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  1. #1

    pro 785 experts needed

    long time user, first time poster. I recently purchased a pro 785. Today, I was out in the garage working on it, and was wondering why the coolant sensor on the head would be cut? Is that the yellow wire from the cdi everyone talks about cutting to gain 200 or so rpm? Next question, by the gas tank, there are two (look like one way valves) that are just dangling. They are not connected to anything. Are they supposed to be connected? I have a picture of what they look like if someone needs one. Thanks for the help.


  2. #2
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    The two valves are the fuel tank vent. One allows air into the tank, the other one allows pressure to build in the tank. Its a check valve that I think allows about 2 PSI to build in the tank. THere should be a hose from that pressure relief valve to a vent on the outside of the ski. I have no idea why the temp sensor wire would be cut. It shouldn't be that way.

  3. #3
    Click avatar for tech links/info, donation request K447's Avatar
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    There are two vacuum relief check valves, one for the oil tank and one for the fuel tank. Each has only one hose connection and the other end hangs in the air.

    The fuel tank also has another check valve with two hoses attached, one from the fuel tank and one to a hull vent fitting.

  4. #4
    I figured they were some sort of vent valve, but wanted some other opinions. As far as the temp sensor, I have no idea why its cut. I am soldering it back tonight. It could have been cut by accident or something. Thank you for the help.

  5. #5
    The temp sensor is cut because they were riding it in cold water and the temp sensor was letting it get too hot and then all of a sudden letting 60 degree water coming through the cylinders cold seases it my 785 and 1200 both had them cut when i purchased them and i havent had a problem with them being cut it doesnt hurt anything. its a little harder to get to operating temp in cold water but thats all.

  6. #6
    Tony's Avatar
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    The sensor only closes a circuit at a certain temp causing the MFD to display "HOT", it doesn't have anything to do with regulating the temperature.

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    Quote Originally Posted by polaris pro 1200 mods View Post
    The temp sensor is cut because they were riding it in cold water and the temp sensor was letting it get too hot and then all of a sudden letting 60 degree water coming through the cylinders cold seases it my 785 and 1200 both had them cut when i purchased them and i havent had a problem with them being cut it doesnt hurt anything. its a little harder to get to operating temp in cold water but thats all.
    I ride in water thats barely above freezing and never had a seizing problem. I run a temp gauge on my ski, and in cold water it will never get to operating temp without the thermostat. It will run up to temperature when idling, but it does cool off when the popoff valve opens. Do you mean removing the thermostat and bypass valve? The sensor is just a switch, it has nothing to do with water flow.

  8. #8
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by polaris pro 1200 mods View Post
    The temp sensor is cut because they were riding it in cold water and the temp sensor was letting it get too hot and then all of a sudden letting 60 degree water coming through the cylinders cold seases it

    my 785 and 1200 both had them cut when i purchased them and i haven't had a problem with them being cut it doesnt hurt anything.

    its a little harder to get to operating temp in cold water but thats all.
    This is not making sense.

    The temp warning sensor has nothing to do with controlling water flow or even controlling engine temperatures. It just signals the display when the sensor senses engine/exhaust temperatures above the trigger level. Below the HOT warning temperature, the sensor does nothing, open circuit, no signal.

    It's only purpose is to warn of an unexpected and often sudden increase in engine temperature, typically caused by a sudden loss of water cooling. Disconnecting the temp sensor would have zero benefit or effect, until you have an actual engine overheat! That is the moment when having a working temp sensor might save your engine.

    The thermostat and pressure bypass valve, working together inside the thermostat housing, control engine water flow and engine operating temperature. If either of these is missing or not working then the engine temperature is not 'controlled' and is entirely subject to outside water temperature and jet pump water pressure through the cooling system.

    In normal operation, the thermostat limits water flow through the engine at idle and low RPM. This allows the engine to warm up properly, and prevents over cooling when the engine returns to idle after running at speed. The thermostat opens when the water leaving the engine reaches about 143F, and maintains the water flow at about that temperature.

    When the engine RPM gets nicely into the power band the jet pump delivers enough water pressure into the cooling system to push open the pressure bypass valve inside the thermostat housing. This allows increased water flow and increases engine cooling, more than enough to handle the heat from full engine power. Bryan reported that his engine temperature goes down when he is riding hard, then warms back up when he slows down.

    Some Polaris models actually have a flow restrictor inserted into the end of the water tube at the jet pump, to reduce the over cooling effect at higher RPM. Some models also have a spacer to increase spring tension under the pressure bypass valve and thereby raise the RPM level at which the bypass begins to open.

  9. #9
    Rasta Mon Condoms We Be Jammin!!!!! TxVirageTx's Avatar
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    the carbed 1200's don't have a t-stat or pop-off,maybe the x-45 does.the shim was to keep the pop-off closed all the time and make the t-stat do ALL the temp regulating.the fi stuff is suppose to be at a certain minimum temp or above.i have seen temp sensors that have hit the close circuit temp not reset afterwards.maybe thats why they cut it

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    I dont know of any Polaris motor that doesn't have the thermostat and popoff. My Pro 1200 for sure has it.

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