The sensor is not by the side of the radiator, that is the temperature sensor that turns on the electric fans when the temp gets too high. These fans also turn on to cool the condenser when the A/C is turned on. If you don't have A/C you wouldn't have the fans but may still have the temp switch in the side of the radiator. I believe new radiators are only available with temp switch for A/C compatibility.
As Howard says the coolant light is turned on by sensor in the brass expansion tank as found on the later LH tanks were it was moved to make way for the air cleaner/air mass meter on the RH side found on FI cars and was used on carb cars for compatibility sake. It measures coolant depth (not mixture) as it is critical so the engine doesn't over heat due to not enough coolant and warp the head. Normal coolant height is about second knuckle of finger down from top of filler hole. The rest of room in tank is for coolant expansion as it warms up and expands. If you have too much coolant it will harmlessly go out the overflow tube except for the mess it makes on the garage floor (and resultant danger to pets) when you turn the engine off and you get that last bit of expansion from the heat spike when it stops circulating. If you have to keep adding coolant it may be that the system is expelling air in the system (as when you change coolant) or it is leaking. That may be from the radiator (leaving tell tale signs of blue/green residue), from the hoses (either cracked or loose clamps) or (commonly) from the failed seal in the water pump where it gets passed and leaks out the rectangular hole on the left side of the block below the intake manifold leaving a tell tale sign of leakage or on no longer painted engines a rust trail down. This necessitates removing intake manifold and pulling the pump to replace seal/bearing and gaskets in a rebuild kit and/or pump. Much has been written on that subject and must be read before attempting it, many of us have done it, not me (yet). Don't leave it to a mechanic not familiar with the slant 4 engine as it will be buggered up by him if not done right.
- - -TR7 Spider - - - 1978 Spitfire- - - - 1976 Spitfire - - 1988 Tercel 4X4 - Kali on Integra - 1991 Integra - Yellow TCT
