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Honda BF25 Outboard Cooling question

DGR

New member
I have a Honda 25 hp outboard that I have had for a couple of years (bought used). Since I've had this outboard the coolant stream from the motor has always been flowing whenever the motor has been on.

The last time out I had some problems with keeping the engine RPMs up for an extended period of time. After a couple of minutes of higher speed operation it would start to cut out. I could idle it awhile and then it would be able to run a higher speeds for a short time before starting to cut out. I think that problem can be attributed to fuel tank venting (or non-venting). Anyway, by the end of several minutes of working that problem I noticed the coolant stream having intermittent flow. This was on the way back to the ramp.

Back at the house, while running it in a bucket of water, I tried some wire up the coolant outlet tube to check for blockage - no change. Only getting a drip out the coolant tube at this time.


So I go look at the thermostat. It had a good coating of scale and dirt and corrosion. I soaked it in some CLR and it cleaned up pretty good. I then tried the hot water test on the stove. I started with the water cool and took it up to boiling while the thermostat was in the pan - I noticed no change. I thought I should see it change position. So I ordered a new thermostat. The elements of the new thermostat were in a different position than the old one.


Next I look at the impeller. It looked OK but it has a few years on it and I figured since the boat is down I'd change that too to take that out of the question.


I put it all back together and start it up but no change. Still just a drip out of the coolant tube.


Any help out there on what I am seeing? First do I have a problem? As the thermostat cycles does it change the coolant flow out of the engine. Should there always be coolant flow out of the engine or does it depend on the thermostat position? What should I check next?

Thanks in advance,

Doug
 
The coolant stream is not controlled by the thermostat. It originates before the water goes up to the thermostat. Generally, the things that affect the stream are intake and water pump condition; sealed water passages (no leaking gaskets internally); and lastly and most common..blockage in the system.

First...make sure that the water level in your bucket goes almost 1/2 way up the engine. The water pump must be entirely covered...not just the intakes (all three).

It does sound like the thermostat may have been causing your run-ability issues. It may have been overheating and running in safe mode. If that was the case, there should have been an alarm. Although some tiller versions, do not have an audible or visual alarm.

If you have access to compressed air, next time you have the motor in the bucket, blow back up through the indicator hole until you see bubbles coming out the bottom of the motor.

The thermostat should fully open around 180 deg. So boiling water should do it.

You said the elements appeared different in the new thermostat. Make sure the new thermostat temperature matches the one on the old one. It is engraved in the small end of the thermostat in centigrade.

Mike
 
Not sure which 25 you have so I just picked a 2000 for the parts page link below. We just had a guy post here a week ago or so with the same sort of issue with his pee stream. I think he said that he enlarged the holes in items #4 and #17 in the link below to get a good, reliable stream.

http://www.boats.net/parts/search/Honda/Outboard Engine/1999/BF25AX LRSA /ENGINE COVER/parts.html

Also, if your hose between the two is not VERY SOFT and pliable, get some new at the auto parts store. I change that hose out pretty routinely.

Debris pumped in from the intake screens can get a good foothold in the coolant passages. Luckily for most of us, they all pretty much migrate to the water check passage where they can be removed. I have a particular problem of tiny little "twigs" that get through on my rental fleet that is located in a desert setting. I think they come from tumble weeds. They are the perfect size to get through the screens and lodge just inside the engine prior to getting to the #4 fitting. Pushing from the outside in with a wire does not usually work. I have to take the fittings off and dig out the twigs and then run the engines without the fittings installed to flush anything that was behind the twigs. Enlarging the passages in the fittings, if you can, is a good idea.

Good luck and I hope the compressed air thing Mike told you about works. It is the easiest method by far.
 
Just found this thread and have the same problem. Have blown out pee hose without luck, Seems like I should just remove the possibly collapsed hose between 4 and 17 to see if water flows at all before I consider finding the water pump.
Agreed?

Gene Porter

Not sure which 25 you have so I just picked a 2000 for the parts page link below. We just had a guy post here a week ago or so with the same sort of issue with his pee stream. I think he said that he enlarged the holes in items #4 and #17 in the link below to get a good, reliable stream.

http://www.boats.net/parts/search/Honda/Outboard Engine/1999/BF25AX LRSA /ENGINE COVER/parts.html

Also, if your hose between the two is not VERY SOFT and pliable, get some new at the auto parts store. I change that hose out pretty routinely.

Debris pumped in from the intake screens can get a good foothold in the coolant passages. Luckily for most of us, they all pretty much migrate to the water check passage where they can be removed. I have a particular problem of tiny little "twigs" that get through on my rental fleet that is located in a desert setting. I think they come from tumble weeds. They are the perfect size to get through the screens and lodge just inside the engine prior to getting to the #4 fitting. Pushing from the outside in with a wire does not usually work. I have to take the fittings off and dig out the twigs and then run the engines without the fittings installed to flush anything that was behind the twigs. Enlarging the passages in the fittings, if you can, is a good idea.

Good luck and I hope the compressed air thing Mike told you about works. It is the easiest method by far.
 
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