Resently I've notised the antifreeze level starts to go down, not too much, about a quarter in a week. I took the car to mechanic to solve the problem, because I couldn't see myself any leak under the engine or on radiator and hoses. the mechanic had a special tool to pump the pressure of air into the system to spot the leak, the pressure slowly went down, but there was no leak outside, the antifreeze doesn't go in the oil, because it didn't change the color, didn't go in the chambers too, there was no steam in the exhaust.