Cooling system for MAN / Mercedes trucks, buses and vans

The cooling system is essential to the reliability and service life of every MAN or Mercedes truck, coach and van. Internal combustion engines deliver high performance under heavy load, but that performance comes with significant heat generation. The cooling system ensures that this heat is dissipated in a controlled way, so the engine and related components continue to operate within safe temperature limits. When the cooling system does not function correctly, severe engine damage and unexpected downtime quickly occur. At Braem you will find an extensive range of cooling parts that enable maintenance and repairs to be carried out professionally and sustainably.

The function of the cooling system within the vehicle

The cooling system regulates the engine’s operating temperature by removing the heat produced by combustion. Otherwise, this heat would damage the engine through overheating. Combustion in the cylinders generates high temperatures. Without cooling, components such as the cylinder head, the pistons, the crankshaft and the engine block can deform. At excessively high operating temperatures, engine oil loses its lubricating properties, which can cause the engine to seize. An engine that seizes is severely damaged and is often beyond repair.

Interaction with the engine and the heating in the cab

Heat exchange is the process in which thermal energy is transferred from a body or medium at a higher temperature to a body or medium at a lower temperature, until thermal equilibrium is reached. Technically, this can occur via three mechanisms. Through conduction, heat is transported through a material via direct contact. A metal rod heated on one side conducts this heat to the other side of the rod until the rod’s temperature becomes uniform. Heat exchange can also occur through convection. Here, heat is transferred by a flowing medium such as a liquid or a gas. A third method is radiation. Here, heat is transferred via electromagnetic waves. It requires no contact or medium. The energy is transmitted directly through space. The sun is the best example of this. In summary, we can say that heat always flows from a higher to a lower temperature. The heat transfer capacity depends on the temperature difference, the type and surface area of the material, and the properties of the medium. An engine cooling system mainly uses conduction and convection to transfer heat, with a small amount of radiation.

Conduction: The engine block is equipped with cooling channels through which coolant can flow. The water pump mounted on the engine block pumps the coolant through the cooling channels, transferring heat from the hot engine components to the coolant. The engine therefore cools down. This is a transfer of heat through direct contact between the metal surfaces and the coolant.

Convection: The heated coolant is pumped by the water pump via coolant hoses and lines to the coolant radiator. This radiator is mounted in the vehicle in front of the engine. When the vehicle is driving, air from the atmosphere is pushed against the radiator by the direction of travel. This air flows along thin cooling fins and thin metal tubes that make up the radiator and absorbs the heat from the coolant coming from the engine. As a result, the heat from the coolant is absorbed by the airflow, cooling the coolant. This cooled coolant is pumped back to the engine via the water pump and lines, allowing the conduction process explained above to start again.

Radiation: To a lesser extent, heated engine components radiate heat into the surroundings through their surface area. This radiation plays a small role compared with conduction and convection.

Water expands when heated, so it takes up more space. The expansion tank mounted on top of the radiator absorbs the expansion and contraction of the coolant during temperature changes, keeping the pressure in the cooling system safe and constant.

The cab heater mainly works on the principle of convection. Warm coolant coming from the engine is routed via lines that are part of the engine’s coolant circuit, by the same water pump, to the heater core. Outside air is drawn in by the heater motor (which is actually a fan) through a cabin filter that purifies the outside air and is forced through the heater core. The coolant transfers its heat to this air, which is then blown into the cab. This increases the temperature in the cab. To make this temperature controllable, a heater control valve is installed in the coolant circuit. This is controlled by the control system in the cab. The heater control valve thus determines the required flow rate of warm coolant needed to achieve the requested temperature.

Main components of the charge air cooling system and A/C system

The principle of heat exchange is also used in 2 other processes.

