Yanmar Temperature Sensor 128275-91340

Function and technical context

This temperature sensor is part of the marine diesel engine cooling system, being responsible for continuously monitoring the temperature of the liquid or block and transmitting that signal to the instrument panel or the boat's alarm system. Its correct operation allows overheating situations to be detected before they cause serious damage to the cylinder head, gaskets or pistons. Located in the thermostat section of the parts (section 39, callout 8), it works closely with the thermostat and the seawater pump, being a key element for monitoring the thermal state of the propellant. If the sensor fails or drifts in its reading, the engine can overheat without activating the corresponding alarm, putting both the propeller and the safety of the boat at risk.

When to replace this part?

The most common symptoms of a faulty temperature sensor are erroneous or unstable readings on the panel temperature gauge, intermittent activation or complete absence of the overtemperature alarm, and in some cases the alarm light that remains on without actual overheating. It is recommended to check the sensor during each seasonal maintenance, especially if corrosion deposits are seen on the connector or housing thread, since marine humidity accelerates its degradation. Replacing it preventively if there is any doubt guarantees that the engine thermal protection system works reliably at all times, avoiding costly repairs due to seizure or damage to the cylinder head.