Can a Mercedes Benz Overheat?

This blog will take a look at the cooling system in Mercedes Benz cars and answer the following questions: can a Mercedes Benz overheat? When does a Mercedes Benz overheat? What to do if your Mercedes Benz car is overheating?

Can a Mercedes Benz overheat?

Yes, a Mercedes Benz can overheat like any other car running on an internal combustion engine. Mercedes Benz cars have more than one coolant reservoir and auxiliary water pumps that circulate the coolant in the engine and various heat exchangers. The hot coolant is supplied to the radiator on the top side and as the air flows over the radiator fins, the coolant temperature goes down. Thus the coolant is ready to be circulated in the coolant circuits.

When does a Mercedes Benz overheat?

A Mercedes Benz can overheat under the following situations:

• Low coolant level

The coolant in a Mercedes Benz car consists of different concentrations of water and antifreeze. In hot countries, the anti-freeze liquid is replaced by an anti-corrosion liquid. The coolant level is monitored by a coolant level sensor but if the customer ignores the warning and continues to drive the vehicle; the level eventually goes down. As the water in the coolant evaporates, its heat carrying capacity is also reduced. The engine and critical components like cylinder head gasket and rubber O-ring are designed to function only at the operating temperature of the engine. As the required quantity of coolant is no longer circulated in the engines, the vehicle starts to overheat and there is permanent damage to the cylinder head gasket and o-rings.

• Leak in the coolant system

The coolant system in the Mercedes Benz car is pressurised and the cap in the coolant expansion also contains a pressure relief valve. However, leaks can develop in the coolant system near coolant hoses and water pump gaskets over time. 

A coolant leak test is performed at authorised dealerships, it consists of a pressure tester and coolant expansion reservoir cap. The pressure tester is connected to the coolant expansion reservoir and the complete coolant system is pressurised. If the pressure in the coolant system falls below 1.4 bar then a visual inspection is carried out to identify the coolant leak. The coolant also leaves marks on the engines when it is dried up. This is also a good indication of a leak in the system. If the coolant leak is not rectified then the coolant level will go down depending on the size of the leak.

• Faulty water pump

Mercedes Benz uses mechanical as well as electrical water pumps in almost all of the latest engines. The water pumps are regulated with the help of electro-pneumatic transducers in the case of mechanical water pumps and a powertrain control unit actuates the electric water pump as needed based on the coolant temperature sensor. Therefore the coolant temperature sensor is very crucial for the cooling system of the vehicle. The engine control unit is constantly monitoring the coolant temperature as it can even reduce the engine speed if the temperature is rising too quickly. 

The fail-safe system built into the electronic control unit is not effective if the water pump itself stops pumping water from the engine block to the radiator. A faulty water pump causes the coolant to evaporate in the engine block and the vehicle overheats. Replacing the faulty water pump is the only remedy. The engines with electric water pumps can directly generate a fault code and continue to run in limp home mode until the ignition is turned off.

• Stuck / partially stuck Thermostat

Mercedes Benz cars use a thermostat with an electric heating element to control the opening of the valve inside the thermostat. A thermostat is installed between the engine block and the radiator, it controls the amount of coolant being sent to the radiator. The engine control unit actuates the heating element connected to the valve. However, if a thermostat does not completely open or it is stuck in partial condition then the vehicle will overheat as adequate coolant is not being circulated in the coolant system.

• Blocked Radiator or faulty Fan

An electric fan is located on the radiator in Mercedes Benz cars, it is tasked with cooling the radiator and condenser. As the airflow over the radiator is not constant because of different driving speeds; the electric radiator fan can operate at variable speeds so that the operating temperature is constantly maintained.

A faulty electric fan can restrict the airflow over the radiator leading to overheating issues. Similarly, a radiator can get blocked due to dust and insects which lowers its performance. The electric fan communicates with the powertrain control unit over the LIN signal and if there are any malfunctions then a fault code is stored in the DTC memory. 

The fan bearing can also get damaged due to the dust and it will cause excessive vibrations and noise when the fan is running. Always ensure the fan is off before performing any visual inspection as pieces of loose clothing can get caught in the rotating fan and cause injury. 

 What to do if your Mercedes Benz car is overheating? 

If your Mercedes Benz car is overheating there will be an overheating warning message in the instrument cluster. The coolant temperature gauge will also show 120-degree celsius reading instead of the ideal 80-90 degrees. Perform the following steps to prevent damage due to overheating of the engine.

• Find a safe stop and pull over to the side of the road immediately.
• Open the engine hood so that hot air will escape more easily.
• The radiator fan will be running at full speed so care should be taken after opening the engine hood.
• Turn off the engine and let the radiator fan run, in some cases the battery might drain. Hence do not use any interior types of equipment like blower motors or lights.
• After the temperature goes down the radiator fan will turn off, and perform a quick visual inspection of the engine compartment.
• If there are signs of a coolant then tow the vehicle to the nearest workshop.

Mercedes Benz workshops are equipped with all the tools required to diagnose a coolant leak and rectify it so that it does not occur. It is always a good practice to check the coolant level before starting a long journey. 

Important note: Never open the coolant expansion reservoir cap when the coolant is hot, there can be injuries

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as the hot coolant will escape the reservoir and come in contact with the skin causing burns. 

Conclusion

Mercedes Benz has designed multiple fail-safe systems so that the vehicle won’t overheat but the fail-safe systems only work when the rest of the cooling system is functioning properly. Overheating of the vehicle can easily be prevented by checking the coolant level and coolant concentration as specified by the manufacturer.