The charge air system and its influence on engine power

By compressing the mixture, the fuel ignites due to the high temperature of the compressed air during the engine’s power stroke. The power of the engine depends on the amount of fuel you can burn in a given time. The more air there is in the cylinders, the more fuel can effectively be burned. The volumetric efficiency indicates how much air enters the cylinders compared to the maximum volume. If we can increase this volumetric efficiency, we can boost engine power. The compressing action of the turbo increases the volumetric efficiency. To optimize this volumetric efficiency even further, the air coming from the turbo is cooled by the intercooler. Air that is cooled shrinks in volume. As a result, more air can and does enter the cylinders. The intake air coming from the air filter housing is compressed by the turbo and is forced via charge air pipes to the intercooler. This intercooler is mounted in front of the coolant radiator. When the vehicle is driving, air from the atmosphere is pushed against the intercooler by the direction of travel. This air flows along thin cooling fins and thin metal tubes that make up the intercooler and absorbs the heat from the air coming from the turbo. After cooling, the air is transported via pipes and flex hoses to the intake manifold, from where it flows into the engine cylinders.

The A/C system is a cooling system for air, in which heat is moved from the cab to the outside air.

A/C cooling works according to the principle of heat transfer and phase transitions of the refrigerant. The system transfers energy from a warmer zone (the cab) to a cooler zone (the outside air) via a closed refrigerant circuit. An A/C compressor compresses the refrigerant gas, increasing its pressure and temperature. Due to pressure differences, the refrigerant moves via A/C lines to the condenser, which is mounted at the front of the vehicle in front of the intercooler. When the vehicle is driving, air from the atmosphere is pushed against the condenser by the direction of travel. This air flows along thin cooling fins and thin metal tubes that make up the condenser and absorbs the heat from the hot compressed refrigerant gas. This causes the refrigerant gas to condense into a liquid. An expansion valve then installed in the refrigerant circuit ensures that the pressure and temperature of the refrigerant drop sharply. This refrigerant flows to the evaporator, which is mounted against or in the cab. The heater motor (fan) forces warm air present in the cab straight through the evaporator, allowing the refrigerant circulating inside it to absorb the heat and evaporate into a gas. As a result, the temperature in the cab drops. The low-pressure gas flows back to the A/C compressor and the cycle can start again.

Coolant radiator https://www.braem.com/nl/vrachtwagen-onderdelen/koelsysteem/koelvloeistof-radiator/koelvloeistof-radiator, intercooler https://www.braem.com/nl/vrachtwagen-onderdelen/koelsysteem/intercooler/intercooler, condenser https://www.braem.com/nl/vrachtwagen-onderdelen/koelsysteem/airco-systeem/condensor and airflows

For proper operation of the coolant radiator, the intercooler and the condenser, air must flow through them crosswise. When a vehicle is driving at a certain speed, this happens automatically. However, when the vehicle is driving too slowly or idling, the airflow is insufficient to cool the engine adequately. The engine’s volumetric efficiency drops, meaning the requested power can no longer be guaranteed. The A/C system does not work optimally. In that case, a second airflow is generated by a fan mounted between the coolant radiator and the engine, which, when operating, forces air through the heat exchangers. On truck engines this is usually mounted on the engine via a viscous coupling. This slip coupling regulates the fan speed depending on the need for cooling. A fan shroud mounted on the back of the coolant radiator guides the air into the engine compartment.

Common wear and recognizable issues in the different cooling systems

Engine cooling

Poorly functioning engine cooling can cause the engine to overheat or seize. The coolant radiator can become clogged, lose coolant due to leaks, and rust. Dust and sand carried by airflow can clog the radiator. Connecting hoses and lines can crack and harden, causing the sealing to no longer be adequate. Fans can deform due to engine heat. A viscous coupling can lose its fluid or be internally worn.

Charge air system

The intercooler core shows cracks, leaks and rust. Intercooler hoses and lines leak. Dust and sand carried by airflow can clog the intercooler.

A/C system

The A/C compressor is a pump with bearings. It is subject to wear and overload. Dust and sand carried by airflow can contaminate the condenser. Due to condensation issues, the evaporator can rust. A/C hoses and lines leak.

Overall wear

All cooling parts are subject to vibration damage. Due to continuous expansion from heating or contraction from cooling, components are subject to thermal fatigue. This causes cracks and fractures. Airflow causes mud, sand and other contaminants to foul the heat exchangers, causing them to clog and lose efficiency.

