Temperature alarm

[PhilB]

Just came back from gentle cruise and temp alarm sounded. Plenty of water flow. I presume the sender is on the right of the engine looking into compartment MD2030 Bav 36? With oil pressure on left (screw connection).  I let engine cool and alarm still sounds,  stops if i pull off the wire to the sensor on the right. Sensor has some resistance to earth if I measure,  I assume it should be open circuit when engine cold. Anyone had any experience?

[Yngmar]

Let's have a look at the service manual: http://www.baadteknik.dk/Manualer/Motor/Volvo-Penta-MD2010/Volvo-Penta-MD2010-20-30-40.pdf

It seems that engine has both a refrigerant temperature relay (closed circuit above 95/100°C) and a refrigerant temperature sensor (a NTC, meaning resistance goes down as temperature goes up). Which one is used depends on which engine instrument panel you have.

I'm assuming you have the standard panel (RPM gauge and alarm lights only, no temperature gauge). In this case the temperature sensor doesn't seem to be wired to anything, only the relay is used, which goes straight to the warning lamp on the panel and should go off (relay closes circuit) if the temperature is over the above limit.

The refrigerant temperature relay is no. 11 on the attached picture (12 being the unused sensor).

[PhilB]

Many thanks for this and the link to the excellent manual. I  have the standard panel so I think the sender should be open circuit until the temp is exceeded. Think Ill try a new one,  despite the ridiculous cost