3.12. Check of functioning of the cooling system and frost resistance of cooling liquid, liquid replacement

Address also materials of the Section Check of a State and Replacement of Hoses of a Motive Compartment, localization of leaks.

Hoses, also as well as driving belts, have property to fail at the most inappropriate moment - in order to avoid the troubles connected with a rupture of hoses of a radiator or a heater attentively examine them, as shown in an illustration


  1. Many serious violations in operation of the engine are connected with malfunctions of the cooling system. If the car is equipped with automatic transmission, then its functioning and service life are also directly connected with operation of the cooling system.
  2. Check of the cooling system has to be made at the cold engine therefore it is better to be engaged in it before a trip, the first for the present day, or not earlier than in three hours after switching off of the engine.
  3. Slowly, being careful in case the engine yet not absolutely cooled down, uncover a broad tank. Carefully wash out it clear water from within and outside. Also wash out a jellied mouth of a tank. Existence of traces of corrosion in a jellied mouth means that cooling liquid should be replaced (see below). Cooling liquid in a broad tank has to be rather pure and transparent. If it has brownish color, empty system and fill in in it new cooling liquid.
  4. Carefully check radiator hoses, and also heater hoses which have smaller diameter. Check cooling system hoses on all length, at identification of cracks, swellings and signs of aging of material you make replacement. It is easier to find cracks by tightening of a hose. Pay special attention to installation sites of fixing collars which can cut or pierce hoses that will lead to development of leak of cooling liquid.
  5. Make sure of reliability of fastening of all hose connections. Leak of cooling liquid is usually shown in the form of white or rusty color of deposits in the field of sealing violation. If on your car collars of wire type are used, then it makes sense to replace them with collars of screw type.
  6. By means of compressed air or a soft brush clear a forward part of a radiator (and also the air conditioner condenser where it is available). Remove all insects, the leaves and other foreign objects which got on radiator edges, - be very careful not to injure an edge and not to cut about them fingers.
  7. If the level of cooling liquid constantly falls, and you did not find any leaks, it is necessary to make check of the cooling system pressure in conditions HUNDRED Mercedes-Benzs.

Check of frost resistance of cooling liquid

Do not allow hit of antifreeze on your skin and the painted surfaces of the car. At hit immediately wash away a plentiful amount of water. Antifreeze is extremely toxic and deadly at hit in an organism. Do not leave antifreeze in an open container or spilled on a floor; its sweetish smell can easily attract to itself children or pets. Consult about local rules of utilization of the fulfilled antifreeze. In many areas there are special centers for its acceptance.


  1. Before a winter season it is necessary to check surely concentration of antifreeze in cooling liquid, especially if in system clear water was in use filled in, - use the areometer with graduation on frost resistance.
  2. Slightly warm up the engine so that the top hose of a radiator heated up. At measurement of concentration of antifreeze temperature of liquid has to make about +20 °C.
  3. Carefully turn off a stopper of a broad tank.

At the hot engine the stopper of a broad tank should be opened carefully. There is a danger of a burn! It is necessary to put a rag on a stopper. Open a stopper only at a temperature of liquid no more than + 90 °C.

  1. Gather liquid by means of an areometer pear.
  2. In our latitudes the concentration of antifreeze providing protection of system up to the temperature of -25 °C at especially frigid climate to -35 °C is sufficient.

Replacement of cooling liquid


  1. Prepare the drain capacity of suitable volume.
  1. Uncover a broad tank.
  1. Open an adjusting faucet of a heater.
  2. Remove protection of a case.
  1. Serially merge cooling liquid at first from a radiator (see сопр. illustrations and and b), then from an engine case (see сопр. illustration c).

    and — Location of the drain gate of a radiator, - pull a hose with an internal diameter of 12 mm (petrol models) on the gate
    b — Location of the drain gate of a radiator, - pull a hose with an internal diameter of 12 mm (diesel models) on the gate
    with — Location of a drain stopper of a water shirt of a case of the engine, - in case of need use a hose with an internal diameter of 14 mm




  1. Check passability of open sites of canals of a cooling path, in case of need make their clearing.

  2. Estimate a condition of sealing washers of drain traffic jams, replace defective washers.
  3. Through a mouth of a broad tank fill in the required amount of fresh cooling liquid in system. At operation of the car in conditions with a temperature up to -25 °C concentration of antifreeze in cooling liquid has to make about 40%. When lowering stem of thermometer to a mark of -35 °C it is necessary to increase concentration to 50% (see Specifications).

If higher degree of protection against freezing is required, it is possible to increase the level of concentration of antifreeze to 60% (such concentration will provide protection against freezing at temperatures up to -40 °C). Further increase in content in cooling liquid of antifreeze leads to decrease in efficiency of its action both at heat removal, and at protection of the engine against corrosion.

