Overheating

Robert II

Cadet
Joined
Aug 17, 2017
Messages
6
Help- my 15hp 1 year old engine is overheating- Validated function of thermostat and water to case. Tested thermostat in pot opens at 140f- ran engine with out thermostat got good water coming out. Tell tale strong and increases with RPM's. 20 minutes running in lake with 60 degree water and engine stalls... engine is blistering hot- probed at 200f at valve cover with tell tale water at 110f. When I turn engine off and feel residual tell tale water it get blistering hot as it slows coming out...??? Any ideas or suggestions Please?
 

Robert II

Cadet
Joined
Aug 17, 2017
Messages
6
The guy I bought it from said he just replaced impeller. He had it on a 15ft Gregor and trailer I bought from him.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
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Jul 23, 2011
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47,296
here is my guess.

prior owner had issue, impeller had failed and parts of it got lodged within the motor

puts in new impeller and sells it

you buy it, and it overheats

my suggestion, pull the lower unit, inspect the raw water pump, back-flush everything and start looking for the cause of the problem before ever firing up the motor again.
 

Robert II

Cadet
Joined
Aug 17, 2017
Messages
6
here is my guess.

prior owner had issue, impeller had failed and parts of it got lodged within the motor

puts in new impeller and sells it

you buy it, and it overheats

my suggestion, pull the lower unit, inspect the raw water pump, back-flush everything and start looking for the cause of the problem before ever firing up the motor again.

Ok thanks- What would be the best practice for a "backflush"? Run water/ air through thermostat opening?
 

brim_buster

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Jul 9, 2013
Messages
1,203
my thing is that you stated you have a very strong telltale stream and it increases with the RPMs. That would tell me that water is flowing good through the block. And I always remove a thermostat. Thats just me. So im thinking to myself what is causing my block to get overly hot if I have good water circulation?Oil / gas mixture would be one thing. Burning too hot in the cylinder? But yours is a 4 stroke Im sure so that eliminates that. I would recheck the impellor to make sure its installed correctly like Danforth stated but myself am puzzled that you have good circulation. Take the head off and check all your passages as well.
 

Robert II

Cadet
Joined
Aug 17, 2017
Messages
6
No Title

my thing is that you stated you have a very strong telltale stream and it increases with the RPMs. That would tell me that water is flowing good through the block. And I always remove a thermostat. Thats just me. So im thinking to myself what is causing my block to get overly hot if I have good water circulation?Oil / gas mixture would be one thing. Burning too hot in the cylinder? But yours is a 4 stroke Im sure so that eliminates that. I would recheck the impellor to make sure its installed correctly like Danforth stated but myself am puzzled that you have good circulation. Take the head off and check all your passages as well.

So maybe this will help- here is a pic of the amount of water coming out the hole where the thermostat would be. At idle-
 

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Robert II

Cadet
Joined
Aug 17, 2017
Messages
6
No Title

here is my guess.

prior owner had issue, impeller had failed and parts of it got lodged within the motor

puts in new impeller and sells it

you buy it, and it overheats

my suggestion, pull the lower unit, inspect the raw water pump, back-flush everything and start looking for the cause of the problem before ever firing up the motor again.

Update: Scott you were right!
Pulled the lower and found chunks of impeller in the water pump cap- Impeller was installed correctly. He put a new impeller in a housing that was clogged with previous impeller chunks!
 

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brim_buster

Lieutenant Junior Grade
Joined
Jul 9, 2013
Messages
1,203
Update: Scott you were right!
Pulled the lower and found chunks of impeller in the water pump cap- Impeller was installed correctly. He put a new impeller in a housing that was clogged with previous impeller chunks!
Life is good when its that easy
:)
 
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