B3 Passat/mk2 golf? Coolant warning light sensor.

[Dez]

I have a b3 Passat. 1993 1.8 8v single point injection.

The coolant light randomly flashes. Sometimes it does it, some times it doesn't. Can do it hot or cold. Gauge always stays in 90-100deg zone and the car had no signs of overheating so I'm putting it down to the sensor for the flashy light being duff. So can anyone tell me which sensor it is before I have to go chasing it?

[Deleted]

One in top of the coolant expansion bottle. Normally it's water in the relay under the dash. If memory is correct,it's relay 42. Very seldom the sensor in the bottle. If you do remove the sensor,only tighten it with a socket, no ratchet. Hand tight or it cracks through the o ring groove when it warms up. Replace the relay,it's got electronic gubbins inside a relay casing. Job done 😊

[Dez]

Next dumb question. Where the hell is relay 42? Finally got round to doing something about this and just assumed it would be on the relay board under the dash, but it’s not...

[duggers]

I've also had an issue in the past with aged wiring at the connection on the header Tank (bottle) if its that type. Its a level sensor that screws into the header tank and when old can be a bit fickle as the wiring gets brittle or the sensor itself packs up.

[Deleted]

Dez,I am not sure on the Passat location. What I can tell you,is when you open it up,it's a printed circuit board with a smaller relay soldered onto it. Your best bet might be to have a listen when the light is flashing,you should be able to hear the relay. I think it also flashes the light once or twice when you switch the ignition on. I would have thought it would be integral to the fuse box.Sorry it's not more help,but it's a good 20 years since I played with one 😂