Just done an engine swap in the Fury and been updating a few other bits that I've been wanting to sort for ages.

I have a VW "globe" type coolant bottle with levelsensor. As I understand it, the level sensor on the VW coolant bottles uses the coolant to complete the circuit when the level is correct (rather than a float that switches when the levelis low). Mine was wired (mistakenly) to come on when switched and as a result was constantly on (luckily only a dim LED) since I built it. So I took the opportunity to re-wire it through a (normally closed) relay while the engine was out of the way so the light would be off when the level was OK and... it's still on!

I suspect the sensor isn't able to carry enough current to switch the relay; Shorting the sensor wires together (and so earthing the relay) puts the light out, so looks that way... or do I have a dodgy sensor/bottle?

Has anybody managed to use the VW sensor for a dash warning light? Could it be done with some sort of electronic circuit?

The other alternatives are either disconnect and forget, or replace the VW bottle with one using a float type sensor.

[Edited on 13/3/13 by adithorp]

Unfortunately I don't think it's quite so simple.

You want to avoid having current ever flow constantly through a coolant sensor like that because it'll cause electrolysis which will corrode the terminal, and potentially put nasties in your coolant (less of an issue).

I'm pretty sure the VW's use a control box to interpret the resistance from the sensor and then drive the LED from there.


This may or may not shed any light on your problem, but seems to confirm the above:

http://archive.club8090.co.uk/viewtopic.php?p=7327754&sid=41e5ecc1ed04633c198c695ba13bdbd4


Please don't take this as gospel, it's just my understanding of the system.

Thanks for the link. Just had an e-mail from an Audi tech I know and he says coolant density (mines OK) and oil contamination (possible from the old engine) are known issues and sensor failure isn't unknown. He's getting back to me with a sensor resistance reading. That link indicates a sensor resistance of 60k ohms and I've just tested mine at 500k ohms so I suspect my sensor.

Yes, I'm aware of the electrosis issue.

It needs a custom electronic circuit to work, the same sort that is used in aquairiums a search on ebay should trawl up a few (no pun intended).

I would only wire to check the level on start up because the coolant splashing around when cornering will cause false alarms.

Low Water Level Alarm 12V Built And Tested | eBay


WATER LEAK DETECTOR MODULE - WATER TANK LEVEL SENSOR | eBay

BOYU Water Level High Low Alarm Fish Tank Aquarium SW01- UK SELLER | eBay

Thanks BT, I'd never have found those...

They looked like they'd do the job, untill I got some more info'. Tests on a Bora showed resistance oof 500k and on an Audi A1 of 900k ohms. so there's seems to be a huge variation.

Seeing the range of readings I wonder how high the resistance has to get before it one of those wouldn't trigger and how high it gets on the sensor when the level is low (No reading have been posible on an empty one). For now I've disconnected it all while I think about it. Not had a working/reliable sensor for the last 5 years so not a huge problem.

I might just re-assign the LED to be fan override on; I keep putting that on then forgetting to switch it off. Atleast in that role I'd know it was flashing for a reason.

Have you put the fancy engine in Adi?

On the coolant issue. I had a series of MK2 GTi Golfs and had several new bottles flash the light when the engine was hot but were fine the rest of the time. I never did get to the bottom of that.

quote:

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Originally posted by rdodger
Have you put the fancy engine in Adi?

On the coolant issue. I had a series of MK2 GTi Golfs and had several new bottles flash the light when the engine was hot but were fine the rest of the time. I never did get to the bottom of that.

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