The coolant in my truck keeps disappearing. They have checked the radiator and the resevoir under pressure and there are no leaks. The thermostat and radiator cap have been replaced. The mechanic can't find a leak, yet the coolant keeps just going away. There are no leakage stains on the pavement where I park every day so it has now become a mystery as to where is the coolant going. What would you suggest checking next, I am assuming that there is a leak, but where? I appreciate your helping me out with this if you can. Thanks