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Honda BF8D overheating (maybe?)

P

Pells

New member
Hi, I'm new to marineengine, hope someone can help me out. I have seen this problem described in several other forums; however, no one has reported a fix. I have a Honda outboard model # BF8D-BAAJ-1802157. I am the original owner, purchased about 10 years ago. It is used infrequently to move my 23' sailboat from the marina ramp to clear air. Honestly have less than 20 hours on it. I maintain and winterize the engine every year. About four years ago, the engine started stalling after running perfectly fine for no apparent reason. It always restarts easily and continues to run perfectly again. Every year the frequency of stalls increases. Now it only runs for one or two minutes. I have cleaned, inspected, and replaced everything fuel-related, yielding zero improvement. I read in the manual that the engine will reduce rpm and shut down if overheating (no indicating light - thanks Honda). The coolant stream (pee) is steady and strong. Inspected, tested, and replaced both the thermostat and temperature sensor. No change, engine runs for a minute or two, then dies. I removed the temperature sensor, and water gushes out of the open port while running. Makes me believe the water pump is OK. Reinstalled the temperature sensor to plug the hole, but connected the spare connector (now sensing ambient air temp), and the engine runs fine (no stalling), but the head seems to get hot. I measured 200F near the spark plug after a few minutes. There is a little bit of corrosion in the thermostat cavity, but not a significant buildup. Can there be a blockage in the coolant path somewhere? How could you find a blockage without disassembling the entire engine? BTW engine oil is OK. Does anybody have a suggestion before I trash this outboard?
 
Hi,
A waterpump with missing impeller arms will  Still move a good deal of water and fool you into thinking that the pump is ok. Also, if the impeller arms are broken off, they can work their way up into the engine block and, yes, block some coolant flow.

Based on what you're saying, I would pull the pump and inspect/replace. 10 years for a pump is a very long time.

With the pump off, you can try backflushing/downflushing the block with the thermostat removed.
You might also consider removing the water jacket cover to inspect in there and replace the sacrificial anode and mount screw. See items 1, 8, 9, and 12 in link below.


While, at first, some pump components may still look serviceable, very close inspection will usually reveal wear of the liner inner surface (the "cup" that the impeller sits in and wipes against) as well as some play between the cup and housing. The surface of the "cover" (item 5 in the link below) may also show some wear that looks "minor" but even a small amount of wear or looseness will greatly affect pump efficiency and life. This applies right down to the drive key. I would recommend an entire pump kit (item 2) as opposed to just a new impeller. Much more expensive, yes, but will return the cost over time in efficiency and longevity.


Lastly, it might be a good idea to run this outboard in a tank (trashcan) of vinegar solution to help remove/reduce deposits inside the system prior to disassembly. Just keep a VERY close watch on both head and supply water temperature. Especially if you do it with the temp sensor removed.

While Honda didn't supply a warning lamp with all models, the EPP (engine protection program) built into the CDI module has already prevented damage from occurring so don't be too upset with them.

Good luck.
 
My post regarding a 5hp sounds like it was being how your outboard is being used- infrequently. The thermostat was plugged and lot of salt crystals in there.

I ran the 5 hp a barrel in vinegar and water yesterday, without a thermostat installed for 20-30 minutes. Using an ir gun on the top of the thermostat housing, it got up around 80f iirc. Drained vinegar water and refilled the barrel with fresh water and with the thermostat installed, the housing would show 120-125F, which is the range for the thermostat to open and close. If your new thermostat opens and closes like that, your cooling system is likely clear?

Infrequent use is bad for these small outboards in both cooling systems and fuel systems. They really don’t get hot enough when used little to keep the cooling system cleaned out and also typically don’t get flushed with fresh water.

The fuel system needs close attention, fresh ethanol free 91 or higher octane and nice clean fuel is needed, plus if possible, nice long hot runs to keep varnish from appearing in the carb jets etc. I’d recommend using a dose of Sea Foam in every tank of fuel to keep it cleaned out. It also eliminates water from ethanol or from water in the tank.

JGMO is the pro on these small carbs and the process to follow to clean them properly once they have been varnished up from lack of use etc.
 
NSDON said:
My post regarding a 5hp sounds like it was being how your outboard is being used- infrequently. The thermostat was plugged and lot of salt crystals in there.

