Yanmar temperature switch 65°C for GM/HM – 128275-91340

Description

Yanmar temperature switch 65°C for GM and HM engines

The Yanmar temperature switch 128275-91340 is a temperature alarm switch for directly cooled Yanmar marine diesel engines from the GM and HM series. The switch is part of the temperature protection system and is designed to activate the temperature alarm when the cooling water temperature reaches the switching temperature of 65°C.

Reliable temperature protection is important for detecting engine overheating in time. When the cooling system is not functioning properly, the engine temperature can rise rapidly. The temperature switch helps the operator detect abnormal temperatures before serious engine damage occurs.

Technical specifications

Brand: Yanmar
Product type: Temperature switch
Function: Cooling water temperature alarm
Switching temperature: 65°C
Cooling system type: Directly cooled
Application: Temperature protection for marine diesel engines
Engine series: GM and HM series

Suitable for Yanmar marine engines

This temperature switch is used on directly cooled versions of the following Yanmar marine diesel engines:

Suitable for:
Yanmar 1GM
Yanmar 1GM10
Yanmar 2GM
Yanmar 2GM20
Yanmar 2GM20-YEU
Yanmar 3GM
Yanmar 3GM30
Yanmar 3GM30-YEU
Yanmar 3HM
Yanmar 3HM35

The correct temperature switch depends on the exact engine type and cooling system configuration. Before ordering, check whether the engine is directly or indirectly cooled and whether the specified switching temperature is 65°C.

How the temperature switch works

The temperature switch monitors the cooling water temperature in the engine. At normal operating temperatures, the switch remains in its normal switching position. When the temperature reaches the specified switching value, the electrical switch contact changes state.

This activates the connected temperature alarm. Depending on the engine installation, this may be a warning light or an audible alarm on the instrument panel.

The temperature switch is designed to activate an alarm. It is not a temperature sender for continuously displaying the cooling water temperature on an analogue temperature gauge.

Specifically for directly cooled engines

This version has a switching temperature of 65°C and is intended for Yanmar engines with direct seawater cooling. In this type of cooling system, seawater flows directly through the engine’s cooling passages to dissipate heat.

Indirectly cooled engines generally use a separate closed coolant circuit, where heat is dissipated through a heat exchanger. These installations may have a different normal operating temperature and require a different temperature switch.

When replacing the switch, it is therefore important to check not only the engine type but also the cooling system configuration and the specified switching temperature.

Why is a functioning temperature protection system important?

A marine diesel engine continuously generates heat during operation. The cooling system removes this heat to keep the engine temperature within the permitted limits.

When the cooling system is not functioning properly, the engine temperature may rise. Possible causes include:

Insufficient cooling water supply: A closed seacock or blocked water intake.
Clogged seawater strainer: Restricted seawater supply.
Damaged impeller: Insufficient cooling water circulation.
Blockage: Restricted flow in the cooling system.
Faulty thermostat: Incorrect regulation of cooling water flow.

The temperature switch helps detect excessive temperatures. The switch does not solve a cooling problem itself but provides important protection by warning the operator in time.

When should the temperature switch be replaced?

A faulty temperature switch may prevent the temperature alarm from activating when the engine overheats. A fault in the switch or wiring may also cause a false alarm.

If the alarm system is not operating reliably, the temperature switch, wiring, connections and instrument panel should be inspected.

Replace the temperature switch if testing shows that it no longer switches at the specified temperature or if the component is damaged.

Installation and replacement

Before replacement, check that the new temperature switch matches the specified version for the engine. Pay particular attention to the switching temperature, electrical connection and mechanical fit.

Only carry out work on the cooling system when the engine has cooled down sufficiently. Install the new temperature switch according to Yanmar’s instructions.

After installation, check that the connection is watertight and that the temperature alarm system functions correctly. Use the inspection procedure from the maintenance documentation of the relevant