Yamaha 2.5 cooling blockage

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Ardenfour

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Yesterday using my Yamaha 2.5 4 stroke on a freshwater loch we hit lots of algae in shallow water. This seems to have clogged the water intake and was not noticed until the power dropped accompanied by much steam from exhaust. I've cleared the intake holes at the gearbox and now running in a tank there is a strong flow from the yelltale when cold. However as the engine heats up the tell tale falters then stops altogether. Am I correct in thinking there is a thermostat opening and the diverted water is now encountering further blockage? Would this cause the tell tale stream to stop at higher temperature? I had the manuals but they don't really help much, just say 'clear water passages'
 
My Suzuki 2.5 has a thermostat so your Yamaha probably does as well. It definitely sounds like a blockage in that area. I wonder whether you could try reverse flushing with a hosepipe through the tell-tale and exhaust outlets. Remove the spark plug before you start the engine and check there is no water in the cylinder before starting up after the back-flushing.

However, the problem is still going to be the closed thermostat I guess, so a partial strip down might be inevitable I'm afraid. :(

Richard
 
Ardenfour said:
Yesterday using my Yamaha 2.5 4 stroke on a freshwater loch we hit lots of algae in shallow water. This seems to have clogged the water intake and was not noticed until the power dropped accompanied by much steam from exhaust. I've cleared the intake holes at the gearbox and now running in a tank there is a strong flow from the yelltale when cold. However as the engine heats up the tell tale falters then stops altogether. Am I correct in thinking there is a thermostat opening and the diverted water is now encountering further blockage? Would this cause the tell tale stream to stop at higher temperature? I had the manuals but they don't really help much, just say 'clear water passages'
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Yes it has a thermostat ( Under the same cover on top of the engine that you remove to access the anode ....... see http://www.boats.net/parts/search/Y...Later/F2.5MSH/CYLINDER CRANKCASE 1/parts.html )

There should be a flow from the telltale at all times but I suspect there is a partial blockage between the pump and the powerhead, There is sufficient water getting through to maintain the flow from the telltale when the thermostat is closed but that when it opens to allow water to flow through the main parts of the engine cooling system there is insufficient to maintain the telltale flow.

You could try as Richard suggests backflushing from the telltale to the inlet but the water pump will tend to limit the effectiveness of this.

I expect you will have to remove the gearcase unit , check/ clean the water pump then the back flushing may be effective or you may have to remove the thermostat clear that area and flush the water tube from the pump to the power head.

Hopefully you will be able to flush it clear without removing the powerhead.
 
Before doing any of this you've checked/replaced the impeller that probably died in the heat?
 
Stuartk said:
I cant send water up the feed pipe I take it the stat is blocked. Where is it and how to acccess
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Same engine as in this very old thread which you have resurrected and hijacked ? Its always better to start you own new thread giving full details
Stuartk said:
I would love a tear down manual Does such a thing exist
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There may be a Service Manual available from your Yamaha dealer.
Alternatively there are a couple of Seloc manuals . One covers all Yamaha, Mercury and Mariner 4 stroke engines 2.5 to 225hp from 1995 to 2004 . The other all Yamaha 4 stroke engines 2.5 to 350 hp from 2005 to 2010.
 
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now double checked pump all ok . Dismantled as far as thermosstat- Think its knackwered ordered new and anode in bits Ordered. new- Will advisee when fitted. Theres a. tube cpming out of the stat housing Seems to empty into leg- Does anyone know better ??
 
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