Club 80-90 Forums

I want to find out if I can wire up something to act as the water level indicator that bypasses the relay 43. The temperature gauge works but after the starting routine the light flashes constantly. When I take out the relay the light goes out. I have replaced the water level sensor, the old one was cracked and leaking into the connection and probably shorted them out, possibly damaging part of the relay?
Since the head gasket blew and I had it replaced, I have replaced the radiator, the filler cap and the earth from the sensor is good. I still have problems with the water level fluctuating and as I have no idea how to stabilise the coolant level, so it doesn’t overflow or run out, I need a reliable way to know I have sufficient coolant. I think it would make sense to have an indicator that was independent of the frail foil circuits behind the dash. From the Wiki pages it would seem that the sensor is more than just a continuity indicator and sends an electronic signal to the relay.

Welcome to the forum chap

Did you read this?
https://club8090.co.uk/wiki/Co ... alfunction" onclick="window.open(this.href);return false;

Thanks but the temperature gauge is working fine it is only the coolant level function that is causing a problem.
Do you know if the coolant sensor has a positive and negative terminals?
The old one had a shaped hole for the connector and it would only go in one way, the replacement has a rectangular hole and the lead can plug in either way around.
A wiki page mentions that the sensor sends a pulse signal to the relay which would suggest that there is a right way and wrong way to connect it. There don't seem to be any markings on the connections on the sensor.
Do you think it worth the expense of buying a replacement relay 43, I wouldn't want to risk frying a new relay because I got the sensor connected to it the wrong way round?

If you connect the two pins of the plug to the coolant level sender together, does the flashing light stop ?
It much more likely to be a wire issue between the sender and the relay rather than the relay in your experience

No connecting the probe ends together makes no difference.
As you say there is a good chance that it is a wiring fault, that is why I think that bypassing it and making a separate indicator might be best.
As I said before I think that the sensor is more than just an extension of the wires into the coolant and includes some electronics, though I can't see where it would fit.

No electronics, just two probes to make/break the circuit. The pulse is sent by the electronics (relay size box not a basic relay as such) not the probes.

Thanks, I'll see if I can test for continuity between the probe and the relay 43. On the circuit diagram on the wiki page it look as though the lead from the probe is marked S. If that connection is good is it reasonable to presume it is the relay 43 and replace it?

Thank you for your advice, I tested the continuity from the sensor to the socket of the 43 relay and it was good. I called Vlokspares to check if they had a replacement relay, which they did and set off to get it. Well blow me down, the problem seems sorted. I disconnected the sensor to check that the light would come on again, which it did and replaced it, tested with the engine running and after the start up routine the light went out. Finished my trip to Volkspares to check it was working once the engine was up to temp and all seems to be well. So the problem seems to have been an intermittent connection to the relay as you said. Possibly checking the connection to the socket cleaned the terminal?
Thank you Club 80-90 for your calm advice.

Well done! If the original relay was testing ok it could have just been a cruddy connection that was solved with the clean pins on the new relay. Were the old ones particularly dirty out of interest?


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I'm afraid that it isn't good news. I took the bus out for a run and it was fine on the way out but as soon as I started back the light flashed on again. I checked the water level which was fine and took out relay 43 and connectors were bright. Put it back and the light continued to flash all the way home.
What to do now as it is obviously an intermittent fault? It could be the the lead from the gauge to the socket or the relay. I don't really want to lay out on a new relay, to find that makes no difference and I'm not keen to pull the fuse panel about to put an alternative lead from the gauge. Is there a sensible way to tackle this?

My "relay" (42 but interchangeable with 43) had a bad connection inside, where the spade connectors joined onto the pcb. Caused intermittent flashing light. Fixed by resoldering. Well worth trying another relay, usually some on ebay, eg

http://www.ebay.co.uk/itm/311628469780" onclick="window.open(this.href);return false;

Have you check and brightened your earths underneath the dash (just above the fuse box to the left). There's two earth crowns there that often get quite corroded. That would definitely explain your symptoms.


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Thanks for the advice, I afraid I've been away hence no reply. I'll have a go and let you know.

Hi Martin. Sorry in advance that this comment won't help you, but I have a similar issue and was wondering if it was easy to change the sensor in the tank. I'm pretty sure mine is leaking as the connector is often wet inside the rubber housing even after I've dried it! Although I can see from your experience that the flashing light may have a different cause I'd like to start with the sensor!

Did u get it from Vw or elsewhere?

Hi there really sorry not to have got back to you sooner. We have been in Germany visiting our daughter not in the bus, I'm afraid. I got my water sensor from Volkspares in Sydenham http://www.volkspares.co.uk" onclick="window.open(this.href);return false;

My sensor issues are solved but I'm having to bleed the rad all the time. I'm worried that I have a leaky head gasket, I just logged in to submit a new question about it.

Good luck
Martin