Note. See also Section materials Checking the condition and replacing the engine compartment hoses, localizing leaks.
Many serious engine malfunctions are related to malfunctions in the cooling system. If the car is equipped with an automatic transmission, then its operation and service life are also directly related to the operation of the cooling system.
Checking the cooling system should be carried out with a cold engine, so it is best to do it before the first trip of the day or no earlier than three hours after turning off the engine.
Slowly, being careful in case the engine is still warm, remove the expansion tank cap. Rinse thoroughly inside and out with clean water. Also clean the filler neck of the tank. The presence of traces of corrosion in the filler neck means that the coolant should be replaced. The coolant inside the expansion tank should be relatively clean and clear. If it has a brownish color, empty the system and fill it with new coolant.
Hoses, as well as drive belts, tend to fail at the most inopportune moment - in order to avoid troubles associated with rupture of radiator or heater hoses, carefully inspect them, as shown in the illustration.
1. Carefully check the radiator hoses, as well as the heater hoses, which have a smaller diameter. Check the entire length of the cooling system hoses, replacing any cracked, swollen or worn hose. Cracks are easier to find if the hose is squeezed by hand. Pay special attention to the clamps holding the hoses to the cooling system components. These clamps can cut or puncture hoses, causing coolant to leak.
2. Make sure all hose connections are secure. Coolant leaks usually show up as white or rusty deposits in the area of the seal failure. If your vehicle uses wire-type clamps, it makes sense to replace them with screw-type clamps.
3. Use compressed air or a soft brush to clean the front of the radiator (as well as the air conditioning condenser, where present). Remove all insects, leaves and other foreign objects that have fallen on the radiator fins - be very careful not to damage the fins or cut your fingers on them.
4. If the coolant level is constantly dropping, and you have not found any leaks, you should have the pressure test of the cooling system in a Mercedes-Benz workshop.
Checking the frost resistance of the coolant
Attention! Do not allow antifreeze to get on your skin and painted car surfaces! In case of contact, rinse immediately with plenty of water.
Antifreeze is extremely toxic and deadly if ingested.
Do not leave antifreeze in an open container or spilled on the floor; its sweet smell can easily attract children or pets.
Check local regulations for the disposal of used antifreeze. In many areas there are special centers for its acceptance.
1. Before the start of the winter season, it is imperative to check the concentration of antifreeze in the coolant, especially if clean water was poured into the system during operation - use a hydrometer with frost resistance graduation.
2. Slightly warm up the engine so that the top hose of a radiator warms up. When measuring the concentration of antifreeze, the temperature of the liquid should be about +20°C.
3. Carefully turn away a stopper of a broad tank.
Warning! When the engine is hot, open the expansion tank cap carefully. There is a risk of burns! It is necessary to put a rag on the cork. Open the plug only at a liquid temperature not exceeding + 90°C.
Draw liquid with a hydrometer bulb.
In our latitudes, the concentration of antifreeze is sufficient to protect the system to a temperature of -25°C, in a particularly cold climate up to -35°C.
Fluid removal
1. To remove coolant, place a drip tray under the radiator and remove the radiator drain plug.
2. It is impossible to completely remove the old fluid from the system (without complete engine disassembly), so all the volumes given in Specifications are conditional. In practice, you will be able to fill the system with about 2/3 of the prescribed amount of liquid.
3. After filling the system with fresh antifreeze, place a label on the expansion tank indicating the concentration, brand of antifreeze and date of replacement. Any subsequent replenishment of the system (before scheduled replacement) should only be carried out with the specified liquid.
Adding antifreeze
Note. Refer to materials Specifications at the beginning of the chapter.
If it is necessary to protect the engine down to -25°C, the concentration of antifreeze in the coolant should be 40%. If protection down to -35°C is required, the antifreeze concentration should be 50%.
Note. If a higher degree of frost protection is required, the antifreeze concentration level can be increased to 60%. This concentration will provide protection down to -40°C. If the concentration rises to a higher level, the protection of the engine starts to decrease and, in addition, the heat dissipation properties of the coolant deteriorate.
Air locks
If the engine overheats after changing the fluid, the cause is most likely due to air locks in the system. These plugs do not allow fluid to circulate throughout the system. They appear as a result of too hasty refueling of the system.
1. If you think there is an air lock in the system, first of all try to compress all available coolant hoses one by one. You can immediately tell if the hose is filled with liquid or air. As a rule, all air pockets disappear after the first (after fluid change) engine start.
2. With a warm engine running, turn on the heater and its fan. Warm air must be supplied to the passenger compartment in sufficient quantities. If the supply air temperature is low, an air lock may be the cause.
3. The consequences of air locks in the system can be very serious (not just a decrease in the efficiency of the heater). A large plug can stop the circulation of fluid inside the engine. In order to make sure that there are no plugs inside the engine, feel the upper radiator hose with the engine running - it should be hot. If the hose is cold, this indicates an air lock in the engine or a faulty thermostat.
4. If you could not get rid of air locks, let the engine cool down completely, remove the cap of the expansion tank, try to compress the system hoses. If this does not work, drain all the coolant into a clean container and refill the system with the same coolant following the instructions above.