P38 Range Rover Low Coolant Alarm

One thing missing from the P38 is a low coolant alarm, this is a much needed addition in my opinion. There are basically three parts to a low coolant alarm, the sensor, the wiring and the alarm circuit, I will deal with each separately.

Sensors There are a couple of options for sensors, I believe you can use A BMW E10 expansion tank A sensor built into the cap of a late model classic A DIY option using stainless steel screws A DIY option using a float I chose the DIY option and used two 80mm 316 grade stainless steel screws, these are deep enough (I hope) to stop false alarms. Click on the image for a larger version

Wiring While you have the tank out, you can run the wiring for the alarm. I ran a length of five core cable since I want to add Lights and an Oil Pressure Gauge in the future Remove the kick panel and footwell cover from the drivers side under the steering column. If you feel up under the dash area at the bottom, you can feel where the wiring loom comes through. Two of photos below show the wiring exiting from under the bonnet and the third shows how I soldered a piece of wire coat hanger to the five core cable. The stiff coat hanger wire makes it pretty easy to feed through by feel from the inside under the dash, an assistant is handy for this job. Behind the coolant expansion tank where the loom comes through the firewall. With the extra 5 core cable fed through. Length of stiff wire soldered to the end of the cable.

Alarm There are a number of alarms on the market, I chose to use a more DIY approach. I bought a simple, now the older version, of an alarm from UK eBay seller pw928gts. The version I got did not have a test switch or an LED. I bought a flashing 12V LED from Jaycar electronics, it came in suitable mount. I thought about a test switch but decided that was a bit too manual for a Range Rover ;-) so I bought a 12V delay on board, the kind of thing used for speaker turn on delay in hi-fi systems. This means the circuit is held open for a few seconds, adjustable, after the ignition is switched on, triggering the alarm. I attached the electronics to the underside of the kick panel and fitted the LED next to my LPG switch and hooked it all up. While it may look a bit complicated, the timer simply goes in line with one of the sensor wires, it can be left out for a more simple installation Electronics attached under the kick panel. Drilled and paint removed to attach earth point connector. Earth point in place.

It works! I now have a 3 second racket and flashing LED each time I start the Rangie. As at Oct 2013 I have yet to test it out offroad to find out whether false alarms are triggered. I hope this information is helpful to some, it is not a complete round up of solutions, some owners prefer to fit an engine temperature alarm. More pics will be added soon All feedback, comments and corrections are very welcome, send to the email address in the home page.