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300Tdi low coolant level warning - mystery component


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At last, I am attempting to install a low coolant level warning device on my 300Tdi. Some time ago I acquired, and I can’t remember where from, a Water Level Monitor, model Aqua 20 A8-IS117, according to the label on it. At one time it used to be supplied by Partline Ltd., but they have not handled these since the mid-nineties. There are no instructions with it. There are 6 electrical connections on one end, but no indication what they are for. I seem to remember that it can be connected to the RR coolant level probe PRC7925. Yes, to my shame, it’s a “blue box” jobbie!

Please can anybody advise me the duty of each connection, and if it can be used with PRC7925?

Many thanks, in advance, for any information members can supply.

Mike

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Just working on the logic of it...

1 power

1 ground

1 to sensor

1 back from sensor (maybe)

Then it depends on how self contained it is

1 to warning

1 back from warning

That's the six connections.., good luck figuring out which ones are which, you probably need to open it and put some pictures up :)

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Is that sensor just a switch or something analog? If a switch you dont need the box.

As steve says, take the top off and trace what you can, unless its potted. Even if it is some deduction with a DVM will get you the pinout

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Many thanks, all, for your replies and the info. Yes, Pete3000, you do get a prize - my unending gratitude :i-m_so_happy:, which will be renewed and reinforced if this mod saves me from a costly rebuild. And thank you, Maverick, for finding your 2013 thread. To my embarrassment I found that I had actually contributed to that thread, though I have no recollection of having done so. :blush: Old age strikes again!

Regarding your question, HoSS, as far as I know, it's a standard RR low level detector. I don't know what technology it uses, but the float only travels 10mm. between its upper and lower stops. Even using a stethoscope I can't hear any reed switch in the probe shaft operating. The float appears to be of hard plastic, and I can't detect any magnetic sensitivity in it, so I doubt if it activates a reed switch. In one of the many threads I read before posting there was a mention that it could rely upon conductance/conductivity/electrical properties(?) of the water, technology that is beyond me. :unsure:

Now to install the bits and see if they work. I have an LED I can use, but will have to buy a buzzer. This warning system is so critical that reliance on only an LED is overly optimistic. If I find anything that contradicts the info in the replies I’ll update this thread.

Many thanks again.

Mike

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A reed switch probably wont pass enough current for a relay, so the box has a transistor to switch further circuits. The box does give you flashy & delay functions. One could do it without the box, but since you have it.

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I believe the Range Rover sensor goes between about 680 ohms and several meg ohns, and does not go open circuit, which can mean difficulies in driving a relay directly. Also I have found even a very small low current relay draws more current than the RR sensor can live with for long. Some sort of device that can measure the change in resistance over that range without putting any load on the sensor is required.

I have also found that with the RR sensor in a 300TDI tank the fluid level drops quite a lot before the alarm is triggered. If the alarm goes off water is already very low, and it is necessary to stop and investigate quickly, given the low tolerance of the 300TDI to low water level..

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I believe the Range Rover sensor goes between about 680 ohms and several meg ohns, and does not go open circuit, which can mean difficulies in driving a relay directly. Also I have found even a very small low current relay draws more current than the RR sensor can live with for long. Some sort of device that can measure the change in resistance over that range without putting any load on the sensor is required.

I have also found that with the RR sensor in a 300TDI tank the fluid level drops quite a lot before the alarm is triggered. If the alarm goes off water is already very low, and it is necessary to stop and investigate quickly, given the low tolerance of the 300TDI to low water level..

Has anyone autopsied one of these sensors? It would be nice to know how they were made.

What I know for sure is if you purchase at least one make of sensor today it's a reed switch.

There isn't a published specification for the current rating of the reed switch but there are plenty relays out there that only need a very small current to operate, the one I used only needs 25mA for the coil and the contacts are plenty big enough for a flashing LED and buzzer ( 3 quid from China )

The only downside to this simple setup is no damping, mine will alert if I stand on the brakes hard as the water moves in the reservoir

At first I thought I would add damping but it's not annoying and I suppose it reminds me it's still working.

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Has anyone autopsied one of these sensors? It would be nice to know how they were made.

What I know for sure is if you purchase at least one make of sensor today it's a reed switch.

There isn't a published specification for the current rating of the reed switch but there are plenty relays out there that only need a very small current to operate, the one I used only needs 25mA for the coil and the contacts are plenty big enough for a flashing LED and buzzer ( 3 quid from China )

The only downside to this simple setup is no damping, mine will alert if I stand on the brakes hard as the water moves in the reservoir

At first I thought I would add damping but it's not annoying and I suppose it reminds me it's still working.

Yes Tim did when he made the modules for Difflock here http://forum.difflock.com/viewtopic.php?t=10972&highlite=300tdi+coolant=level+switch

I had a small buzzer in the dash panel, Being deaf I could hear it quite well, I eventually removed it and now rely on the warning light

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Yes Tim did when he made the modules for Difflock here http://forum.difflock.com/viewtopic.php?t=10972&highlite=300tdi+coolant=level+switch

I had a small buzzer in the dash panel, Being deaf I could hear it quite well, I eventually removed it and now rely on the warning light

I've read a lot of the threads and just re read the one quoted above , I can see reference to the resistance change but no actual , I cut it up and this is what's inside , just very curious to see what it was.

There are advantages to a switched resistance change if you need to automatically prove the switch.

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Yes Tim did when he made the modules for Difflock here http://forum.difflock.com/viewtopic.php?t=10972&highlite=300tdi+coolant=level+switch

I had a small buzzer in the dash panel, Being deaf I could hear it quite well, I eventually removed it and now rely on the warning light

I've got one of Tim's modules, works very well with my RR low coolant cap/switch. you'll notice some of the replies in the link are mine :i-m_so_happy:

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  • 4 years later...

Sorry to dig up an old thread, but would that cap be able to run a simple dash warning light fed directly from the fuse box and using nothing more than the two terminals in the cap, the feed and an earth through the light?

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13 minutes ago, elbekko said:

No, as it's the wrong way around. You need some way to invert the signal.

Ah, so rigging one of those inverting relays would sort it (pin 56A or 57A - I can never remember the numbers)?

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