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Honda 20 HP bf20d overheating

C

Candyorly

New member
Last fall (October) after not running my pontoon for several months, I changed the impeller and tested the motor in a garbage can filled with water. It worked great, strong telltale flow, tested for 60 minutes total across a few sessions. When my wife and I took it to the lake it overheated in five minutes. Unfortunately we cannot recall if the telltale had a stream then or not.

I haven’t had it out since last October. Today, I flushed the engine with the nozzle attachment (no shredded parts or plastic came out) and then disassembled the lower portion and put yet another impeller in, even though the one from the fall looked fine. (When I disassembled it the key fell out but unfortunately I didn’t get a chance to see if it was in the right place initially).

I tested the new one similarly today and I’ll in the bucket it works fine. I fear however that under load it will overheat again. It’s a major pain to get it lake-ready, haul it there and then come home when/if it fails.

I’m wondering what else will make it overheat only under load. I can’t mimic it by running it in gear in the bucket because all the water immediately splashes out. Some say this could be a failed thermostat but I believe I’ve heard that this is almost unheard of with this motor.

Any suggestions appreciated on what could be wrong if anything and what to do next! (If there’s a picture attached kindly ignore it as it’s irrelevant and I’m not familiar with how this forum works with those)
 
Hi,
Sorry you're having problems.
I have a long and loving relationship with the BF20D outboards. They are truly excellent outboards IMO.

There's not alot, other than the waterpump or thermostat that would cause something like this UNLESS there's an internal blockage of some sort OR undue friction in the gear case for some reason. Have you checked the transmission oil level and condition?

I know that, given the same set of circumstances, I would DEFINITELY be suspecting the thermostat.

You could choose to:

1. Replace the thermostat
2. Test the thermostat
3. Run it without the thermostat
to see if the condition improves.

If you choose option 3 and it does improve, DO NOT continue to run the engine without one.

An engine without a Tstat will not run efficiently and will tend to carbon up the valves, rings, pistons and combustion chamber.

Additionally there is also a very real possibility that an engine without a Tstat could actually overheat in high load operation because the bypass "rapid warm up" circuit is always open without a stat.

You can easily overcome water splashing from your testing bucket by removing the prop. It won't load the engine as much but it WILL allow high rpm operation while in gear if you suspect there may be a problem with the transmission having too much friction. It also allows for inspection of the #1 propshaft seal killer....line wrap.

Line wrap not only destroys the seal but can induce load to the engine and transmission.

Removing the prop also allows for inspection/replacement of the thrust washer. If the washer shows ANY wear, replace it.


The key falling out could be nothing or it could be a clue. Inspect it very carefully as well as the slot in the shaft for signs of wear.

Putting a new impeller in an old pump cover and housing often doesn't work well. Look closely at the cover (cup) the impeller wipes in. What looks like a "little wear" will reduce the pump's efficiency by quite a lot and will immediately start wearing the new impeller down at start up.

If there is ANY rotational movement, side to side, of the cover inside the plastic housing, I wouldn't reuse either and would replace with the complete pump assembly Honda sells. Sure, it costs more but will work and will last. A new pump assembly WILL often accept a new impeller after a season or two without much loss of efficiency.

It's a pain but if you remove the right under cover and take the tell-tale fitting out of the block, you can get a very good indication of just how well the pump is working.
On start up, it should prime and push out an unbelievable amount of water almost immediately. So, be ready to shut off quickly.
That's how I usually clear the tell tale of blockage on my 2006 20D.
Just be aware that the screws for Honda are JIS (Japanese Industrial Standard) and NOT Phillips even though they look similar.
Also, the tell-tale hose is routed a very specific way and won't work well or not at all if not installed correctly. It should also be soft, pliable and "limp". Otherwise, it will tend to get blocked by small pieces of stone or twig debris.
I change it out every 3 seasons or so as "regular maintenance"

If the pump is working properly and the tstat is good then you very well could be looking at a blockage. I know that you said you tried clearing the passages but it might require more to dislodge something in there.
Removing the stat gives access to the passages so that you can try reverse flushing. It's ok to use full shop air pressure along with water to try and force things out the bottom with the gearcase removed.

I hope you can sorted this out and will update with what you find.

Good luck.
 
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