Overheating is the No.1 biggest killer of Tdi engines. If there is a leak a loss of coolant can go unnoticed until its too late. My misses recently killed my 300tdi in such a scenario and I have been paranoid ever since fitting a new lump. Landrover defender are not fitted with coolant level warning where as RangeRover tdi's are. Lucky enough the Rangie's coolant expansion tank cap with level sensor fits the defenders bottle.
Wiring up the sensor is not so straight forward as the range rover feds through a 'module'. The sensor float is resistive rather than simple on/off. Without the module you can not wire a up a normal automotive relay to the circuit, it simple will not switch. Google turns up other peoples methods of installing one of these caps, this is mine and uses stuff I already had so didn't cost me anything.
In my electronic junk boxes I found a suitable 'no-volt' relay which will trigger by the sensor (I used to be a mechatronic tech so have some nice junk). For added bonus feature, this was a multi function timer relay which allowed me to wire it up so that only after 6 seconds of the sensor detecting a low level situation it will then trigger the alarm. This delay should prevent false alarms in extreme offroad situations where the coolant level will bounce the sensor around.
The alarm is an electronic audio alarm.
The relay and alarm are installed behind the instrument pod. A visual alarm can by also be wired to one of the unused dash warning lamps.
Main Components:
EXPANSION TANK SENSOR LATE RR PART No: PRC7925
RELAY - Multi Function Timer, RADIO SPARES STOCK No. 341-389
ALARM - Pulse tone Klaxon RADIO SPARES STOCK No. 249-788
Relay timer Wiring:
B1: WIRED to one spade terminal on LEVEL SENSOR CAP.
B2: Wired to the other spade terminal on LEVEL SENSOR CAP.
A1: +12 volt live with ignition on. Also link wired to 15.
A2: -12v Earth. Also wire to negative side of alarm.
15: Link wire routed to A1.
16: Wired to positive side of alarm.
A 12volt warning lamp can also be wired in parallel between 16 & A2.
The timer relay function dials are set to "RELEASE DELAY", "0.6-6 SEC" and the red multiplier dial set to "6", maybe a blob of semi setting glue to fix it in position.
That's all there is too it :D, works well. The alarm might give out a little chirp as ignition is turned on by the key. The system is partially fail safe as in if the relay fails internally the alarm will sound, if a wire to the sensor cap breaks the alarm will sound.
EDIT: As an alternative to the circuit. The alarm stays wired as stated but the warning lamp can be wired between 18 & A2. The logic to this is that the warning light will stay illuminated showing the circuit working, if there is low coolant, the lamp will go out and alarm will sound, if there is no lamp and no alarm then circuit is at fault. A fuse can be placed on the positive feed in this arrangement too, non lamp illumination would show a blown fuse.
Question: Does the range rover module have built in timer, if not then is this the reason why it not fitted to defenders which naturally see more extreme offroad conditions and possible false alarms without a timer?