I ran the 5 hp a barrel in vinegar and water yesterday, without a thermostat installed for 20-30 minutes. Using an ir gun on the top of the thermostat housing, it got up around 80f iirc. Drained vinegar water and refilled the barrel with fresh water and with the thermostat installed, the housing would show 120-125F, which is the range for the thermostat to open and close. If your new thermostat opens and closes like that, your cooling system is likely clear?

Infrequent use is bad for these small outboards in both cooling systems and fuel systems. They really don’t get hot enough when used little to keep the cooling system cleaned out and also typically don’t get flushed with fresh water.

The fuel system needs close attention, fresh ethanol free 91 or higher octane and nice clean fuel is needed, plus if possible, nice long hot runs to keep varnish from appearing in the carb jets etc. I’d recommend using a dose of Sea Foam in every tank of fuel to keep it cleaned out. It also eliminates water from ethanol or from water in the tank.

JGMO is the pro on these small carbs and the process to follow to clean them properly once they have been varnished up from lack of use etc.
Click to expand...
Can you recommend a water vinegar ratio? Perhaps 10:1 or 20:1? I assume this will help dissolve some deposits/ buildup? Thanks, -Ken
 
Ordinary white vinegar is 5% acetic acid , I used 8 liters in my blue barrel and filled it up to about 3 inches above the anti cavition. 2 -4 liter jugs. I’ve used 4 jugs in my 130 hp with a full barrel.

This barrel was about half full at most, I’d say 75-90 liters.
IMG_1987.jpeg
IMG_1987.jpeg
 
jgmo said:
Hi,
A waterpump with missing impeller arms will  Still move a good deal of water and fool you into thinking that the pump is ok. Also, if the impeller arms are broken off, they can work their way up into the engine block and, yes, block some coolant flow.

Based on what you're saying, I would pull the pump and inspect/replace. 10 years for a pump is a very long time.

With the pump off, you can try backflushing/downflushing the block with the thermostat removed.
You might also consider removing the water jacket cover to inspect in there and replace the sacrificial anode and mount screw. See items 1, 8, 9, and 12 in link below.


While, at first, some pump components may still look serviceable, very close inspection will usually reveal wear of the liner inner surface (the "cup" that the impeller sits in and wipes against) as well as some play between the cup and housing. The surface of the "cover" (item 5 in the link below) may also show some wear that looks "minor" but even a small amount of wear or looseness will greatly affect pump efficiency and life. This applies right down to the drive key. I would recommend an entire pump kit (item 2) as opposed to just a new impeller. Much more expensive, yes, but will return the cost over time in efficiency and longevity.


Lastly, it might be a good idea to run this outboard in a tank (trashcan) of vinegar solution to help remove/reduce deposits inside the system prior to disassembly. Just keep a VERY close watch on both head and supply water temperature. Especially if you do it with the temp sensor removed.

While Honda didn't supply a warning lamp with all models, the EPP (engine protection program) built into the CDI module has already prevented damage from occurring so don't be too upset with them.

Good luck.
Click to expand...
I installed a water pump kit. The old impeller looks OK; it has all the arms and is flexible. Replaced the impeller anyway. Same problem, the engine runs smoothly from cold start until the block measures 180°F (next to the temperature sensor). Then it shuts down, like it is running on one cylinder for 10 seconds, then it stops. The pee stream is cool while the engine is running, but after the engine dies, the dribbling pee stream turns hot. This is very weird. I can't figure this out.
 
Hi Pells,

Sorry this is happening to you. A REAL PAIN I know!

Ignore the tell-tale water getting hot as soon as the engine stops. That is normal.

It happens because the water you feel while the engine is running is coming UP from the pump and supply tank or whatever water you're operating on.

The water you feel after stopping the engine is water that has been up inside the engine and has absorbed heat from the metal but is now coming back DOWN, out of the engine due to gravity because the pump has stopped pushing the water upward.

It's actually pretty amazing if you think about it. That water has only been inside the engine for maybe a couple of seconds but has picked up enough heat to actually scald you in some cases. Be very cautious about putting your hand in that stream because of that.

Now, back to the problem.

If I'm understanding you correctly, BOTH the old sensor and the new sensor seem to be detecting overheating and (as intended) stopping the engine.

I know you have replaced it but I would first go back and test the thermostat to be sure it's working properly.


