Mercedes-Benz ML350 Engine Overheating Diagnosis Cost

The engine cooling system is made up of a set of components connected in a closed loop to circulate engine coolant through the engine, and maintain the coolant at a constant temperature.

As the engine runs combustion events occur thousands of times per minute; heat is a byproduct of engine operation. To prevent that heat from destroying the engine, a liquid cooling system is used. Beginning with the engine, the cooling system uses coolant passages inside the engine block, cylinder head, and possibly the intake manifold. These passages allow coolant to flow through these components to absorb heat. The water pump pushes the coolant through the thermostat and into the radiator, where it is cooled, then returned to the engine for another cycle. The thermostat regulates the temperature as engine coolant will not move past the thermostat unless the set temperature has been reached. Since this is a pressurized system with no air, the engine coolant can reach extreme temperatures without boiling off as steam.

An overheating vehicle may have a temperature gauge that is reading higher than normal and into the red. The check engine light may illuminate, and the on-board diagnostic trouble codes stored for engine temperature and other issues. White or black smoke may be noted from the exhaust pipe under acceleration, and poor fuel mileage may be experienced. Contaminants may also be noted in the coolant reservoir, and coolant may actually flow out of it due to boiling over.

Driving a vehicle with a faulty engine cooling system can result in overheating, cylinder head gasket failure, engine block failure, or cylinder head warping. It is never recommended to drive a vehicle with engine cooling issues, especially with modern engine casting materials. Additionally, the operating conditions for the engine may cause fouling of the catalyst, and oxygen sensors.

All vehicles can experience cooling system issues in their useful service lives, without regard to age or mileage. Maintaining the cooling system according to manufacturer recommendations is the best thing an owner can do to prevent premature component failure. Engine coolant can become corrosive over time, and if the service interval for coolant servicing is not followed, the system will begin destroying itself from the inside out.

When diagnosing overheating issues, the servicing technician will connect a professional scan tool to the vehicle via the on-board diagnostics port under the dashboard. The technician will read the information stored in the vehicle's computer, and compare that data to actual conditions. A visual inspection of the cooling system, including the coolant level, condition of the reservoir, hoses, and the water pump belt will be performed. When suspected components have been narrowed down, the technician will make a recommendation for repair.

There are various problems and solutions for engine overheating. A stuck thermostat, non-functional cooling fan, a leaking headgasket, or multiple failures together could cause an overheating issue. Part replacement varies with the diagnosis. Water pumps can simply be replaced, but a blown headgasket is a much more involved repair. In addition to the head gasket itself, there are related seals and components that are recommended for replacement at the same time. There is also machining of the engine head that may be required to make sure the head surface is flat and level and able to seal with the new head gasket. Most repairs will require draining the engine coolant, and all will end with the re-filling of the coolant, bleeding the cooling system of all air, and final testing to ensure a completed repair.

Engine coolant flushes are often recommended needlessly, raising repair costs. However, there is a schedule for when these services should be performed. The factory scheduled maintenance section in the owner’s manual provides information for the customer concerning which maintenance items should be performed, and when they are needed. We always recommend following the factory scheduled maintenance intervals for preventive maintenance. If a leak is being repaired, the coolant may be drained and replaced. Flushing the coolant system should be performed if excessive corrosion is present, or if the factory scheduled service interval has passed.

It is a good practice turn the heater onto its highest setting if the engine begins to overheat. The heater core can act as a secondary radiator, but temperatures inside the vehicle may become unbearable.

The average DIYer can maintain the engine cooling system without much trouble. However, diagnosing the system when problems arise can be a daunting task if the function of each individual component is not fully understood. If knowledge of the engine cooling system and diagnosing cooling issues is lacking, this repair should be handed to a certified technician to prevent further damage and unnecessary expense.