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Honda BF40A overheating

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DSAT04

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Hi, I have a 2006 Honda BF40A that currently has an overheating issue. However, it seems to overheat when in gear and under load 3000rpm and above. I can only get around 50 meters of travel on the water before the red light comes on and the alarm sounds. The engine cuts rpm (as it should) I go to neutral, then within 30 seconds the light goes out, the alarm stops and the engine stops. I can restart immediately, then back into gear load up the rpm, go another 50 meters or so and it all repeats. I have done the following work:
Replaced the impeller, the thermostat, the temperature sensor. I have also removed the water jacket cover and cleaned out the area (it wasn't very dirty or clogged and the anode was still good). I have removed the head, cleaned the water jackets in the head and around the cylinders. I replaced the head gasket, the valve cover gasket and the intake manifold gasket. Still having the same issue. While the water flow out of the tell tale at idle is not what I would call strong it is constant and gets stronger with more rpm. I am about to pull it all apart again to check it all but, thinking that I am chasing my tail a bit. Any help would be greatly appreciated.
 
Hi,

I'm no ex-spurt. Never worked on a 40hp so just offering my opinion/guess based on stuff I've seen on twin models I have worked on.

Your description of the less than desirable tell-tale flow makes me suspect either the water tube alignment/connection or the grommet at the top of that tube. Item 8 in the link below.


See item 12 in the link below for the part number of that grommet:


I've seen those water tubes dislodge where they enter the engine block as well as the grommet tear, split and come apart.

Both conditions will cause much of the water from the pump to not enter the engine for cooling and that also diminishes the water available to the tell-tale bypass possibly causing this symptoms you describe. It's a critical connection point for cooling.

Good luck.
 
jgmo said:
Hi,

I'm no ex-spurt. Never worked on a 40hp so just offering my opinion/guess based on stuff I've seen on twin models I have worked on.

Your description of the less than desirable tell-tale flow makes me suspect either the water tube alignment/connection or the grommet at the top of that tube. Item 8 in the link below.


See item 12 in the link below for the part number of that grommet:


I've seen those water tubes dislodge where they enter the engine block as well as the grommet tear, split and come apart.

Both conditions will cause much of the water from the pump to not enter the engine for cooling and that also diminishes the water available to the tell-tale bypass possibly causing this symptoms you describe. It's a critical connection point for cooling.

Good luck.
Click to expand...
Thanks for the advice, I will be having a look at the water tube.
 
Hi all,

I pulled the bottom end off of the leg yesterday in preparation for the new water pump parts arriving. On closer inspection of the impeller and housing...the impeller looks ok but the housing appears to be scorched and melted in places around the edge of the cup and inside the centre hole. Also, the centre hole of the cup has damage, it appears to be more of an oblong shape than a circle. There is also a raised edge around half of the circumference on the centre hole of the cup, where the impeller contacts it. Has anyone seen this before? Does anyone think this would be causing the overheating issue? I am thinking it would certainly be contributing but possibly not the sole reason.
 
Yes, definitely will be part of the problem. It probably "dry started" a time or two. It only takes seconds with no water for lubrication to burn one up because it didn’t self prime correctly. Once it's damaged, it won't prime properly afterward.

But follow through with inspecting the other areas discussed and the vinegar flush. They just don't run forever without maintenance.

Although, I must say, you own one of the best, most rugged, 2 cylinder outboards ever made.

I maintained a fleet of BF8D's in rentals for several years. Compared to other outboards we also rented, the 8D was far and away the MOST reliable and rugged of them all.

I call that BFD series (8D, 9.9D, 15D and 20D) the LIFETIME series because that's how long they will serve if properly maintained.
Nothing but quality those!
 
In case you don't already know, make sure that you use marine grease during assembly so that first prime goes "smoothly" at startup.

I suggested doing the vinegar flush prior to disassembly because, if you do it after installing the new pump, you will likely be dissolving and washing away your assembly lube prematurely. No, it doesn't stay in there forever anyway but the longer the grease is in there before being washed away, the better.

Never crank the engine unless the water intake screens are correctly submerged or are covered with muffs already flowing water. Although I don't like muffs and pretty much stopped using them years ago, I realize many people do. Flushing and test running in a tank is a superior technique for several reasons in my opinion.

Good luck.
 
jgmo said:
In case you don't already know, make sure that you use marine grease during assembly so that first prime goes "smoothly" at startup.