If it is, then I don't think you have much choice about pulling the water jacket cover and examining the passages in there. See item 8 in the link below:


With it removed, you can try to "backflush" into the openings to see if there might be something lodged in there.

It's best to do that with the pump removed so anything dislodged can exit out of the water tube. More work I know and that sucks but it is what it is.
You should probably have items 1, 9 and 12 on hand prior to re-assembly.
The anode and it's mount screw are regular maintenance items and the gasket won't always seal back up if reused.


The BF8D Honda outboard is one of the most rugged, reliable outboards made. I know you're not happy with whatever is going on with it but it is one of the BEST and well worth the effort to figure it out.
I rented a small fleet of those and they survived anything and everything the drunks, rocks and weekend warriors could throw at 'em and then start and make the next day.... again and again and again.
DON'T GIVE UP!

And please let us know what you find.
 
Just thought of something else.

Pull off the exhaust chamber cover and make sure there's nothing like a critters nest or weeds in there. If the exhaust water can't easily exit, the head could get hot quickly.
See link.


You can often reuse the big gasket but also make one with stock material from the auto parts store.

!!!DO NOT!!! try pushing water back into the head from the exhaust or there's a danger of water getting inside the engine!!

Check the engine for water intrusion anyway by pulling the spark plugs, pulling it over a couple of times.and checking the oil.

Good luck.
 
jgmo said:
Hi Pells,

Sorry this is happening to you. A REAL PAIN I know!

Ignore the tell-tale water getting hot as soon as the engine stops. That is normal.

It happens because the water you feel while the engine is running is coming UP from the pump and supply tank or whatever water you're operating on.

The water you feel after stopping the engine is water that has been up inside the engine and has absorbed heat from the metal but is now coming back DOWN, out of the engine due to gravity because the pump has stopped pushing the water upward.

It's actually pretty amazing if you think about it. That water has only been inside the engine for maybe a couple of seconds but has picked up enough heat to actually scald you in some cases. Be very cautious about putting your hand in that stream because of that.

Now, back to the problem.

If I'm understanding you correctly, BOTH the old sensor and the new sensor seem to be detecting overheating and (as intended) stopping the engine.

I know you have replaced it but I would first go back and test the thermostat to be sure it's working properly.


If it is, then I don't think you have much choice about pulling the water jacket cover and examining the passages in there. See item 8 in the link below:


With it removed, you can try to "backflush" into the openings to see if there might be something lodged in there.

It's best to do that with the pump removed so anything dislodged can exit out of the water tube. More work I know and that sucks but it is what it is.
You should probably have items 1, 9 and 12 on hand prior to re-assembly.
The anode and it's mount screw are regular maintenance items and the gasket won't always seal back up if reused.


The BF8D Honda outboard is one of the most rugged, reliable outboards made. I know you're not happy with whatever is going on with it but it is one of the BEST and well worth the effort to figure it out.
I rented a small fleet of those and they survived anything and everything the drunks, rocks and weekend warriors could throw at 'em and then start and make the next day.... again and again and again.
DON'T GIVE UP!

And please let us know what you find.
Click to expand...
IMG_9315.JPG
IMG_9316.JPG

I found a blockage at the bottom of the water jacket where the anode should be. It appears that one or two passages to the bottom cylinder were blocked. It cleaned up easily, and the ports seem to be clear. Broke the head off one bolt:). Ordered anode, bolts, & gasket. I'll put it together and try again. Thanks for your guidance, hope this is the root cause. I wonder what the stuff is? Feels like packed salty sand/grit. Probably my bad for not flushing often enough or long enough.
 
Yep, good going! Way to follow through and stay ON IT!

That "gunk" is, in many ways, like a furry critter that likes warm, dark places to curl up and take a forever nap.
Sorta reminds me of my cat.

It seems you found it before it's had a chance to solidify and become "one" with the aluminum.
That's a GOOD thing because there could be more in places that you can't see.

Doing some serious time running it in the vinegar solution after you put it back together is recommended. Just keep a close eye on the water temperature in the tank when doing that. You want to avoid overheating even if the protection program works like it should.

Since the water exits through the lower case and prop hub, you will probably be catching stuff that breaks up and will be able to examine it in the bottom of the tank if you drain the water out carefully.

A siphon hose placed about 1" above the tank bottom helps with doing that efficiently.

I hope this ends up with a sweet running 8D back in your possession.
 
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