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Overheating.

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Chris55

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I recently brought a second hand 1986 Yamaha, (150) when I first started it, it wasn't pumping water. So straight away I changed the impeller, started it up today and no dramas with pumping water. I ran it for prob about 20 mins and noticed it was starting to get hot. The tell tail water was really getting hot, not warm, Hot! The heads were also getting to hot to touch, wondering where to go from here? Will it be the thermostats, or what's my next options? Cheers.
 
Chris55 said:
I recently brought a second hand 1986 Yamaha, (150) when I first started it, it wasn't pumping water. So straight away I changed the impeller, started it up today and no dramas with pumping water. I ran it for prob about 20 mins and noticed it was starting to get hot. The tell tail water was really getting hot, not warm, Hot! The heads were also getting to hot to touch, wondering where to go from here? Will it be the thermostats, or what's my next options? Cheers.
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Hi,
I'm no expert. I'm fighting the same issues on my 60HP Johnson. I'd try the thermostat first. If no luck there you may have blocked water passages (was the old impeller broken in pieces? Did you get them all?) if that seems OK it may be a head gasket, allowing hot exhaust gaskets to go where they are not supposed to. Take a look at
my post on "60 HP Johnson still overheating" good luck!
 
Not sure about the earlier Yams like yours, but the later ones have a thing called the "Pressure Relief Valve" (Poppit) that when stuck open will make the engine run hot at idle, but run OK at higher rpm's. At that age though it could also just be salt/corrosion build up in the water passages. Pulling the thermostats might give you some idea of how cruded up the passages are. There are instructions around somewhere for flushing with vinegar or other solutions to clean the passages.
 
Mine 25hp was getting hot and I found this behind my thermostat.....after I cleaned/flushed it all out it ran much cooler.

P4100245_zpsbba4ae7a.jpg



P4100244_zpsbae0d3ae.jpg
 
Thermostats and poppet valves (if you have them.) Pretty common thing. We always recommend changing them every other season. Yours being a 1986 could probably use some.
 
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