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F115 Yamaha 4 Stroke Water not circulating 2005

R

Ricor

New member
Strange situation. Just changed the water pumps about a month ago, tested both and they ran great with strong water coming out the indicators.

Changed a fuel pressure regulator on the starboard motor yesterday and tested the engine and there was no water coming out. Just a couple drips. Waited about 3 minutes to see if the thermostat needed to open, but no joy. The engine sits in a 100 gallon drum for water.

Then tried the Yamaha Flush System, nothing, just drips. It has always flushed in the past with no issues.

Then left the Yamaha Flush system open, and started the engine, nothing. Water usually flows out of the flush input heavily when the engine is started in water. (Yes, never do this!)

Then I removed the lower unit and connected a hose directly to the input shaft that usually goes into the water pump. Water went into the engine, then stopped. A couple drips, out of the pisser but nothing else. When I removed the hose water rushed back out through the input tube like it is blocked.

So it can't be the water pump, for sure. Yamaha flush has stopped working. Water does not circulate when applied directly to the water pump input shaft.

These are great motors in great shape and very well cared for with about 600 hours. Salt water used but always flushed with salt away after every use.

The only things I can think of are 1) The Yamaha Flush system has been left open. A bug big enough to plug the whole system??? 2) Thermostat? But don't they always have bypass?

Any ideas are appreciated. Thanks
 
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Can't be the thermostat - the thermostat will always be closed when you initially start the engine until it reaches correct operating temperature - then it will open and close as necessary to maintain optimal operating temp but you never notice it as all water will bypass all the cylinder head and flow through though bypass coming out the propeller hub and the "pee hole".

Seems as though something is clogged up in there. I'd try pulling out the thermostat on top and running water from a hose down into the thermostat port/opening (maybe stick the hose in there and hold a towel around it to create some pressure). That would force water through from the top down instead of the bottom up. With the lower unit off you couls see chunks, debris, mud (mud wasps) or evidence that something else somehow got up in there or was forced up in there and clogged the flow.

I'll be interested to hear other ideas as this is the first time I've heard of such a thing and I own an F115 with 500 hours on it.
 
So I took the thermostat off, which is 11 years old and looked new somehow, and backflushed the system. I did not see anything come out but it could have. The inside of the block looks good, no flaking or heavy corrosion.

Put the lower unit back on, put it in water and it worked perfectly. Tried the Yamaha Flush System, that worked perfectly too. Go figure. Had to be a mud dobber that got in through the Yamaha Flush System that I left open... That is my only guess.
 
Ricor said:
So I took the thermostat off, which is 11 years old and looked new somehow, and backflushed the system. I did not see anything come out but it could have. The inside of the block looks good, no flaking or heavy corrosion.

Put the lower unit back on, put it in water and it worked perfectly. Tried the Yamaha Flush System, that worked perfectly too. Go figure. Had to be a mud dobber that got in through the Yamaha Flush System that I left open... That is my only guess.
Click to expand...

Glad to hear it is working again. It is strange you didn't see anything come out but who knows - could have been some mud that dissolved with the water or something. 11 year old thermostat? I say change it or at least put it in a small pot of room temp water on the stove and turn on the heat with a thermometer in the water - see that it opens and at what temp. A thermostat that freezes shut or fails can be the death of an engine (the overheat alarm won't tell you it's not opening!). Oil, fuel additives, filters, thermostats and water pump impellers are cheap. New outboards are EXPENSIVE!
 
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