  1. Start the engine and release from a cooling path air traffic jams (see below).
  2. Fix on a cover of a broad tank a label with the indication of concentration, brand of antifreeze and date of its replacement. Any subsequent replenishment of system (before planned replacement) has to be made only by liquid of the same structure, or the distilled water

Removal of air traffic jams


  1. If after liquid replacement the engine overheats, the reason, most likely, available air traffic jams in system. Traffic jams usually appear as a result of haste when filling system do not break serviceability of circulation of cooling liquid.
  2. Presence at rubber hoses of the cooling system of air traffic jams usually rather just comes to light to the touch. After performance of replacement of cooling liquid air traffic jams usually disappear at the first start of the engine.
  3. At the working engine which is warmed up up to the normal working temperature include a heater and its fan, - warm air has to come to salon in enough. Presence in the highway of the cooling system of air traffic jams can be one of the reasons of insufficient warming up of air.
  4. Emergence in a cooling path of air traffic jams is fraught with time the most serious consequences, but not just leads to decrease in efficiency of return of a heater. Rather volume stopper can prevent circulation of liquid in a water shirt of the engine. To make sure of lack of traffic jams in the engine, feel the top hose of a radiator: at the working engine it has to be hot. Insufficient warming up of a hose can demonstrate presence at a shirt of air traffic jams, and also about possible malfunction of the thermostat.

Petrol models


  1. If after the first start of the engine after implementation of the procedure of replacement of cooling liquid in system there are air traffic jams, kill the engine and wait for its full cooling, then uncover a broad tank and a poszhimayta hoses of cooling. At worst the cooling system should be emptied and filled completely with fresh cooling liquid (see above).

Diesel models

G270 CDI (M612)

Preparation for removal of air traffic jams from a path of the cooling system of the turbocharged engine (1 of 4)

Preparation for removal of air traffic jams from a path of the cooling system of the turbocharged engine (2 of 4)

Preparation for removal of air traffic jams from a path of the cooling system of the turbocharged engine (3 of 4)

Preparation for removal of air traffic jams from a path of the cooling system of the turbocharged engine (4 of 4)

N90 — the Module of management of a cooler of air of pressurization


  1. Switch the AT selector lever to situation "P" and switch off ignition.
  2. Turn out fixing bolts (1), delay a cover (2) under the dashboard on the right down, turn out bolts (3) and uncover (4).

On the models equipped with system of an emergency call of TELE AID (ET2 code) disconnect an electrical wiring from the corresponding loudspeaker of the right forward door.

  1. Open the right forward door and release from clamps a side cover (5) on the right on the dashboard for the purpose of simplification of access to the module of management of a cooler of air of pressurization (N90).
  1. Remove the N90 module and you peremknit among themselves plugs No. No. 2 and 5 of a contact block for the purpose of short circuit of a contour of power supply of the circulation pulser (M44).

Be attentive: numbering of plugs on a block and on the socket of the module does not coincide!

  1. Open a cover of a broad tank and include ignition, - activation of the circulation pulser will lead to removal of traffic jams from a path of the cooling system.
  2. Having made sure of completeness of removal of air, switch off ignition and install into place the being removed components.

G400 CDI (M628)

During the procedure constantly watch liquid level in a broad tank, in case of need make the corresponding adjustment! When temperature of cooling liquid reaches value of 60-70 °C a cover of a broad tank it is necessary to close.


  1. On the models equipped with the series 628 engine removal of air from a cooling path it is made also by activation of an electric motor of the circulation pulser (M44).
  2. Connect and activate the reader STAR DIAGNOSIS (act according to the instructions provided in the instruction of manufacturers of the device).
  3. Make the choice of model of the car with the instruction like the engine and the steering drive.
  4. Enter into the main group of modules of management and choose the required driver.
  5. Specify type of a power supply system (CDI-V1).
  6. Choose the activation mode, having specified an electric motor of the circulation pulser (M44) as a target point.
  7. For activation of the pump press a function key of "F3", - the pump will function only at the pressed key.

The key has to be pressed physically, but is not virtual by means of a mouse!

Removal of oil from cooling and heating paths of diesel engines

Do not open a cover of a broad tank until cooling liquid does not get warm up to the temperature of 90 °C. When opening a cover be careful, - be not scalded!

Removal of oil from a cooling/heating path of the diesel engine

1 — the Broad tank
2a — the Drain gate of a radiator
2b — the Drain stopper of a case of the engine
3 — the Overflow tank (on the considered models it is not used)

1 — 8 Radiator
20 — the Thermostat
And — the Giving and returnable streams of a heater


  1. Remove protection of a case. Empty the cooling system (see above).
  2. Remove the cooling system thermostat (see the Head of the Cooling system, heating, ventilation and air conditioning).
  1. By means of flat-nose pliers remove a lock plate (6), then having pulled down and at the same time turning, take from a casing (4) thermostats a working element (5). Further the casing can be used as the device for removal from the oil cooling system.
  1. Include a heater on the maximum productivity (see the Part of the Device of ensuring comfort), at the corresponding complete set activate also additional heater (see in the same place).
  2. Fill in the special washing-out solution (5% of a concentrate for 95% of water) in the cooling system.
  3. Start the engine and on moderate turns warm up it up to the temperature about 80 °C (about 5 minutes will be required).
  4. Kill the engine and let's it cool down up to the temperature about 50 °C.
  5. Merge solution from the cooling system (see above).
  6. Fill the cooling system with clear water, for 5 minutes start the engine, then again muffle and merge water.
  7. Fill in fresh cooling liquid in the cooling system, remove from a cooling path air (see above) and examine system components on existence of signs of development of leaks.