The rise and fall of the level of the coolant levels in the reservoir bottle is in sync with the rise and fall of the coolant temperature as it varies between hot and cold. It is perfectly normal for the level to be under the “max” level indicated on the reservoir bottle when the engine is hot. Because liquids contract when cold, the cooling liquid will flow back into the cooling system, so the fluid level in the coolant bottle will rise. The opposite will happen when the engine is hot. You can make this comparison yourself after having your car parked over a long period of time and shortly after having driven it for some time. If you fill the reservoir bottle with coolant when the engine is cold, when it becomes hot it will overflow out of the bottle, thereby dropping the coolant level in it, and you might think the vehicle is losing fluid when in fact it is not. Refrain from filling the reservoir bottle past the “max” line and under no circumstances should you open the radiator cover when the engine is hot. The cooling system is highly pressurized when it is at maximum temperature and can cause severe injuries if you open the radiator after operating the vehicle. If the case is the coolant is being lost completely when the engine is running without a sign of a leak report it to your dealer or mechanic to solve the problem.
By: Taj Stewart