Coolant Alarm

Posted on Feb 7, 2014

My coolant level alarm has been working for the last 6 years, the alarm started to go off fairly regularly, although every time I checked the expansion tank, there was no problem with the level of coolant. Even with a cold engine, and using a screwdriver to push the float down, everything seemed okay. The problem

Coolant Alarm
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slowly became worse, until it was triggering virtually constant, and with the noise of the buzzer in the car driving me and my wife mad, there was no option but to disconnect the thing. Luckily, by having built a fuse into the 12v supply, it was simple enough to do. Stripping the circuit board out of the car, and bench testing it with an oscilloscope, I still couldn`t find a problem, so back in the car it went for further testing. I added an extra 12v light into the circuit, between the return wire from the hall-effect sensor and ground, so I would be able to see immediately the sensor tripped, rather than wait for the delay circuit to turn on the buzzer and the original led. However. while trying to static test it again, pushing the float down with a screwdriver, it failed to work at all. What did happen is when I pulled out the screwdriver, there was this small 19mm long magnet stuck to the end. ! What appears to have happened is that the magnet, fitted vertically into the float, has been slowly dropping out, triggering the alarm prematurely, but each time I tested the alarm, by manually pushing the float down to the bottom of the tank, the magnet has been pushed back in, only to slowly work it`s way out again. Since the float and magnet cannot be replaced, the only option was to purchase a new expansion tank. The float in the new tank appears to have been redesign, with the magnet or magnets being embedded in the float...

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