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318 over heating water and shutting down

Heuzy

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Oct 23, 2013
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Hi guys. My engine is over heating and cutting out with what seems to be a dema valve issue. There is some hot water dumping into the tank but that only seems to be coming from the thermal valve on the waterbox. The dema valve doesn't seem to be getting any power to it, to open and dump the extremely hot water. The engine was removed recently to replace a crankcase gasket and i wonder if it hasn't been wired up properly. There is also a red wire that my small engine mechanic can't find a connection for (photo attached)]. I have also descaled to try and eliminate that. Any ideas or photos would be appreciated. 2009 model.
 

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brian3180

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You should be able to hear the dema valve engage if you turn the key to the "ON" position.
 

wandwizard

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Every dema solenoid that I've seen go out always stayed open and dumped water. I've never personally seen one do otherwise and stay in the closed position. If you haven't already done so make certain your orifices are clear. Even descaling won't clear them. I always make sure mine are clear after every descaling. Just a small spec of scale can clog it and your machine will overheat rapidly and shut down.

A simple way to see if your Dema is opening and closing is to let the machine heat up a few minutes with your temp knob turned all the way up. When your machine reaches about 180 or so simply turn the temp control knob down below 180 and watch your psi guage. If the Dema is operating you will see it drop maybe 100 psi or so. Then turn the temp dial back up and you should see the psi go back up. That is your solenoid working when that happens. That extra wire could be for an accessory that you are not using, for example, an APO or a freshwater pump in. You can also take the waste tank off and after your machine is hot use the temp dial and see if the water is dumping. The 12 volt coil is what usually goes out on those or perhaps some scale has gotten in there and clogged it up. You may have to take it apart and make sure it's clean if you find it's not dumping. Just make sure you put it back together in the correct order.

If the water in your water box is getting way too hot I would first suspect a bad thermal relief valve. That will cause that water to reach boiling hot temperature in the water box very fast and your machine will shut down.

Right now, I'd plan on going ahead and buying a new Dema solenoid. It should be a 453P, but you better confirm that before you order. It is available at a number of places online for probably 50 to 80 dollars. This should be your solenoid, but Jondon is 2 or 3 times what the price should be for this. https://www.jondon.com/solenoid-high-temp.html
 
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wandwizard

Randy Dockins
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Hi guys. Turns out i do have electrical current going to the dema with the machine running. Have just ordered a new dema so hopefully that will solve my problem. Thanks for your help.
Occasionally some crud can get into your Dema and prevent it from letting the water through so the machine can't cool itself down. It is fairly easy to take it apart and make sure. If you're sure it's getting power and not working chances are your 12 volt coil is out. Those are replaceable btw, but I always suggest keeping a spare working solenoid as well as a spare thermal valve on hand all the time. Either one can mess your day up if they go bad.