Radiator light blinks on 92 Jetta EcoDiesel

Low coolant level.

Check the coolant tank, it might be a tad low.

And the sensor is a bit touchy. On my own '92 ECOdiesel, if the coolant level is just a bit low, the warning light will start blinking a few seconds after I start the engine for the first time in the day. But if I turn the ignition off and then on again (even while moving in gear so I don't have to re-crank it), the light will go off and stay off, even though the coolant level is no different than before.

I agree with the others...low coolant level. Once triggered it stays on until you turn the car off and on again and it's being triggered when the coolant sloshes to one side of the tank. Eventually it'll be low enough to be triggered all the time unless you top it up to the "max" mark.