Hi there - new here and just about to get my 1988 8V Mk2 Campaign back from panel workshop after buying her a few months ago but was going to get it serviced before it comes back to me. I've heard a lot about flashing coolant lights and mine also flashes quickly (at least it did when I drove it the two times aftre buying it) but am not sure if it's a simple fix and whether i should but a new thermostat/switch etc - any thoughts from anyone, part number or brand - it's a standard 8V GTI.
Flashing is usually level if it does it from the off, the sensor gets gunked up in the bottle you can clean it or the wiring to the sensor is dodgy.
AS above get a new sender.sensor, probably... and top up with fresh coolant to ensure conductivity through the coolant so sender works. check for water passing through system.. if not, remove water pump and flush , maybe blockages..
If your water level is good disconnect the plug from level sensor, and it shouldn't flash. If still flashing and engine cold then either wiring (unusual, not unknown) or temp sensor faulty (black sensor I believe) again you should be able to disconnect and should stop.
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You can bridge pins on either connector to test wiring for that circuit.
I had this once in the early type expansion bottle that you car will have. It was actually some water sitting in the top of the bottom in the indentation where the sensor goes.