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300tdi coolant level sensor PRC7925 Wiring Help Please

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Ive got to the point where i desperately need to fit a coolant level sensor on my 300tdi as i dont want to spend another £2K on my engine

so i searched online and saw bits of info about using part no PRC7925 (Range rover 200tdi Header tank sensor/cap) and thought thats a brilliant idea so managed to find and order a brand new genuine one for £26

brill its arrived but how do i wire it up errrr confused tommy here :unsure:

so i searched online agaibn and can see bits of information all over the place but can seem to piece together a full solution so....

Can anybody Help Please?????

i believe ralph has done this mod in the past, can you remember how you did it????

thanks in advance


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Having overheated my engine and replaced it, I did exactly the same mod to prevent it happening again! The problem is that the Range Rover header tank sensor has a resistor in circuit, so it's not a simple case of wiring it up to a light.

I bought a purpose built unit (there is a thread on here somewhere!) in the Discovery area. A friend used the sensor to drive a transistor and then a lamp. His worked just as well. If I get a chance tonight I'll dig out the circuits.



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I have been looking at the very same thing and bought sensor PRC7925.

With the sensor in one hand and a multi meter in the other I'm finding that the sensor doesn't have any resistance when the level is high (i.e. switch closed) and is effectively open circuit when the level is low. The thing that seems to be in doubt is the current that the switch can cope with?

The basic circuit I'm looking at creating the attached circuit

Switch open (coolant low) light is on

Switch closed (coolant level fine): light off

S1 is the coolant switch.

R1 is 1k ohm.

I can't remember the transistor off the top of my head.

It would be easy to put a 'test' switch in series with the coolant sensor to make sure it works but I'm trying to come up with a circuit that has the warning light on for a few seconds when the ignition is turned on (there are a number of ways of dong it but come down to using a capacitor or the field terminal from the alternator).

Not sure how much this helps you but I'm happy to share the finished circuit.




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I just had a push button that bridged out the coolant sensor and triggered (in my case) the indicator and the alarm. That gave me confidence that it woudl work - granted it wasn't automatic but it was good enough for me.

The circuit shown earlier should be easy to knock up. I have some transistors and LEDs lying around if it helps.



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