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Honda BF20 overheating

S

Sarrre

Contributing Member
I have a problem with a Honda BF20 with remote control. The overheating buzzer sounds after 10 minutes of idling and the engine shuts down by itself. But the telltale is always nice and strong!

I have changed the thermo switch without any luck. Also the thermostat works fine. Do you have any idea about the problem? It is really driving me crazy!

By the way...if I drive above idle speed before the warning buzzer activates it's no problem. But as soon as I go back to idle speed, the overheating buzzer and lamp is going on after a few minutes!
 
As you have seen, a strong tell-tale does not guarantee adaquate cooling.

Have you replaced impeller and noticed any missing rubber from the old one?

This is often a cause for partial blockage upstream which could cause exactly your issue.

How did it look when you had thermostat out to test? This might be a good location to try some back flush with lower unit open to free flow. Hopefully you won't need to disassemble further to locate and remove blockages.

Do check your impeller while it's open as just a few seconds of dry run can damage or destroy a perfect impeller.

An overly lean mixture could also be responsible for overheating, but would not expect this at idle speed.
Art
 
I agree that this sounds like that there may be a blockage. If there is a chunk of old impeller arm in just right place, it could restrict water flow to the engine and might actually cause more flow through the tell tale bypass. The tell tale is nothing more than a visual check aid to determine that the pump is moving H2O.....it cannot guarantee sufficient cooling. I think Art's suggestion of a good backflush is where I would be going with this one also.
Good luck
 
Glad to have confirmation from a true Honda expert, my Honda Outboard knowledge is limited to my antique workhorse.

Thinking of easiest way to back flush. Certainly open up the feed from the water pump. On my BF-100 this can be done without complete disconnect of shift rod, just clevis pin removal will drop it down a few inches and open water tube connection at pump. Use water, vacuum and air (if compressor available) in that order. Follow with a 'coat-hanger' constructed probe with a little 'hook' bent at the end that can catch pieces up the water tube (they like to stick at top) from pump, Old Speedometer Drive cable works even better.

At the thermostat, BF-100 requires removal of Intake/Exhaust Manifold (two gaskets and many bolts), but there's a bypass hose from thermostat that goes around to near where top of water tube enters block and you might get sufficient flush through that hose. Of course on that engine, you have best access behind thermostat/manifold plates.

Another thought, since problem is seen at idle, but not at higher RPM, would the BF-20 have a "Pressure Relief Valve"? My Yamaha has one next to Thermostat, a round rubber poppet valve inside rubber ring (that can be installed backwards) that has a coil spring holding it closed at low RPM and I can imagine if it did not close, low RPM pump pressure might be too low to cool upper cylinder.

Just dealt with (sediment) blockage in Yamaha which acted the total opposite, (only overheated at high RPM for more than 3 to 10 minutes) and was forced to remove Cylinder Head (and Exhaust Cover) to clear it. No amount of flushing, including extensive high temperature 10% Salt Away in a barrel, helped in the least.
Art
 
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