I suggested doing the vinegar flush prior to disassembly because, if you do it after installing the new pump, you will likely be dissolving and washing away your assembly lube prematurely. No, it doesn't stay in there forever anyway but the longer the grease is in there before being washed away, the better.

Never crank the engine unless the water intake screens are correctly submerged or are covered with muffs already flowing water. Although I don't like muffs and pretty much stopped using them years ago, I realize many people do. Flushing and test running in a tank is a superior technique for several reasons in my opinion.

Good luck.
Click to expand...
Thanks mate for your support and advice. I have made a tank out of a rubbish bin. As you say, far superior way of flushing. While I have the bottom end off, I will back flush the system. I have checked the water tube for looseness or if it is out of alignment, it is good no issues there. Just waiting for the parts to arrive then I will reassemble. I will make sure to apply some marine grease during assembly.
 
As the engine only goes into overheating mode while in gear and under load. Is it safe to load it up while it is in the flushing tank?
 
As the engine only goes into overheating mode while in gear and under load. Is it safe to load it up while it is in the flushing tank?

Picture of the damage to the cup and housing
 

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I assume I’m seeing damage to your plastic housing, did you order that part.

I can’t advise on running the prop in a barrel, I wouldn’t do it but maybe someone else has. I’m not sure it would even be a good test of “load”.

Looking at that picture, I’d say getting those parts replaced will make a big difference in cooling.
 
DSAT04 said:
As the engine only goes into overheating mode while in gear and under load. Is it safe to load it up while it is in the flushing tank?
Click to expand...
I’ve put my Suzuki 90hp in gear to check shifting in F and R momentarily. You loose a lot of water fast. I was nervous of what the turbulence would do to the ability of the intake/pump to pickup water. If you took the prop off then it would be less turbulence and I would THINK it would be safe to increase the revs. Watch the barrel water temperature, it will climb fast.
 
NSDON said:
I assume I’m seeing damage to your plastic housing, did you order that part.

I can’t advise on running the prop in a barrel, I wouldn’t do it but maybe someone else has. I’m not sure it would even be a good test of “load”.

Looking at that picture, I’d say getting those parts replaced will make a big difference in cooling.
Click to expand...
Yes, the heat damage to the housing is hard to see in the photo. The damage to the centre hole of the cup is easier to see. I don't think I will try and load it up while in the flushing bin. I will only check the water flow, then take it down to the boat ramp (it's only a 5 minute drive away) to test under load. Thanks for advice.
 
William01 said:
I’ve put my Suzuki 90hp in gear to check shifting in F and R momentarily. You loose a lot of water fast. I was nervous of what the turbulence would do to the ability of the intake/pump to pickup water. If you took the prop off then it would be less turbulence and I would THINK it would be safe to increase the revs. Watch the barrel water temperature, it will climb fast.
Click to expand...
Thanks for the advice. I think I will only check the water flow while it's in the flushing tank. I will put the boat in the water to put it under load.
 
I back flushed the engine, no issues there. Water pump parts arrived. I have fitted them and put the bottom end back together. Tested in a flushing tank, the tell tale was stronger. I will put the boat in the water and see how it goes. I am hopeful but not confident that the overheating issue is fixed.
 
Hi All, good news... I have fixed the overheating issue. I just come home from an hour long test run of the engine. The engine ran constantly at 4500 - 5000rpm and no alarms. Tell tale was constant. I even took it to WOT (6000rpm) briefly and no alarm. I believe that the issue turned out to be a water pressure problem. I think the old impeller cup and housing damage was causing the pump to loose pressure. As NSDON suggested I replaced the whole water pump instead of just the impeller. This has done the trick. Thanks again to all for the advice. A good outcome. 👍😃
 
I learned about how fussy the water pump system is on Hondas by replacing only the impeller on mine. Even though the stainless housing looked very good, it needed replacing. Glad that’s all that was wrong with yours.

Someone on here gave me this good advice. 👍👍
 
Hi All, thank you for your help with the overheating issue. Now that the overheating issue is fixed I have another issue...
With two people and some fishing gear, cruising at 5000rpm (according the tachometer) the boat is only doing 15kmh per hour. WOT 6000rpm, the boat only reaches 19-20 kmh per hour. Specifications on the engine give a top speed at WOT of 44 kmh. Going by my speeds, I am around half of what it should be.
 
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