The coolant light comes on now occaisionally on my 1992 300E 4-matic. It's very dim, not really the full strength light you see at start up. But the coolant level is fine and the engine isn't overheating. Any ideas? I did recently have the coolant replaced at a Quick Lube kind of place and they put in a very green-looking liquid, opposed to what came out – which was much more clear. Is the type of coolant important and does using different types make a real difference to cooling efficiency?