The flashing light is the "low coolant level warning light".

You have two water tanks in the coolant system. They are in the engine compartment. There is the coolant expansion tank, and the coolant overflow tank. The expansion tank is an active part of the system and when the engine is running coolant circulates through expansion tank. In the top of the tank is a sensor with two electrodes or prongs that stick down into the coolant. As long ast the coolant is above the tips of the electrodes, a tiny current can pass between them, keeping the LED light on the dash in the "off" mode. If the coolant gets low, the circuit is broken, and the light comes on blinking, telling you to add or at least check the coolant level.

As a self test, the light comes on at engine start, will blink for a time and then go out. That is proper operation of the light. On occasion the LED will come on during driving. If the coolant is very hot, the light  comes on, and it will come on if the coolant/water mix is not 50/50. And it will come on if there happens to be a little trash caught on one of the electrodes.

The coolant system is a closed system, and includes the expansion tank. As the coolant warms up it expands. The expanding coolant must go somewhere, so the pressure cap on the expansion tank opens, and vents coolant into the overflow tank. Once the engine is off and is cooling down, the coolant shrinks, a suction occurs, and the coolant is drawn back into the expansion tank.

I have found that replacing the sensor and the thermostat every year contributes to good health of the cooling system.

Hope this helps.

John Rodgers
"88 GL Driver

Andrew Grebneff wrote:

I've never been able to work out what the flashing red LED in my 84
Caravelle's instrument cluster is for. It starts flashing on startup, and
goes out some time later. A couple of times it's come back on while
driving, but doesn't seem to be warning of high coolant temperature.

What IS this LED for? I don't have a owner's manual and that paragon of
incompleteness the Bentley manual doesn't mention it.

Andrew