What is causing my Mercedes Classe M to overheat ?

What should you do if the engine of your M Class overheats?

If the engine overheats, your M Class will turn on the following warning light:

If the warning light of your M Class comes on, or you see that there is steam coming out of the car’s hood (or bonnet), you should follow these precautions for both your safety and your car’s safety:

If the temperature is high but there is NO steam coming out of the hood:

  • Stop your car in a safe place and do not turn your car off so that the refrigeration system keeps on working.
  • Wait with your engine at idle speed until its temperature drops and the light goes out. Once this happens, drive slowly while paying attention to the temperature indicator until you get to an auto repair shop.
  • If the temperature does not drop, turn the engine off and phone your preferred tow truck.

If there is steam coming out of the hood:

⚠️ Turn your car off and get away from it. Do not try to open its hood, this steam flows at high temperatures and it may be dangerous to stay close to it. Let it cool down on its own.

⚠️ Call your insurance company so that a tow truck can come for your car.

⚠️ After such an incident, it is probable that your engine has been damaged and will not work anymore. You should have a specialist check it out if that is the case.

⚠️ Under no circumstances should you open the hood or the coolant reservoir. If you do that, the liquid may be ejected upwards, and you may get burned.

What kind of coolant should you use in your M Class?

There are a lot of different types and brands of coolants, and each one has its particular characteristics. You should always use the kind of coolant indicated in the owner’s manual. Like this, your M Class‘s engine will be thoroughly protected. If there is an emergency, you can use a coolant with glycol, no matter their color (they may be either green or pink). Afterward, when you have time, you can check the specific type of coolant your car needs.

How do I prevent my M Class from overheating?

There are some overheating causes that you can easily prevent yourself:

— Always use high-quality coolants: change the coolant every 30,000 miles (50,000 kilometers) or after 2 years. If you want to know more about this, you should read the owner’s manual.

— Never use water (either distilled or tap water): the coolant has certain qualities that are very important for the correct performance of the system. For example, it boils at a higher temperature.

— Check the coolant level every 15 days: keep the coolant level up to the level indicated in the coolant reservoir.

— Clean the radiator fins: the radiator may gather some garbage such as leaves, mud, or dust that clogs its airflow and its cooling qualities will decrease. Clean it with a brush every time you check the coolant level.

Why does my M Class‘s engine overheat?

There are two main causes for engine overheat:

  1. The coolant does not flow through the system like it should
  2. There is not enough air flowing through the radiator

⚠️ The coolant does not flow through the system like it should. These may be some of the causes:

  • Not enough coolant: check the coolant level periodically. If the level is under the minimum level recommended, the engine may overheat because there is not enough coolant.
  • The pump may be worn out: it is advisable to change the pump every time you change the timing belt, since there is an excellent cost-benefit relationship.
  • Clogged radiator: the internal tubes are small and, as time goes on, if the coolant is not refilled periodically, dirt accumulates and blocks these ducts.
  • Clogged engine ducts: just like the previous item, but in the internal engine ducts.
  • Unresponsive thermostat: thermostats usually become unresponsive because of the dirt, which prevents the coolant from getting to the radiator.

⚠️ There is not enough air flowing through the radiator. These may be some of the reasons:

  • Clogged radiator fins: the radiator may gather some garbage such as leaves, mud, or dust that clogs its air flow and its cooling qualities will decrease.
  • Bent radiator fins: if you are not careful, you do not handle them carefully, or pressure-wash them, the fins will get bet until they block most of the airflow.
  • The electric fan does not work: the electric fan might be damaged. If the temperature sensor or the control module are damaged, it may also stop working.
  • Poor-quality coolant: you should always use the coolant recommended in the owner’s manual, and renew it after the specified time period, which is usually every 5 years.
  • Broken or loose radiator or reservoir cap: the cooling circuit must work while it is under pressure. If the caps are damaged or loose, this pressure and the liquid will leak.
  • Not enough lubricant: when the friction between the internal pieces increase, the temperature and the wear increase significantly, and this may cause severe damages if it is not fixed on time.
  • The cylinder heads may be broken: the combustion gases get into the refrigeration system, and this will increase the temperature and form gas bubbles.

How does the system that cools the engine of your M Class work?

All engines have a cooling system, which works by taking the heat from the engine to the radiator.

This system is quite simple, and it includes the following parts:

  • Coolant
  • Radiator
  • Coolant pump
  • Temperature sensor
  • Thermostat
  • Electric fan

The engine cools thanks to the coolant, or “antifreeze.” You can usually buy it at gas stations when you “check the fluids.” It is typically green or pink. You must never use just water; this will damage the engine in a very short time period.

You can see how this system works in the following image: the liquid takes the heat generated by the engine and takes it to the radiator. There is a pump that makes the liquid flow, and it pushes it along the circuit. The hot liquid enters through the upper part of the radiator, and it comes out being cool from the bottom part.

In order to keep its good performance, the engine of your M Class must always stay within the optimal temperature range, which is usually around 190ºF (90°C). To guarantee this temperature, the system has two “auxiliary” pieces that control temperatures: the thermostat and the electric fan. The thermostat prevents the coolant from cooling too much, and the electric fan stops it from heating.

The temperature sensor monitors the whole system that is usually controlled by the central computer or by a separate electronic module, depending on the car manufacturer.

Like in every system, any of these parts may malfunction or get damaged, and that will make the engine overheat, as we explained above.

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