Overheat Problem

[biffagump]

2001 Johnson 115 hp v-4
This motor idles fine on muffs with no overheat. The motor runs
fine on plane (3000 rpm) with no overheat. When the motor is in gear, at idle, the motor overheats. If I just bump up the throttle a little, the motor IMMEDIATELY cools down. I should mention that the motor idles at about 160 degrees when warmed up. Running on plane it is at about 140 degrees. It seems to me that at the present idle it simply is not turning the water pump fast enough to provide the minimum amount of water to keep the engine cool. Therefore, I am considering changing the timing just a bit to bump up the idle. There is no idle adjustment screw on this motor. Does this sound like a good idea? Thanks, Frank

 

[ob]

Re: Overheat Problem

No.What sounds like a better idea is to remove and replace the existing T/stats to allow better flow at low rpm.At higher rpm the spring loaded bypass feature of the T/stats allow for full flow.I would also recommend replacing waterpump.If yours is original,the cup and or impeller is likely worn.

 

[OBJ]

Re: Overheat Problem

I believe I would change out the impeller first. The symptoms posted are pointing toward the impeller. The "fins" on the impeller have lost there memory and will no longer spring out against the impeller cup which is needed at lower rpms'. At higher revs, even with the fins bent back, there is enough centrificle (sp) force to move the water up into the block and is why the block cools at higher rpms.

As ob posted, check the t-stat also if your not sure of the last time they were replaced. Can't hurt.

 

[biffagump]

Re: Overheat Problem

Thanks for the help. I already rebuilt the water pump so it looks like I will replace t/stats next. Frank

 

[OBJ]

Re: Overheat Problem

Sounds like a plan Frank....let us know how it works out.

 

[wisechips]

Re: Overheat Problem

The rule of thumb . Drop the uinit check the pump.

 

[clanton]

Re: Overheat Problem

Check for correct water pump housing.