I have a 1998 Mercury Mystique GS. Where is the Coolant Level Sensor located ? My radiator low light intermittently comes on and goes off within 2 minutes of starting up and driving. I've checked the coolant level and it is full, temperature gage is normal, no antifreeze leaks under the car. I'm thinking I have a bad sensor. How expensive is it to replace? Today, driving to work it stayed on constantly - about a 20 mile commute. Already Tried: Checked coolant level, it was full. Topped off coolant level and slightly overfilled it. Checked for hose leaks - none. Checked under car for leaks - none. Replaced upper radiator hose a year ago so am not worried about circulation problem. Temperature gage is normal and engine doesn't run hot.
The Coolant level Sensor is located in the overflow tank. Look for the electrical wires and there it is. You may just be able to add some coolant to the overflow tank to take care of the issue. It does not read the radiator level, just the overflow level. If you need to have it replaced, it should cost under $100.00 parts and labor.
When the fluid in the cooling system heats up, it expands, causing the pressure to build up. The cap is the only place where this pressure can escape, so the setting of the spring on the cap determines the maximum pressure in the cooling system. When the pressure reaches 15 psi, the pressure pushes the valve open, allowing coolant to escape from the cooling system. This coolant flows through the overflow tube into the bottom of the overflow tank. This arrangement keeps air out of the system. When the radiator cools back down, a vacuum is created in the cooling system that pulls open another spring loaded valve, sucking water back in from the bottom of the overflow tank to replace the water that was expelled.