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Honda BF40A with cooling issues

O

olabri

New member
Have bought a preowned Honda BF40A that gets hot when you drive high speed and then slacks off. After slacking off it takes a few seconds before the alarm goes off, and there is quite a bit of exhaust (white). It also heatens when running at high speed, but that seems to take longer, that can be a coincidence.

When it's running high speed, the cooler water is coming out cold and fine, when slacking off it goes hot as well.
I know that the previous owner has had trouble with the cooling, with running it dry so the impellar smoldered to bits and clogged the coolant lines. This should now be alright, being cleaned up in an authorized workshop.
Can it be some lines are still clogged?

Anyone who has any troubleshooting tips?



 
The tell tale is a separate chamber designed to indicate that the water pump is working. The water from the tell tale has not actually gone through the engine as part of the cooling system. I have a BF30A and after replacing the water pump and servicing the motor the tell tale started to decrease in flow. I attached a 1 gallon garden pump sprayer to the telltale at the pump trigger handle with the wand removed. Pumped it up with just air as much as I could. The motor was in the water and after I shot the air through the telltale in few seconds bubbles started to come out from the lower end. I repeated the process using a dilution of salt away. That was close to last spring and have good telltale flow since. hope this helps
 
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It sounds like it could still have some blockage in the cooling passages. The white exhaust could be an indication that there is debris in the exhaust manifold and it is getting so hot that the coolant being pumped through it is turning to steam. Almost all marine engines, including most outboards, have water cooled exhaust.

Another possibility would be that water is entering one or more cylinders and is vaporizing. This can happen because of a bad head gasket or damaged/cracked cylinder head or engine block. Hopefully it's none of those and you just need to get the cooling passages "blown" out.

Pull the spark plugs and see if one or more of them seems really clean at the tips. This is a good check to see if "steam cleaning" has been occurring in the cylinder. If not, and the plugs look "normal", then breathe a sigh of relief and go back to getting the junk out of the cooling passages.

You can do a pretty good job of blowing out the passages with an air compressor. There is no need to worry about the pressure as there is no delicate radiator or heat exchanger to worry about on your outboard. You will need to pull the thermostats and the extension case to do this but I saw no mention of thermostats in your post so they need to be inspected and tested to make sure they aren't part of the problem.

If you're going to do it yourself you will need an air blow gun with a rubber tipped nozzle to blow into the tell tale in the block. You can make a decent seal with a rag or old tee shirt when you try to backflush through the t-stat passages.

Good luck and ask all the questions you want.
 
Well, I would still pull the spark plugs and see any have a really clean look. But blowing out the cooling system might be what she needs.

Good luck.
 
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