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  #1 (permalink)  
Old 09-30-2012
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Join Date: Aug 2012
Posts: 10
Default Engine temp alarm

Yamaha 200hp 2stroke. (200FETO 6G6 X 507697 U)

Problem - the Alarm for high temp sounds at about 3300rpm after 5 min running time and the engine cuts back on RPM. couple minutes in idle and were away again, this will repeat all day long. If I run the boat on lower RPM does not set the alarm off. If i run much faster the the time between alarms is much shorter. No indicator on the gauge when the alarm goes!! I have tested this by shorting the wiring at the motor and the beeper goes but no indication on the gauge. Im picking the "thermometer" on the gauge is for the Temperature sensor on the engine, not the switches near the thermostats

I have taken off the on/off switches on both heads and tested on a stove, both the switches operate same, trip at 87Deg and reset at 75Deg.

I have taken the temperate sensor off and tested that in cold water through to hot water and that too is working to the spec in the repair manual.

I have changed both the Thermostats 2 months ago and the water pump impellor. still had problems so i took it to a marine shop who also swapped the water pump housing. but it does not change the way the temp alarm operates.

I did a compression check and it did not indicate an obvious problem. The mechanic did indicate that the bottom crankcase seal is staring to pass as some fuel was running down the shaft. but nothing that should set off the temp alarm.

I also tested the level switches in the small oil tank on the motor and the larger tank on the boat. these worked fine too. Im thinking a blockage in the water system somewhere? or a gasket problem that becomes a problem at higher RPM?

Carbs were cleaned couple weeks back by the mechanic too, and spark plugs.

Im a bit stuck, the local mechanics have a very high rate and i would rather fault find myself and let them repair the problems rather than spending lots of time trying to find the problem.
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Old 10-01-2012
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Join Date: Jun 2012
Location: Pensacola
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I see no where in the story the pressure control valve has been serviced,, if you are alarming at mid range or higher this is most likley the issue,, it is stuck closed..
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Old 10-01-2012
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Join Date: Dec 1969
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My thoughts are cooling passages plugging up, might monitor the temperature of heads with a infra-red gun to make sure it is overheat problem and which one is overheating.
How did the passages around stats look when you had them out?

I do not understand how a PRV stuck closed would cause an overheat as it just relieves overpressure at higher RPMs
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Old 10-02-2012
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Join Date: Aug 2012
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thanks for the feedback guys, I did have a look at the "poppet" valve, its a fairly simple item, stainless spring pushing a plastic plug onto a seat. All looked in order so i put it back.
I have had a infra red temp unit on the last run on the boat and did shoots for temps both heads, but i did not notice one "hotter" than the other but for a couple of degrees. Ive got a feeling that there could be a blockage somewhere, any idea's where i would find a drawing of the cooling water circuit, especially how the Poppet valve works in the system and places to check if there could be blockage

when i replaced the thermostats there was some build up of white powder but not, i have attched a pic.

I have read a comment in another forum that a cooling passage eas blocked underneath the temp sensor location. the problem with that engine went away after cleaning, i would like to know if this applies to my engine before pulling heads of etc.
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Old 10-02-2012
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Join Date: Jun 2012
Location: Pensacola
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Quote:
Originally Posted by 99yam40 View Post

I do not understand how a PRV stuck closed would cause an overheat as it just relieves overpressure at higher RPMs
We see it all the time here in our salt water enviroment,, the engine cannot get enough water flow through the thermostats at highter rpm,,,
stuck closed over heat at higher rpm,
stuck open over heat at idle...
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  #6 (permalink)  
Old 10-02-2012
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Join Date: Aug 2012
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thanks for the info. i will check today and get a new PRV anycase.
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