Mercedes Benz ML350 Coolant Reservoir Problems and Solution
The Mercedes Benz ML350 coolant reservoir level must reach the coolant marker or the filter neck when cold. If the engine is warm, the coolant rises slightly, about half an inch. This should be your guide when checking if you have enough coolant in your system. For other problems, refer to the information below:
Leak in the coolant reservoir
There are many places where the coolant may leak (water pump, freeze plugs, hoses, radiator, intake manifold gaskets, heater core, and coolant reservoir). Each has a way to fix the problem. If the leak is in the coolant reservoir, you may opt for repair. If the coolant reservoir is cracked or has small punctures, the cooling system may lose the fluid every time your engine heats up. Left unchecked, there will not be enough coolant to keep the temperature of the engine and may result to overheating. Patching the leak with silicone glue may be a quick solution, but if your reservoir is relatively old and on its way out, replacing it is a better option.
There are several causes of overheating. If the issue is with the coolant level, check the coolant in the reservoir and fill if necessary. If there is an adequate amount of liquid in the reservoir, check other parts of the cooling system if they are operating correctly: cooling fan, fan relay, and thermofan switch. Check the head gasket if it is leaking and check if you have a bad water pump.
Steaming reservoir or boiling coolant
If you notice steam coming out of your coolant reservoir or the coolant inside is boiling, do not do anything without allowing it to cool down. The problem may be caused by a low coolant level in the reservoir or inability of the reservoir to maintain correct pressure. Fill the reservoir with coolant if necessary. If you have a coolant pressure tester or can borrow one, use it. Refer to the figure stamped on the cap. Make sure that the reading doesn't fall significantly lower than what the figure on the cap indicates.