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Thermostat circuit diagram

Toonl

Regular Contributor
I have an upper and lower helm station so I have two temperature gages. Yesterday I noticed that I have a temperature sending unit at the thermostat housing, and also one in the water jacket of the exhaust manifold, per engine. The electrician in me is wondering how two sending units could be connected in series and still work properly, or is there some magic at work here? Does anyone have a circuit diagram that show how these should be connected?
 
temp switch will most typically have two leads coming from it, while senders have a sing lead and use engine ground as the other.

possible if they are both senders that one is used for each station. disconnect one and see if one gauge goes dead.
 
Dual station boats are typically set up with the helm harnesses being parallel with one another.
There is a different temp gauge sending unit for either single or dual stations.
A dual station sender operates both helm temp instruments.


.
 
They are both sending units I'm thinking, because they only have a single lead coming from each one. Does anyone have a wiring diagram of a dual station, dual engine system? I'm gong to disconnect the exhaust manifold sender and see what effect that has.
 
Original situation
The port engine sat at 160 degrees and would climb to 200 when the RPMs increased to 3000 RPMs.
Once I removed the exhaust manifold sending unit wire I could see the thermostat cycling between 160 and 180.
I will know better on the next run.
Starboard engine
Originally indicated at or around 140 degrees when warm.
After removing the exhaust sending unit wire the engine indicated 120 degrees.
I suspect I am going to have to replace this sending unit.
Does any one have the correct part number for a dual gage single sender?
I suspect the exhaust manifold senders were interfering with the engine senders.
 
There are single and dual helm sender units. Most are generic and fit many temp gage systems. I got mine from the Blue Box store (initials W M)

Jeff
 
As far as the gauge (pressure or temp) wiring goes, there should be ONE sender on an engine. The lead from the sender should go to the S input on each gauge (single or dual station setup). The sender changes when you have dual stations. Volt meters and tachs are wired similarly (but no 'sender units' for them on a gas engine).

disconnecting one of the 'sender units' and having the gauge change infers something wasn't wired correctly.

Finally, be aware that some gauges require unique sender units....this is more of a concern with older installations.
 
So this is what I have managed to find out. The sending unit at the thermostat is a thermistor which passes current, affected by temperature. The higher the temperature the higher the mount of current it passes. The temperature gage follows that current swing and changes the gage display, the higher the current the higher the temperature reading. The second sender in the exhaust manifold is actually a thermal switch with a single lead. This switch shorts the sender lead to ground and therefore swings the temperature gage to the full hot position if it trips.
 
that's one way of describing it.....the switch would be better hooked up to an alarm (buzzer) so it will get your immediate attention..
 
This is true but the current wiring configuration is what I was describing. I would have to rewire the overtemp switches to both helm stations to accomplish what you describe but it would be a better way to go.
 
This is what I appear to have on our boat. The previous owner added a secondary heat exchanger to the cooling circuit but I wonder if it was placed in the correct location. Your thoughts?
 

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This is what I appear to have on our boat. The previous owner added a secondary heat exchanger to the cooling circuit but I wonder if it was placed in the correct location. Your thoughts?

From your diagram, I would guess that you have 2 oil coolers. One on the transmission and one for the engine oil. I think what you refer to as a secondary heat exchanger is your engine oil cooler.
 
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