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Mercedes Benz ML350 Coolant Reservoir

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.

Engine overheats

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.

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  • Mercedes Benz Ml350 Coolant Reservoir Maintenance Guide 27 February 2013

    Since it is a part of the cooling system, it is important that you follow strict guidelines on how to maintain your coolant reservoir as well as the fluid that goes into it. Here are the things you need to do in order to keep your engine from overheating and to keep the water from your car from freezing:


    Do not overfill the reservoir.


    The coolant reservoir also acts as (and called) "overflow tank" of your radiator. Because the liquid in the radiator expands when it gets hot, the radiator pushes this liquid out through the hose and into the coolant reservoir. If the coolant reservoir is overfilled, the expanded liquid will have nowhere to go. In worst cases, the pressure may damage the radiator or may cause leak to the hose. Fill the coolant reservoir up to the "MAX" line and do not let the coolant level go below the "MIN" line.


    Flush out your cooling system as recommended by your manufacturer.


    Some recommend that you should flush your cooling system once every 3 years, while some say that it is every 5 years. To be sure, refer to your owner's manual to know how often you should change you should flush out your cooling system. Still, your location will affect how long you have to change your cooling system.


    Check the overall condition of your coolant reservoir.


    While the coolant reservoir is made of high-quality plastic, temperature under the hood and the pressure of the liquid from the radiator can cause it to leak. Whenever you fill or flush your cooling system or whenever you check your radiator, take time to inspect your coolant reservoir as well as the clamps and hoses.


    Dispose your fluid properly.


    Although technically, this is not related to the reservoir, it is good that you know what to do with that liquid after you have flushed it out. The coolant liquid is toxic and can harm your pet and your kids. Contain the coolant carefully. Take it to a hazardous waste facility. The water that is used to flush the coolant out should be captured as well. Do not let any liquid go into the sewer.