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Honda BF150 Overheat mystery

C

cgoodwin

New member
Honda BF150 BAPJ-1401310
33' Center console dive boat (commercial)
Motor runs fine until between 3800 and 4500 rpm depending on load, then the overheat alarm comes on and the power cuts, cycling the ignition kills the alarm but when you reach the same rpm it will happen again (Alarm RPM depends on load in the boat)
Running Dr.H I find that the alarm is from sensor #3 (1&2 are on the thermostat housing, 3 is on the exhaust manifold below the 02 sensor, 4 is on the engine block)
I monitored the sensor and it appears that the sensor is showing overheat.
Work performed:
Swapped ECU no change
Replace sensor 1,2&3 no change
Replace water pump impeller no change
Check wiring between sensor 3 and ECU good
replace thermostats no change
Remove thermostats and flush with block with hose no change
Remove water bypass valve and clean, no change
Put motor in a barrel filled with 20% solution of CLR and run motor until hot, then flush with water and repeat 4 times. No change

Any suggestions welcome. I found a thread where someone replaced the seal at the top of the tube connecting the water pump to the engine and solved a mystery overheat - I guess I could look at that...
 
Hi,
I have no experience with this outboard so just tossing out an idea.

Since I often read about some overheats being caused by sand or other debris getting trapped internally inside cylinder blocks, it made me think that it might also happen inside the exhaust manifold.

I see that your manifold has two anodes that are under covers. Items 1,3 and 15 in the link.


Just wondering if removing those covers might open up a flushing path for that manifold?

I also agree with checking the water grommet if you can't find anything else.

Hope you find it.

Good luck.
 
Did you replace only the impeller on the water pump? I did that on my 1999 130 and it still overheated, I needed the full water pump kit with the stainless housing.
 
Great suggestion from NSDON!

A worn impeller liner (cup) or a housing that allows the liner to move/rock and not be held firmly in place will drastically lower the pump's efficiency in many cases. Any wear pattern in the liner will almost instantaneously transfer that wear to a new impeller and can even cause more damage on start up.
 
jgmo said:
Great suggestion from NSDON!

A worn impeller liner (cup) or a housing that allows the liner to move/rock and not be held firmly in place will drastically lower the pump's efficiency in many cases. Any wear pattern in the liner will almost instantaneously transfer that wear to a new impeller and can even cause more damage on start up.
Click to expand...
Good point I will replace the unit
 
See you inspected and clean the water bypass valve but did not replace it. Possibly the bypass valve spring is weak?
 
Run engine til engine warm thermostats open in water or on muffs and check if water is flowing out the thermostat housing by disconnecting the black tube that goes to the exhaust manifold. If no water or limited flow your not getting enough cooling water to the exhaust.
When you drop the lower unit to do the water pump plate and cup, stick a garden hose on the water pipe, I use a vinyl hose with a garden hose fitting on the end and slide it over the water pipe for a snug fit no leaks. Fill the engine with water engine not running and see if water comes out thermostat holes. If water doesn't come up the thermostats means water is not filling engine block and it's leaking out faster than it can be supplied with water. This could be caused by bypass seal, water tube grommet 19252-ZW1-000 on the oil case, or corroded drainage hole on engine block casing?

After you install the new water pump kit, use muffs run engine til warm and see if water will come out the black tube on the thermostat and see how fast it overheats on muffs out of the water. If it overheats at idle fairly quickly it's because when engine is down in the water, the water going into the engine and draining out has resistance from the water the engine is sitting in holding it back into the engine allowing it to get to 4000 rpms before overheating.
 
There are no cooling passageways from the head to the exhaust manifold on the 150. So acid flushing to get that sensor to stop over heating wont work. The cooling chamber in the exhaust manifold is filled from either the small black tubes off the pressure relief valve or up from the bottom slit where water comes in from the large black tube off the thermostat housing. So if water is not going thru either of those hoses check to see if there is a clog in the small hoses from pressure relief housing up to the fill point between exhaust temp sensor and 02 sensor.
 
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