Yanmar overheat alarm

[LEC]

My 42 year old Yanmar alarm has started going off after the engine has been running for about two hours. Water still is pumping out and temp measures are 130-140 with infrared thermometer. Mechanic has checked all components of exhaust system and replaced thermostat. Within 15 minutes of shutting down the diesel, restarts without alarm sounding.

Any ideas?

Annoyed in the PNW

[Bycrick]

The fairly obvious answer is that the 40-year-old switch has gotten "old" and no longer closes at the originally specified temperature. Some options are:
1. Remove the switch from the engine. Get a verified thermometer. Attach an ohmmeter or other indicator across the switch. Put the switch in water on the stove and see when it closes. This is probably the least costly way.
2. Replace the switch first. This saves you work messing around with the old switch.

Neither one is a sure-fire optimum solution. In case 1, you’ve spent time diagnosing the problem. If it’s not the switch, you still need to find the problem, and you’ve wasted the diagnostic time/effort.

In case 2, you’ve bought a currently unneeded spare and still have to find the problem.

It depends on whether you have more time/curiosity than money, or Vice versa.

[skipperpete]

Originally Posted by LEC

My 42 year old Yanmar alarm has started going off after the engine has been running for about two hours. Water still is pumping out and temp measures are 130-140 with infrared thermometer. Mechanic has checked all components of exhaust system and replaced thermostat. Within 15 minutes of shutting down the diesel, restarts without alarm sounding.



Any ideas?



Annoyed in the PNW

Do the overheat alarm and the low oil pressure alarm have individual warning lights? Is it possible that what you’re hearing is a low oil alarm, not an overheat.