Temp meter says hot at low speed

[mlaajanen]

Hi,

I have installed a temp meter(OMC original) on out Johnson 55 1980 short rigg.

At low speed it goes all they way to top reading(red) once speeding above 20 knots, the temp stays in the midle.

Could that be bad impeller just?

Michael

 

[jakedaawg]

Youll have to take it apart and look.

 

[mlaajanen]

Youll have to take it apart and look.

Where should I start?

 

[jakedaawg]

Drop the lower, remove impellar housing, inspect, replace impellar, test. Also inspect t-stat

 

[oldboat1]

Installed the gauge because you were having cooling issues? If overheating, it might smell hot, be hot to touch, no water at tell tale and none at exhaust port on the leg.

Impeller is always most likely. Replace it if it's been awhile, or if you run in river sand. Overheating before t.stat opens could also be an indication that the bypass in the housing is blocked, or that the t.stat itself is sticking shut -- or that water is not getting up and through the t.stat (which brings you back to the impeller as a likely cause).

 

[bob johnson]

id suggest changing the thermostats...the higher rpm might just be pushing the T-stat off the seat. usually at low speeds the temps SLOWLY rise and when they hit between 140 and 160 the T-stats open, and then the motor stops its temp rise......but if the t-stat is stuck, the temps keep rising because no cooling water is being allowed into the head....BUT if you give it more rpm and thus more water pressure...YOU PUSH the t-stats off its seat, and water rushes by.....but the water isn't going THROUGH the t-stat..... at least that's how all the t-stats I have seen work


bob

 

[mlaajanen]

N, I installed the temp meter just because I don't trust a on/off sensor and with temp meter I can watch what happends.

I will try and remove the lower part, the gearmechanism screw should it be completely removed or just loosen abit?

 

[bob johnson]

N, I installed the temp meter just because I don't trust a on/off sensor and with temp meter I can watch what happends.

I will try and remove the lower part, the gearmechanism screw should it be completely removed or just loosen abit?

id do a t-stat replacement first..... although there is not wrong with having a new water pump kit!!!

bob

 

[mlaajanen]

id suggest changing the thermostats...the higher rpm might just be pushing the T-stat off the seat. usually at low speeds the temps SLOWLY rise and when they hit between 140 and 160 the T-stats open, and then the motor stops its temp rise......but if the t-stat is stuck, the temps keep rising because no cooling water is being allowed into the head....BUT if you give it more rpm and thus more water pressure...YOU PUSH the t-stats off its seat, and water rushes by.....but the water isn't going THROUGH the t-stat..... at least that's how all the t-stats I have seen work


bob

You mean that the thermostat does not open as it should?
My experience with thermostat(in cars) is that they don't close as they should which means that the engine runs cooler that ij should, I have never seen a engine that overheats due to thermostat is outboards!

 

[bob johnson]

You mean that the thermostat does not open as it should?
My experience with thermostat(in cars) is that they don't close as they should which means that the engine runs cooler that ij should, I have never seen a engine that overheats due to thermostat is outboards!

I am saying that it MIGHT NOT BE.........

it is something you have to check. t-stats in outboards are different than in cars........

some t-stats in outboards have a spring that hold the WHOLE T_stat ASSY in place against a seal.....when the pressure is low the only way water gets by is if the temps rise and the t-stats opens as designed!!! at a specific temp...which is usually about 130 -160 degrees......but when the motor is running at 5000 rpms...not enough water can get through that little t-stat....so they are designed so the higher water pressure, pushes the whole t-stat off the seat and a larger volume of water rushed around and past the t-stat

bob

 

[oldboat1]

If removing the l.u., do not remove or loosen the Phillips head screw (you reference to a "gear mechanism screw"). Just the drain and fill screws -- normally large slotted heads. If you run in salt/brackish or sandy water, I would just replace the impeller and t.stat, and flush up the copper tube while you are at it -- and down from the t.stat housing.

 

[mlaajanen]

If removing the l.u., do not remove or loosen the Phillips head screw (you reference to a "gear mechanism screw"). Just the drain and fill screws -- normally large slotted heads. If you run in salt/brackish or sandy water, I would just replace the impeller and t.stat, and flush up the copper tube while you are at it -- and down from the t.stat housing.

No I refer to the hex screw under the carbs that connects the linkage with the lower unit.