Water Temprature Switch

[Charlie]

Just finished rebuilding engine on my generator. Running through some tests on a simple electrical system. I have a water temp switch that is supposed to cut the power to the run solenoid when the temp is too hot. If that is the case there should be continuity through the switch until it gets too hot. The oil switch on the other hand should have no continuity if there is no oil in the engine. I'm pretty sure I am right but thought I would check with the general knowledge here before getting ahead of myself.

[Wotname]

In principle, that is correct.

Re the oil switch, this is usually an oil pressure switch so it requires oil pressure rather than oil quantity.

The temp switch will be either a normally open or a normally closed switch. You have described a normally closed switch which would work in the circumstances you have described.

[DougR]

In addition to what has been said by Wotname, some generators also have a switch in the exhaust mixing elbow that is normally closed, but opens if the elbow temperature gets too high. This provides protection against impellor failure. All three of these switches ( water temp, oil pressure and exhaust temp.) are connected in series in the run solenoid circuit and provide the engine protection circuit. If any one of them opens the engine automatically shuts down.

DougR

[transmitterdan]

Most temp switches are normally open. Most oil switches are normally closed. That means the oil switch will have continuity when the engine is off. The temperature switch will have continuity only when the engine overheats. They are usually wired in parallel to the stop circuit. If either switch turns on it will ground the stop circuit which kills the fuel pump thus the engine stops. This means only one wire is required per switch. So if your switches are wired with only one wire each then it probably works as I described above. The wiring diagram of your generator should show all of this.

[a64pilot]

Water temp switch can sometimes be tested like a thermostat, connect a multimeter and put it in boiling water.
Be sure of course that it's set point is below 212F, if it's a little higher, boiling water of course maxes out at 212F

Of course an oil pressure switch is easy to test by connecting the multimeter and starting the gen, you should get an open with it running and closed with it off, I've tested the circuit by shorting to ground the oil pressure switch, the gen should die.

[Moody46CC]

Charlie,

You have some conflicting advice--Wotname says generally closed switches; transmitterdan says the opposite. Not much help.

I have a Mastervolt Genset with a Mitsubishi. It has three safety shut off switches: oil temp, oil pressure, and water exhaust temp. The operator manual says, "All alarm switches are closed when no malfunction occur[sic]. A contact is cut in the event of an alarm. This means that the generating set will not work when the alarm switches are broken or there is a loose wire. The system therefore is intrinsically safe." I think this id Dutch-English for a closed system. The sensor has two leads.

I had a bad hose that collapsed and destroyed an impeller. The water exhaust temp switch was, according to the mechanic, not working as well. Got a replacement switch, and when I pulled out the malfunctioning switch it was charred on the senor end! But I guess that would happen w/o any cooling water since the impeller was a vaneless nub.

So this weekend I'll install the new switch. The old one had some sort of a gasket around it. Did not look to be a paper one; more of a silicon one. The parts manual does not show a gasket in the blow-up or list one. The sensor is brass as is the fitting on the exhaust elbow where it goes. I plan to just use some Teflon tape on the threads instead of a gasket. Have you encountered this problem?

[Charlie]

Originally Posted by Moody46CC

Charlie,

You have some conflicting advice--Wotname says generally closed switches; transmitterdan says the opposite. Not much help.

I have a Mastervolt Genset with a Mitsubishi. It has three safety shut off switches: oil temp, oil pressure, and water exhaust temp. The operator manual says, "All alarm switches are closed when no malfunction occur[sic]. A contact is cut in the event of an alarm. This means that the generating set will not work when the alarm switches are broken or there is a loose wire. The system therefore is intrinsically safe." I think this id Dutch-English for a closed system. The sensor has two leads.

I had a bad hose that collapsed and destroyed an impeller. The water exhaust temp switch was, according to the mechanic, not working as well. Got a replacement switch, and when I pulled out the malfunctioning switch it was charred on the senor end! But I guess that would happen w/o any cooling water since the impeller was a vaneless nub.

So this weekend I'll install the new switch. The old one had some sort of a gasket around it. Did not look to be a paper one; more of a silicon one. The parts manual does not show a gasket in the blow-up or list one. The sensor is brass as is the fitting on the exhaust elbow where it goes. I plan to just use some Teflon tape on the threads instead of a gasket. Have you encountered this problem?

Yes there is conflicting info. I guess it can be designed either way. I think that mine is designed the way I described. I think this because of the continuity tests I ran on the switches. I guess I could go to the designers info on the switches and try to figure it out.

The sensor on my engine has a brass theaded insert that screws into the engine and a plastic and epoxy sensor with electrical leads that screws into the brass insert. the joint between the two has silicone around it. I like to use permatex #2 or hi temp thread sealer instead of teflon tape.

[Charlie]

@ Wotname. Thanks for the info. pressure switch makes more sense especially given where it it.

@DougR My genset does not have an exhaust sensor. but the temp and oil are wired series and if either one sees a problem will stop the engine.

@ trans mine must be the oppisite of what you suggest. they are wired in series.

@a64 thanks for the idea on how to test the sensor. I should have thought of that myself.

[transmitterdan]

Some generators are wired with a single parallel circuit where grounding cuts the engine. Some are the opposite with series loop where opening cuts the engine. I recommend checking the wiring diagram to be sure.

[Charlie]

Thanks for all the help. I looked up the manufactures spec on this switch and it is a normally closed switch. I tried testing it in boiling water but wasn't able to get it to open. The water temp was only 203*F according to my cooking thermoneter. Accourding to an online calculator I should be at 207*F. I don't think there is anything wrong with it so I will put things back together and run the generator for an hour before reinstalling it on my boat.

[Cheechako]

From your post... it sounds like your solenoid is normally activated when the engine is running.... correct? For the water side, you could just use a "snap disc" thermostat from Grainger etc to control that. You want a "normally closed" one.

[Wotname]

Originally Posted by Moody46CC

Charlie,

You have some conflicting advice--Wotname says generally closed switches; transmitterdan says the opposite. Not much help.

......

Err... no.

I said water temp. switch can be either NO or NC and that in the circuit as described by the OP, a NC switch could be used.

However depending on the circuit design, either can be made to work.

I would suggest the majority of water temp. switchs when used to light an warning light or sound an alarm are NO.

Oil pressure switches are NC.

In the situation of engine switches, the "normal" condition is when the engine turned off, i.e. not running!