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Charles, Marine Mechanic
Category: Boat
Satisfied Customers: 3869
Experience:  US Navy (Ret) Certified Mercury Marine Tech with over a decade of repair experience.
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Over heats at slow speeds and at idle, cools fine at gher

Customer Question

over heats at slow speeds and at idle, cools fine at higher speeds, Have new water pump , checked thermostats and are fine. The motor is a 2002 Honda 225 hp with 140 hours
JA: Sometimes boat issues seem like they'll be really complicated, but end up being easy to fix. The Marine Mechanic I'm going to connect you with knows all the tricks and shortcuts. Tell me a bit more about what's going on so the Marine Mechanic can help you best.
Customer: alarms go off when it is idling, I have checked the manifold temp with a laser thermometer and it shut s off at 200 degrees. it seems to be getting enough water as it is coming out of the weep hole in a steady stream.
JA: Is there anything else the Marine Mechanic should be aware of?
Customer: this is about it
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Submitted: 1 year ago.
Category: Boat
Expert:  Charles replied 1 year ago.

Hello, my name is***** will assist you.

When was the last time the cooling system was serviced?

Customer: replied 1 year ago.
the system was flushed last fall before storage
Expert:  Charles replied 1 year ago.

What about replacing the impeller?

Saltwater boat?

Customer: replied 1 year ago.
Just replaced impeller, fresh water boat
Expert:  Charles replied 1 year ago.

Is the overheat light on the key switch panel the one that is coming on?

Customer: replied 1 year ago.
it is light comes on and buzzer goes off after it has been idling for about five minutes
Expert:  Charles replied 1 year ago.

How long has the issue been going on?

Customer: replied 1 year ago.
all last season ,
Customer: replied 1 year ago.
We took it into a boat repair shop and they replaced the impeller and they could not figure out what was wrong, I replaced the same impeller again this spring.
Expert:  Charles replied 1 year ago.

When you shot the temps, did you do so at or near the temp sender on each cylinder head?

Expert:  Charles replied 1 year ago.

When you replaced the pump, did you ensure that the sealing o-ring was installed in the pump housing?

Customer: replied 1 year ago.
all the O-rings and gaskets were in there place, I also by- passed the pump and put the water hose direct in to the water pipe that the pump goes into and it still heated, also tried without thermostats installed and the same thing happened it over heated in the same amount of time.
Expert:  Charles replied 1 year ago.

Inspect the harness going from the exhaust manifolds heading to the ECU. Make sure that there is no melted wiring or any parts of the loom.

Customer: replied 1 year ago.
I checked the temperature of the manifolds with a laser pyrometer and the right one was at 200 degrees when it shut down and the left one was at 190, I will check the wiring tomorrow, but I don't think t hat there is anything wrong with it
Expert:  Charles replied 1 year ago.

200 wil trigger the alarm. Or it should. Have you tried to run the engine for a minute with the t-stat housings off and check the water flow to them?

Customer: replied 1 year ago.
Will do that today, Thank You
Expert:  Charles replied 1 year ago.

Your welcome

Customer: replied 1 year ago.
just ran motor with thermostats out and housings with hose attached, absolutely no water coming out at idle, it comes out rather sporadically when engine is speeded up, so must be plugged between the housings and the water tube,any suggestions as how to clean that out?
Expert:  Charles replied 1 year ago.

With no water coming from either side, I would lean more toward the blockage being in the water tube or in the adapter plate. Lets start simple first. Remove the gear case again. Get a good strong flashlight and look up the water tube, Make sure that there is nothing blocking it. There is a ridge on the water tube that needs to be on the upper end, and not the lower. It is easy to get reversed if the tube has ever come out of the engine while doing a water pump.

When you look into the water tube, make sure that you cannot see any rubber from a grommet on the upper end.

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