Yanmar Engine Temp

[Papawads]

The Admiral has smelled a rat.... and is starting to get on my case about boat purchases "you don't even know what to do with", so help is required!!

Our Jeanneau model (SO 43 DS) has a coolant temp alarm but no gauge. Engine is 4JH3-TE.

I proudly installed a genuine Yanmar engine temp sender, into the coolant water pump housing. All good, much fanfare.

I have (in hand) a genuine Yanmar temp gauge.

Here's where I'm lost... the gauge has two terminal for wiring, and when tested with 12v goes over to total maximum/minium depending on polarity used.

The sender 'seems' to only have a single, screw down, terminal for single wire? So I think, it's a variable resistor, which is sensitive to temp. Indeed, I measure a positive resistance between terminal and thread (into coolant oump) when hot.

So to test, I send 12V +ve from source, through the gauge and out to sensor terminal and presumably to ground.

Whatever combination I try, on the gauge, it moves smartly to maximum or minimum stil, even on a fully warm engine.

What am I doing wrong???? We need a win.


Thanks :-)
Papawads

[Wotname]

Originally Posted by Papawads

.........

I have (in hand) a genuine Yanmar temp gauge.

Here's where I'm lost... the gauge has two terminal for wiring, and when tested with 12v goes over to total maximum/minium depending on polarity used.

The sender 'seems' to only have a single, screw down, terminal for single wire? So I think, it's a variable resistor, which is sensitive to temp. Indeed, I measure a positive resistance between terminal and thread (into coolant oump) when hot.

So to test, I send 12V +ve from source, through the gauge and out to sensor terminal and presumably to ground.

Whatever combination I try, on the gauge, it moves smartly to maximum or minimum stil, even on a fully warm engine.

What am I doing wrong???? We need a win.


Thanks :-)
Papawads

Something is incorrect here...
A 4JH3-TE genuine coolant temperature gauge has 4 connections (as do almost all temperature gauges).

+ve 12V (supply)
-ve 12V (return)
Instrument lamp
Sensor connection.

As you say, the sensor is just a simple resistance that varies with temperature. This is connected to the gauge. The gauge also has 12V +ve and -ve connection to provide power for the gauge plus a separate wire (+ve) for the internal lighting.

[knot smart]

my vote would be that youi have the wrong sending unit.. we have a ds43 with a 4JHG3-TE that i just rebuilt.. there are 2 different sending units.. one for an "idiot light" (thats the one we have) and one that controls a gauge..

i could be wrong but i think
144626-91570 SENDER UNIT is the one for the gauge

and

120130-91370 SWITCH, THERMO is the for the idiot light

contact these people to find out if im correct

https://shop.toadmarinesupply.com/ships_store/

i ordered all my parts from them..

[GordMay]

As Wotname indicated, there are usually 4 wires [12VDC Power “I”, Sender “S”, Light “Lt”, & Negative Ground “G”] to a typical temperature gauge, but the sender [to gauge] is often a single wire [‘S’], with an engine block negative [body grounded] return.
There are also [less common] 2-wire isolated systems, with a discrete negative wire.

See wiring diagram, below.

Temperature Senders are often Bi-Metalic Thermo-Couple, or Thermisters devices, whose resistance decreases, as Temperature rises [inverse relationship]; resulting in a higher reference voltage at the gauge.

Test Voltage between “I” Terminal (External Power Supply) and Ground Terminal “G”.
Tested voltage must match nominal voltage of the Gauge (ie: 12V Gauge must test between 10 - 16VDC), and the Battery Voltage.
If no voltage - check Ignition or Instrument Switch(s) and/or Fuses.
If tests less than battery voltage, repair or replace (Violet) wire from Ignition or Instrument Switch.

1. Disconnect Tan Sender Wire from Gauge (Terminal “S”) and turn Instrument Power ON.
The Temperature Gauge should indicate ZERO Scale (< Low Temperature).
2. Short the Gauge Sender Terminal “S” to Ground Terminal “G”.
The Gauge should deflect to FULL Scale (> High Temperature).
3. Measure Resistance from Tan Sender Wire (disconnected from Gauge) to Ground.
American Temp. Senders will read: 450 Ohms (Engine Cold @ 1000F)
or 29.6 Ohms (Engine Hot @ 2500F )
European Temp. Senders will read: 281 Ohms (Cold @ 400C) and 22 Ohms (Hot @ 1200C)
4. Disconnect Tan Wire from Sender on Engine Block.
5. Test continuity of Tan Wire.
Zero Ohms from Block End to Gauge End - If not, repair or replace Wire.
6. Measure Resistance from Sender Terminal (on Block) to Ground on Block.
Should read as per (3) above - If not, replace Sender.



Diagram https://www.cruisersforum.com/galler...=500&userid=79

See:
“Basic Engine Gauge Theory and Testing” ➥ https://www.cruisersforum.com/forums....html#post2597