Yanmar 4JH5E issues

[Nz marine]

I have been contracted to do some work on a vessel with twin yanmars with 150 hours new.
The work has been to diagnose a temperature difference between the engines as port was believed to be running hot at 100C starboard engine running at 88C.
So far I have changed temp sender unit for new
Swapped thermostats between engines
Swapped engine caps between engines
Swapped engine gauges on fly bridge
Checked impellers and flow which is good
The problem persists...... high temp on port engine gauge.
A thermo gun on the port engine is showing 78C from thermostat to cooler with returning coolant from cooler at 58C, so I’m confident the engine is not running hot.
This has been an issue for them since they had the engines installed last year from day one upon turning on the key and has left me scratching my head which seems as though it is a sender unit issue but replacing has not solved the issue.
Does anyone have any ideas of where to look into next

[pcmm]

Have you swapped the temp sensors on the engines to see if the problem follows? If you swap them and the problem persists, there is some sort of wiring issue

[Nz marine]

Hi there
Have not tried swapping the sensors but I have replaced the sensor with a new one on the port engine with the problem persisting and giving the same reading.
I believe it could be a wire issue as the sensor relies on internal resistance using the engine as its neutral so any sort of resistance in the cable is going to give a faulty reading I believe
Electrickery........

[pcmm]

Originally Posted by Nz marine

Hi there
Have not tried swapping the sensors but I have replaced the sensor with a new one on the port engine with the problem persisting and giving the same reading.
I believe it could be a wire issue as the sensor relies on internal resistance using the engine as its neutral so any sort of resistance in the cable is going to give a faulty reading I believe
Electrickery........

Moving or swapping the sensors between engines will also confirm that the new sensor is behaving as expected. Its not unheard of for a brand new sensor to be bad.

[donradcliffe]

The sensors are variable resistance device, and any bad connection between the sensor and the gauge can cause your problem.

Here are some troubleshooting clues.

https://www.samarins.com/glossary/co...re-sensor.html

[jamhass]

Have you tried swapping gauges?

[Rapanui]

It does sound like a wiring issue. You could use a multimeter to measure the resistance of the wiring. Short out the temperature sensor and measure the loop resistance at the gauge. Yanmar engine looms have been known to go high resistance at the multiway connectors and cause failure to start. I would break each connector, treat with electrical grease and re- connect.
Another option would be the voltage energising the gauge may be different between engines. I would expect some sort of stabilised power supply so that gauge readings do not fluctuate with battery volts so worth checking

[GordMay]

Greetings and welcome aboard the CF, Nz marine.

See also:

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

Testing Engine Gauges
1. ➥ https://www.cruisersforum.com/galler...r&imageuser=79

2. ➥ https://www.cruisersforum.com/galler...r&imageuser=79

Engine Gauge Wiring Diagram
➥ https://www.cruisersforum.com/galler...r&imageuser=79