EVINRUDE 115hp Model # 115793S

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flathead6990

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Hello :) I have an evinrude 115hp. I was out on lake Friday night & was running at WOT & heard a buzzing noise and my temp sensor was going off in my control box. I have had this boat & motor for 8 years with no overheating problem. The temp gaduage needle did always run to the end of green to the little white line before the red/overheating mark. I Stopped the motor right when I noticed the alarm was going off. I Ran it for like 10 minutes the next day WOT 5300RPM & it started overheating again (I killed it before temp alarm).. Today I started it on muffs in my driveway & it didnt overheat??? Cant put it in gear on muffs so pulled start lever to increase the idle to like 4500rpm for like 5-10 min & it didnt seem to overheat.. I pulled the water hoses & water was coming out evenly on each side (v4 cyl)??? Please Help why would my motor have overheated??? What else can I check or do?? & this year motor has no tell tale.. Thanks in advance for any responses!! ;-)
 
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flathead6990

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Re: EVINRUDE 115hp Model # 115793S

Just thinking might have been bad gass/oil mixture?????? Too lean??
 
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emdsapmgr

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11,551
Re: EVINRUDE 115hp Model # 115793S

A 1977 model. Your model number was one of the last for the single vernatherm (thermostat.) (Some other 1977 models used the newer, dual thermostat system.) I'd look at the vernatherm housing. It's possible that one of the nylon valves in the stat housing has become heat-deformed and may not be functioning properly when planing. Also possible you've sucked some weeds, sand, debris into the housing-restricting water flow. (common on fishing engines used is shallow waters.) In any event, you'll want to get into that stat housing, replace the vernatherm and esp-visually check the nylon valves to see if they are heat-deformed, possibly restricting water flow.
 
toddschubert

toddschubert

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Sep 3, 2011
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504
Re: EVINRUDE 115hp Model # 115793S

I believe that motor has whats called water deflectors in it. They are little rubber tubes that fit between cylinder walls on each side. They get flattened out and do not do their job with time. It requires removing the heads but the parts are cheap. 2-deflectors and gaskets. Under $100 Gaskets being most expensive at around $50.
This can cause overheating under load.
 
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flathead6990

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Re: EVINRUDE 115hp Model # 115793S

Thank You!! Where is the thermostat / housing?? & Have to pull the piston heads/covers requiring new gaskets to check the deflectors?
 
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boobie

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Re: EVINRUDE 115hp Model # 115793S

Keep on running it at 4500 rpm in neutral and you'll be doing a power head job.
 
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emdsapmgr

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Re: EVINRUDE 115hp Model # 115793S

You can see the factory exploded parts diagram for your engine. It's very helpful to see how everything goes together. Check out this website: epc.brp.com. You'll find the thermostat housing on the "exhaust housing" parts diagram. Be sure you are using the correct diagram-the factory breaks them by the exact model number.
 
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flathead6990

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Re: EVINRUDE 115hp Model # 115793S

emdsapmgr said:
You can see the factory exploded parts diagram for your engine. It's very helpful to see how everything goes together. Check out this website: epc.brp.com. You'll find the thermostat housing on the "exhaust housing" parts diagram. Be sure you are using the correct diagram-the factory breaks them by the exact model number.
Click to expand...

I checked the diagram and pulled the thermostat housing but it has part #318398 and it dosent even show that being the part # on the diagram?? Is the vernatherm supposed to be stuck/attached to the housing? Is the pin also supposed to be attached to the housing? Mine seem to be just one piece with the housing or it has all corroded together. I dont want to force anything apart if they are not different pieces.. :confused:
 
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flathead6990

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Jul 19, 2010
Messages
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Re: EVINRUDE 115hp Model # 115793S

emdsapmgr said:
A 1977 model. Your model number was one of the last for the single vernatherm (thermostat.) (Some other 1977 models used the newer, dual thermostat system.) I'd look at the vernatherm housing. It's possible that one of the nylon valves in the stat housing has become heat-deformed and may not be functioning properly when planing. Also possible you've sucked some weeds, sand, debris into the housing-restricting water flow. (common on fishing engines used is shallow waters.) In any event, you'll want to get into that stat housing, replace the vernatherm and esp-visually check the nylon valves to see if they are heat-deformed, possibly restricting water flow.
Click to expand...

Got into the vernatherm housing and appears to be part of the housing?? Or is it a separate part? Checked the nylon valves and they appear fine. The check valve and spring are good looking. Should the spring vernatherm valve move/push in like the check valve?? :eek:
 
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flathead6990

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Jul 19, 2010
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Re: EVINRUDE 115hp Model # 115793S

ok got vernatherm out and is old and is water corroded.. What does a vernatherm do?? How would I check the one I pulled? Help PLEASE?!?!?!?!?!? Tried to post picture but no luck doing so... How does one post picture on this forum???
 
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rockyrude

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Re: EVINRUDE 115hp Model # 115793S

That vernatherm does look pretty corroded. The pin "pops" up at temp pushing the nylon disc up opening the water passage. You could test it in a pan of water and see if it opens up around 140 degrees, but since you say this is an intermitent problem, I'd just replace it.
 
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flathead6990

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Jul 19, 2010
Messages
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Re: EVINRUDE 115hp Model # 115793S

Thank You rockyrude!! Yes really old/corroded. Testing now!! Will post results.. Think my deflectors are bad now it has overheated or should I just start with the thermostat/vernatherm???
 
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