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  #1  
Old 11-04-2008
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Thermo Switch?

I've got a plug on my Vetus motor on the Exhaust Injection pipe, just before it meets the heat exchanger. Vetus calls it a "Thermo Switch". This plug has a connection for a wire, but the is wire is missing, nor are there any gauges missing a wire.

Would this be a for a temperature alarm? I thought temp alarms were put somewhere in the system after the exhaust is mixed with the water, at least in a wet exhaust system...not that I can find that sending unit either, so I'm wondering if this is all I have for temp alarms.

Is there a way to test this? How does such a thing work? There's just one wire, so is the thinking done at the alarm the wire would run to?

Here's a scematic:


Thanks.
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Seagrass
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Old 11-04-2008
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PK,

I'm having a little trouble following your description. You say "on the Exhaust Injection pipe, just before it meets the heat exchanger". By "heat exchanger", do you mean "mixing elbow"?

Also, what is item #9 on the schematic? And what is #49 (including ##34&48)?

It sort of looks to me like the "thermo switch" is inserted into the exhaust opposite the point in the elbow where the raw water from the heat exchanger gets dumped in, in which case that might be a good spot to have the temp sensor. But usually when you have a heat exchanger, you're concerned about the internal coolant temp, not the raw water temp.
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Old 11-04-2008
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Thank John..see below

Quote:
Originally Posted by JohnRPollard View Post
PK,

I'm having a little trouble following your description. You say "on the Exhaust Injection pipe, just before it meets the heat exchanger". By "heat exchanger", do you mean "mixing elbow"?
Well, I may have my terminology incorrect. I'm calling the main thing in the center of the diagram, with "VETUS" on the side the Heat Exchanger, when specifically that would be part #36. Part #34 Vetus is calling a "Exhaust Injection Pipe". Truthfully I've not taken the time to trace it around to see if it's indeed straight exhaust (no water yet).

Quote:
Originally Posted by JohnRPollard View Post
Also, what is item #9 on the schematic? And what is #49 (including ##34&48)?
From the Scematic:
#9: Washer
#49: Injection Pipe + Plugs
#34: Exhaust Injection Pipe
#48: Plug G 3/8

Quote:
Originally Posted by JohnRPollard View Post
It sort of looks to me like the "thermo switch" is inserted into the exhaust opposite the point in the elbow where the raw water from the heat exchanger gets dumped in, in which case that might be a good spot to have the temp sensor. But usually when you have a heat exchanger, you're concerned about the internal coolant temp, not the raw water temp.
Good point about the internal coolant temp. I've got a single temperature idiot light on my engine guage panel. Don't know if it does anything though.

I think you are correct, now it makes more sense to me. The term "Exhaust Injection Pipe" threw me..Exhaust isn't being injected, it's getting injected with raw water.

I'm attracted to that sensor #8 below since I can easily get to it, and can easily rig some sort of temperature alarm, or even a temp guage if I was lucky. That is, if I can figure out what it does. "Thermo Switch" sounds like an all-or-nothing" sort of a thing.

Typically, how do these sensors work. If I remove the sensor, and heat it, what am I looking for (ie what does the wire transmit).
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Old 11-04-2008
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Generally

A thermo-switch is generally just that a switch. When it hits a certain temp it either makes or breaks. It was probably installed there to monitor raw water flow. If you lose raw water the exhaust temp rises, switch makes and sends signal to alarm buzzer. This is generally how a thermo-switch would function. That is not however where you would install a temperature sending unit. A sending unit and a switch are different.

If you want to install a sending unit look at your thermostat housing for any plugged tapings and this will likely be where the sending unit goes. On my engine I have both a thermo-switch and a sending unit. This motor is a Westerbeke but it's a Mitsubishi block. Many of the Vetus engines are also Mitsubishi's. This is a photo of my temp sending unit on the thermostat housing. The thermo-switch is opposite the sending unit and actuates the audible buzzer.

Look bellow the radiator hose and you'll see the sending unit. This sends the signal direct to my temp gauge.
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Thanks MainSail. It is a Mitsubishi block on this Vetus.

I'll take a look tomorrow for a sending unit too. I just want to be sure I've got something to give a warning.
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Old 11-04-2008
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If you find a

If you find a plugged tapping on the thermostat housing you can remove it and install a temp sender and gauge for about $60.00. The Teleflex temp gauges and sending units available from Hamilton, WM or any other chandlery will work just fine. All you need to know is the tappings thread dia and then buy teh coresponding sending unit to fit it..

I would personally never own a boat without a temp gauge. By the time a thermo-switch makes the damage may already be done in terms of a burned out impeller or over heated exhaust hose.

Follow this scenario. You suck in a jelly fish that blocks your raw water intake just as you leave the mooring. Becaue your water heater is still cold it sucks and transfers enough heat from the engines sealed system to prevent an over heat or alarm buzeer for another five to ten minutes, maybe more. Meanwhile your impeller is melting and your exhaust hose is being damaged beyond repair by a "dry" exhaust.

It's best to have both a gauge and an alarm in case one or the other fails. Most sailors would notice no water coming out of the exhaust but not all..

Temp Gauge $27.95 (LINK)

Sending Unit (LINK)
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Last edited by Maine Sail; 11-04-2008 at 11:01 PM.
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Excellent. I'll look tomorrow. Thanks for setting the scene there..I want a gauge.
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