Volvo Repair: Radiator Light- 1993, temp gauge, new sensor

Question
Hello,
I have a 1993 850 Volvo GLT. Just about 3 years ago my car overheated and the thermostat was changed.  Last year my lower hose broke and I lost all my coolant. I had a very small leak prior to total lost.  Coolant flushed and hose replaced.  

Now, my radiator light on the dash is coming on sometimes after car has been driving for a while.(I can drive 30 or so miles and the light never come on or it can come on...3 week problem)  The temp gauge does not go up to indicate overheating.  As a matter of fact the gauge is a little lower than it has always been.  The light does go off once the car has sat for an hour or so.  It has been in the 50s temp wise for us and very humid as weather is concerned.

Any ideas as to what is causing this light to come on.  Thanks for your help.  

Answer
the light is for low fluid level.it could be a bad low level sensor.it could be the sensor heating up causing a problem I would check the level in the resevoir next time it coes on.if it is ok I would try a new sensor.it could also be a bad float in the resevoir.