Typical warning signs of poorly functioning processes

Many parameters of the different cooling systems are measured by sensors. The results are visible on the dashboard via warning lights. In the event of engine overheating, the temperature gauge rises too high and the warning light comes on. The engine is subject to power loss and higher fuel consumption. The engine may also run irregularly. It can go into limp mode or even stall. Coolant can leak, creating green, pink or blue puddles under the vehicle. As a result, the coolant level drops and the corresponding light on the dashboard starts to illuminate. Leaking coolant has a strong sweet smell. A poorly functioning heater blows cold air into the cab while the engine is warm. The heater motor does not switch on or keeps running. A poorly functioning A/C system does not blow cold enough. We hear a clicking sound when switching on and the smell is musty. A poorly functioning intercooler system mainly causes performance and engine-behaviour symptoms.

The importance of timely and preventive maintenance of the cooling system

It prevents expensive engine damage due to overheating. There is less risk of breakdowns. It ensures a constant engine temperature, also in traffic jams, under heavy load and in hot weather. It extends the service life of the engine. It increases the vehicle’s reliability and therefore safety in traffic and on site. It prevents internal corrosion, limescale and sludge formation in cooling components. It guarantees the efficiency of the heat exchangers.

Repairing or replacing cooling components

Cooling parts are repaired or replaced depending on the type of defect, the reliability after repair, and the cost–benefit analysis. Repair makes sense if the component is still structurally sound and the repair is reliable and durable. Parts should be replaced when they are wear-sensitive, show internal defects, and when repair offers no guarantee of reliability.

Cooling systems tailored to heavy-duty applications

The heavier and longer the load, the more robust the cooling system must be. In a warm climate and under heavy work, a larger radiator is fitted to increase cooling capacity. The engine thermostat regulates the engine’s operating temperature by controlling the coolant flow. This thermostat ensures that the engine quickly reaches operating temperature and keeps the engine at a constant and optimal temperature. It prevents both overheating and running too cold. A thermostat is designed for a selected temperature, also called the opening temperature. When, due to engine operation, the coolant warms up to that selected temperature, the thermostat opens other cooling circuits. This starts the coolant flow to additional circuits, effectively increasing cooling. For heavily loaded trucks, a thermostat with a lower opening temperature is therefore fitted so that increased cooling is activated sooner.

Practical advice from experience when maintaining the cooling system

Coolant circuit and associated heating system

• Check the coolant present for quality. If the coolant no longer meets requirements, replace it with new coolant. To do so, drain the old coolant, then flush the circuit and fill it with new coolant. Bleed the circuit and ensure there is enough coolant in the circuit. Check all connecting hoses and lines, couplings and seals for tightness so that no coolant can leak from the system. Replace hoses, lines, couplings and seals where necessary.
• Check the expansion tank for cracks and deformation. Check the coolant radiator and the heater core for clogging. Replace them with new parts where necessary. Check the operation of the thermostat, the water pump, the fan and the viscous coupling. Check heat output at the interior heater. Check whether the heater flap opens and closes correctly according to the requested temperature in the cab.
• Intercooler circuit
• Check all connecting hoses and lines, couplings and seals for tightness so that no air can leak from the system. Replace hoses, lines, couplings and seals where necessary. Clean the outside with a mild degreaser where needed. Clean the inside of the circuit with air. Check that the intercooler is not clogged. Do this by measuring the air pressure loss. Check that the intercooler is not clogged crosswise. The intercooler receives air from the turbo. This turbo air contains fine oil vapour that is removed by the oil separator. Check the operation of this oil separator.
• A/C circuit
• Check all connecting hoses and lines, couplings and seals for tightness so that no refrigerant can leak from the system. Replace hoses, lines, couplings and seals where necessary. Check the pressure and level of the refrigerant. Check proper refrigerant circulation by measuring and observing. Check cross contamination of the condenser and the evaporator. Replace the cabin filter. Top up the refrigerant correctly. Check correct operation via the cold airflow in the cab. Check the operation of the A/C compressor.

The added value of Braem for cooling parts

Braem has an extensive stock of cooling parts for MAN and Mercedes trucks, buses and vans. Thanks to fast availability and technical expertise, repairs can be carried out efficiently.

Customers choose Braem because of:

• Good quality through thorough quality control
• Technical support during disassembly and installation
• Fast delivery within Europe and beyond
• Transparent warranty and return conditions

A reliable cooling system is indispensable for professional vehicle use. With the right parts and expertise, the engine remains protected against overheating and runs efficiently. The A/C system provides comfort for the driver.