1974 15 hp mdl 15404s getting hot HELP

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Whiskers

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Mar 17, 2012
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Location
Greencastle, Indiana
Hi everyone, i have this boat motor for about 10 years and it has been sitting for 7 and i figured id get her running and i rebuilt the carb, put new water pump plugs and so on but i took it out the other night and it over heated on me and melted my plug wires to the head. I fixed all that and i got the blubber hole spraying but it still gets very hot. i let it run to hot to touch and then watch it before it gets too bad but it still is hot enough to put a drop of water on it it boils the drop of water. Somebody told me its probley the thermostat but i don't have any idea where its at or how hard to change. any help from the many motor guys on here is very greatly appreciated.
 
Ok what brand of motor is it? I am not familiar with mdl..... #-o And yes, if it is pumping water out the pee hole but it is still running hot then the thermostat is not opening at all or not at the correct temp.
 
Ok there we go :) It is part #19 in this diagram and you will have to remove the water cover to get to it. Buy the gasket also because it will definitely need replacing.

https://www.boats.net/parts/search/BRP/JOHNSON/1974/15RL74S/CYLINDER%20%26%20CRANKCASE/parts.html
 
Almost forgot to tell you to get part #20 also.... you may have already known that but I thought I would mention it. Thermostat seal :)
 
Your welcome :) That's why we are all here.... to help one another. Try and soak those water cover bolts with penetrating oil over night. They are notorious for snapping off in the head due to years of corrosion :cry:
 
Yeah scrape the paint off the bolt heads (if there is any left) and spray them. Every couple hours or so spray again.... I also tap them lightly to try and loosen the crap between the threads. Even doing all of this you may still break them off, it is very common. When you go to put them back in you will want to coat them with anti seeze. Best case scenario if they break off, only the head of the bolt comes off. Then when you remove the cover there will be a piece that you can grab with vise grips..... a torch set will probably be required also to heat it before trying to remove it. But this is all hypothetical and I hope they come out easy enough for ya :)
 
So far you are on the right track with advice. However, when removing stuck bolts you can try the penetrating oil but if they still wont budge get at least a MAPP torch and heat the thread area until the paint is burned off or until the bolt starts moving. When the bolt stops rotating apply more heat.........go slowly and gently.
Never apply an anti-seize compound to an outboard unless you can find it with no metallic make-up. Anti-seize will add a third metal to the bond between the stainless bolt and the aluminum casting and immediately begin to corrode the casting. One of the best thread lubricants to use these days is the common teflon thread sealant (PTFE) in liquid form. Even in salt water applications this stuff is used below the waterline on gearcase attachment hardware and water pump bolts and these bolts can be removed easily 2-3 years down the road. Freshwater much longer.
 

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