Yanmar 4Jh5E overheating

[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
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 the had the engines installed last year from day one 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

[tkeithlu]

Hmmmmm.

Consider: Use the heat gun as an independent source, determining the steady state (warmed up, fixed RPM) temperature before and after the heat exchangers of both engines. If for any number of reasons one heat exchanger is not removing as much heat from the coolant as the other, it is sending hotter coolant back to the engine, which will very soon indicate that it is running hot. It isn't; it's just adding its heat to hotter coolant.

Second. Consider fuel flow to each engine. If one is running a bit rich, its exhaust temperature will be lower and it will send less heat to the coolant.

[pcmm]

Isn't this a duplicate of your other post, "Yanmar 4Jh5E issues"?

[flightlead404]

Originally Posted by 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
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 the had the engines installed last year from day one 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

If the engine is not running at the indicated temp, and you've replaced the sender and the gauge, then there's only one thing left. Check the harness for high resistance including the connectors. Are they N or K type thermocouples? Using the correct wire? Is the thermocouple wire significantly longer on one side compared to the other?