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Old 05-23-2004, 09:19 PM
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Default Yamaha OX 66 Pressure Relief (poppet) Valve

Andy:

Replacing thermostats on my 2002 Ox 66 and the Yami manual suggests checking the pressure relief valve also. this brings me to my question. What is the function of this valve, what pressure is it supposed to relieve. how do you know if it is functioning properly? Is frequent blowing of exhaust and water from the vent aft and below the lower cowling a sign of a problem? I don't recall this happening before.
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Old 05-24-2004, 11:19 AM
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SIM
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Default RE: Yamaha OX 66 Pressure Relief (poppet) Valve

george,

The purpose of the popit or pressure relief valve is to let the cooling system build water pressure up*to keep the system under pressure. If the valve is stuck open(weak spring, crude on the valve seat) the water will not reach the upper parts of the engine since its being dumped out the open valve. Usually a indication of this happening is the engine overheat warning goes off at low engine speeds even though there is a good stream coming out of the engine. The reason is... the valve being open and the cooling water level in the upper part of the engine is not high enough. This is were the overheat sensor is located and if does not have water around it, it activates

Andy
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Old 05-25-2004, 08:59 PM
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Default RE: Yamaha OX 66 Pressure Relief (poppet) Valve

Andy

Thanks for the explanation! Mine appears to open intermittantly, no overheat or alarm warning. Will check the valve out when I replace the T-stats. Seems to be a little difficult to access, tucked under the ECM below the top of the lower casing on the 250 HP OX 66. Any tips on how to get at it more easily? Also, sucked a lot of mud into the cooling system recently. Might have gummed up the valve and the T-stats.
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Old 05-26-2004, 09:42 AM
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Default RE: Yamaha OX 66 Pressure Relief (poppet) Valve

Cant offer any advice on how to make the job easier. I dont have any of those engines around to get a look at.

You possibly could have some debris in there hanging up the valve or the spring is getting weak.

Andy
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