 2012)

Pappy said:


> Talons said:
> 
> 
> > Could have been vapor lock.
> ...





tnriverluver said:


> Replace the thermostat!!! I had a very similar thing with my 1975 25 Evinrude very first time out. Turned out to be a chunk of silicone blocking the intake to the thermostat from where the previous owner replaced the head gasket and exhaust manifold. Very small passage in and out of there.




I agree.......The first thing I'd do is pull the T-stat and go from there. K.I.S.S. (keep it simple )


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## Vermonster (Sep 22, 2012)

Thanks guys! I appreciate the help, and I'll post what I find in my investigations!


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## nomowork (Sep 24, 2012)

Just my 2 cents but, I had bought older 15hp Johnson (didn't know the year of it) that ran great for two years then started having heating and peeing problems. Yes, I changed the impeller and all seals in the lower unit including the prop shaft, etc. I ran great for awhile then started overheating again and not peeing. I dropped the lower unit and spun it with an electric drill on the drive shaft while lowered into a barrel of water. The water pump was still putting out so then turned my attention to the upper part of the engine. Shot some water up the pickup tube and no water was coming out by the thermostat. Shoved a coat hanger wire up the tube (be careful of seals at the top) and that cleared an obstruction. Put everything back together and was peeing fine. A little while later it started over heating again, so this time pulled the head off (which is fairly easy) and the gasket was toast. Replaced the head gasket and no more over heating problems.

This is just my experience but this motor was supposedly rebuilt. :shock:


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## Talons (Sep 29, 2012)

Pappy said:


> Talons said:
> 
> 
> > Could have been vapor lock.
> ...


The engine didn't start for him on the water because after it overheated, it was hot enough to cause vapor lock. Then his cord broke. By the time he got home and fixed the rope the lock was gone and it started right up.

You are right, vapor lock doesn't melt wires, but that kind of temp def turns gas to vapor. Im sorry for not stating exactly what I meant. I thought there was a question as to why it would not start after the overheat, but then started right up at home. I might have just thought the question was posted. 

Talons


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## Vermonster (Sep 30, 2012)

There was definitely a cooling problem. I haven't gotten to the impeller/water pump yet, but I did replace the thermostat today. You might say it was looking a bit rough compared to the new one (without the seal):




When I took off the thermostat cover (which is the awesome one located on the bottom-not fun), I noticed that some of the heat plastic wrap on the wires were melted to that as well. 

I also replaced the plugs which I had to order online because I couldn't find anybody that carried them near me.

Next up waterpump and impeller - and then the yard test before the lake test. 
Thanks again for the help!


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## Pappy (Oct 3, 2012)

Your thermostat was stuck in the open position, which it was designed to do. 
Notice once again, no mention of the water tube grommet. Almost guarantee that part is toast. Your engine may cool somewhat from this point on but will have a built in restriction to water flow from now on. Look at it like a water hose with a partial kink in it.


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## Gator McClusky (Oct 3, 2012)

Pappy said:


> Your thermostat was stuck in the open position, which it was designed to do.
> Notice once again, no mention of the water tube grommet. Almost guarantee that part is toast. Your engine may cool somewhat from this point on but will have a built in restriction to water flow from now on. Look at it like a water hose with a partial kink in it.



How hard is it to get to this grommet Pappy? I have a similar situation with a similar motor. Where do you start?


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## Pappy (Oct 4, 2012)

Pull the gearcase and powerhead. Simple. 
Nice thing about it is that the fuel lines can be easily replaced when you do it as well as shift shaft can be disassembled and lubricated. Pan can be cleaned up, etc.
Powerhead has more fasteners but is no more difficult to remove than the gearcase is. Have a few more items to remove (fuel lines, throttle linkage, etc.) but thats it. Some years have a single grommet and some have two. Once the powerhead has been removed it is a two minute job to replace it.


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## Gator McClusky (Oct 4, 2012)

Pappy said:


> Pull the gearcase and powerhead. Simple.
> Nice thing about it is that the fuel lines can be easily replaced when you do it as well as shift shaft can be disassembled and lubricated. Pan can be cleaned up, etc.
> Powerhead has more fasteners but is no more difficult to remove than the gearcase is. Have a few more items to remove (fuel lines, throttle linkage, etc.) but thats it. Some years have a single grommet and some have two. Once the powerhead has been removed it is a two minute job to replace it.



Got it! I will start on this next week.


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## Vermonster (Oct 6, 2012)

Small update from this week:

Tried to fire up the motor after swapping out the plugs and changing out the thermostat - NO SPARK. I looked everything over for days and still couldn't get a spark. 

Finally today I pulled the cables apart and noticed that one of the 4 pronged plugs on the motor had a prong that was completely bent and not in the hole/receptacle. You could even see where it had been jammed in there on the other side of the plug. I straightened it out and had a nice blue spark. I tightened the plugs and it fired right up. 

I noticed that since changing the thermostat, I can actually feel the differences in temps when it goes warm and cold. I assume that this is when the thermostat opens up and closes. I also noticed that the telltale/pee hole is probably pumping twice as much water as it was previously with the old thermostat. I haven't even changed the impeller/water pump yet. I decided I'm going to take it to the shop anyways and have them take care of the following:

1. Water pump/Impeller
2. Lower Unit oil change
3. Check the grommet on the water tube
4. Fix the starter rope (it doesn't like to rewind all the way immediately but will over time).

I think I could manage all of those things, but it would take a couple weekends that I would rather spend fishing, so I'm taking it in. 

I appreciate the help that's always here!


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## jasper60103 (Oct 6, 2012)

Good job on tracking down the cooling and spark issue. =D> 
Keep us posted.


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## cajuncook1 (Oct 9, 2012)

Pappy said:


> Your thermostat was stuck in the open position, which it was designed to do.
> Notice once again, no mention of the water tube grommet. Almost guarantee that part is toast. Your engine may cool somewhat from this point on but will have a built in restriction to water flow from now on. Look at it like a water hose with a partial kink in it.




*
Please Please, heed Pappy's advice on this*. I know it seems like a big chore, but investigating will insure your motor cools properly and that you will visually see the condition of both water grommets.

Here a couple of links that will help walk you through the process and gives pictures and explanations. 

*Lower unit*

https://www.leeroysramblings.com/Lower_unit.htm

*Water Circulation & Associated Problems* (please through this link very well)

https://www.leeroysramblings.com/water_circulation.htm


Here is the rest of the link with loads of information.

https://www.leeroysramblings.com/OMC_info/OMCinfo.htm


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