Friday 31 August 2012

Yanmar 1 GM10c diesel, water temperature alarm fault

After a service and water soluable engine cleaning, I found that the audible alarm and red warning light was tending to go off, this was not all the time to start but soon became permanent.

I emailed our local Yanmar agents for methods to do a test on the sender unit.

The new sensor and its packing box.

Locally they are well priced and not a bad buy even as a spare? I found that local Yanmar support was good and the various workshop manual pages were scanned and then emailed to me.

Hi Roy,

Please view the attached - the unit can be tested by placing the water temp senders probe in boiling water.
Once the water reaches between 97 – 103 degrees.C for 60 seconds you should get a 12V / 1amp reading form your multi meter.

Kind regards,


I thought about this a bit and having already removed the unit to check that it was not just dirty, then finding it clean replaced it, I was prepared to just buy a new one and try it out.

The sensor will only work when its reached the above stated temperature, or if its got a closed and shorted circuit. With the sender unit wire off, the alarm did not go off, so in normal use the sender had to switch in to make the alarms work, that or when it developed a dead short as was the case on my engine.

The new sensor is now in place, I used PTFE thread tape to stop any leaks and the nice clean brass main body has been coated with Fluid Film to keep it looking that way.

A nice new Yanmar  1GM10 ready for shipping, its available right now at a discounted price. The sender unit to the raw water cooling can be found just below the injector and to the rear of the cylinder.

Note, this engine has since been sold.

This is Yanmars no frills basic panel (not the gauges) in normal use and when the key is turned, the alarm will sound and two lights will come on as seen. In my case the water sensor light was also working and when the engine was started it stayed on, while the oil and charger lights went out.

This was a simple fix for me, I hope it helps someone.


Note, as Yanmar agents we can supply parts to order and often ex stock, thats anything from gaskets,anodes, pistons,rings and bearings to sender units.