1988 C4 Drained cooling system,new anti freeze + distilled water. Now low cooling light Any ideas?keeps coming off and on. All levels correct. Any ideas?

 

Welcome to the forum. While I don't know how they sense the level, I would try to determine if the sensor itself is working. If it is, then I would make sure that all of the air has been removed from the system.

 

Welcome, It does seem rather odd the light comes on after a service. Is there a possibility you bumped the sensor or the wiring at the sensor creating a bad connection? Sensor may be cracked or broken or corroded. There is a module in that system also. If you pull the sensor out and test it make sure the probe is clean.