Playtime
Well-Known Member
I am getting what I think is a false overheat alarm on my D2-40. Using an IR thermometer the hottest temperature I can find is around 85C when the alarm triggers and this ties in with the sensor (thermistor) resistance (disconnected) I measured of 65 ohms according to the spec in the Volvo MDI manual. Water flow (raw and coolant) is as it should be and the engine does not feel/smell hot.
My understanding of the EVC/MDI Control Box (bolted to the port (alternator) side of the engine) is that it puts out a reference voltage of around 5V (I measured 5.3V open circuit) to the sensor. As the engine warms up, the resistance of the thermistor drops and hence the voltage drops too. The alarm should trigger when the temperature reaches 110C which equates to a thermistor resistance of around 29 ohms according to the Volvo manual. Mine is triggering at a much lower temperature/higher voltage.
Everything else on the EVC works as expected (oil pressure warning, alternator alarm, tacho).
My questions (at last) - has anyone had a similar problem and/or attempted to repair the MDI box?
Since a new box is upwards of £450 I am not keen to replace it on the off-chance it might fix the fault or to tinker with it unless I know its fixable. I also don't want to permanently disable the overheat alarm.
All (constructive) suggestions gratefully received.
My understanding of the EVC/MDI Control Box (bolted to the port (alternator) side of the engine) is that it puts out a reference voltage of around 5V (I measured 5.3V open circuit) to the sensor. As the engine warms up, the resistance of the thermistor drops and hence the voltage drops too. The alarm should trigger when the temperature reaches 110C which equates to a thermistor resistance of around 29 ohms according to the Volvo manual. Mine is triggering at a much lower temperature/higher voltage.
Everything else on the EVC works as expected (oil pressure warning, alternator alarm, tacho).
My questions (at last) - has anyone had a similar problem and/or attempted to repair the MDI box?
Since a new box is upwards of £450 I am not keen to replace it on the off-chance it might fix the fault or to tinker with it unless I know its fixable. I also don't want to permanently disable the overheat alarm.
All (constructive) suggestions gratefully received.