Checking fluid levels, leak monitoring (Mercedes-Benz C-Class W203)

Contents: Engine oil ↡ 9. Diesel engine 612: the oil level…↡ Engine cooler ↡ Brake fluid ↡ Checking the oil level in the power…↡ Windshield washer fluid ↡

Note: The following procedures are for checking fluid levels every 1000 km (620 mi), monthly, and before each long trip. Other fluid level checks can be found in the Specific Maintenance Procedures Sections below. Regardless of the scheduled check intervals, do not allow fluid to leak under the vehicle; such leaks indicate a problem that should be addressed immediately.

Fluids are an integral part of the lubrication, cooling, braking and windshield washer systems. Due to the gradual consumption and/or contamination of fluids during normal vehicle operation, they should be replaced periodically. See the "Types and Volumes of Lubricants and Fluids Used" section in Specifications, before adding liquid to any of the listed components.

Note: Whenever checking the fluid level, the vehicle must be on a level surface.

Visually inspect the following pipes, hoses and connections for leaks, abrasions, cracks and damage:

Fuel lines;
Cooling system hoses;
Brake lines and hoses;
Power steering hydraulic lines;
Air conditioning lines.

Engine oil

Visual inspection of leaks

1. If the engine is oily and there is a high oil consumption, check for leaks. To do this, check the following places:

Check the filler cap gasket for cracks or damage.
Crankcase ventilation: ventilation hose from cylinder head cover to air intake hose.
Cylinder head cover gasket.
Cylinder head gasket.
Oil drain plug (round ring).
Oil filter gasket: filter fits to flange.
Oil pan gasket.
Front and rear crankshaft oil seals.

2. Since in the presence of a leak the oil spreads over a large surface of the engine, it is difficult to immediately determine the location of the leak.

3. Wash the engine. Cover the generator with a plastic bag. Spray the engine with a regular cold cleaner and after a short time wash it with water at a car wash.

4. Sprinkle the outside of the mating areas and seals on the engine with lime or talc.

5. Check the oil level and top up if necessary.

6. Take a test drive. Since oil in a hot engine reduces its viscosity and appears faster in leak areas, it is necessary to take a test drive of about 30 km on a high-speed highway.

Finally, examine the engine with a lamp and locate the leaks, eliminating the faults.

Checking the oil level with a dipstick

The oil level is indicated by an indicator located on the instrument panel (see above). In 4-cylinder petrol engines "271" from 6/02 production, as well as in 6-cylinder petrol engines and in diesel engines, the hole for the oil level indicator (1) is closed with a plug (2). In these engines, a special dipstick ET No.120 589 07 21 00 is used to check the oil level during maintenance.

4-cylinder petrol engine

1. Drive the car to warm up the engine and stop on a level surface.

2. After stopping the engine, wait about 5 minutes for the oil to drain into the oil pan.

If you start measuring the engine oil level immediately after turning off the engine, some oil will remain in the upper part of the engine, which will significantly affect the accuracy of the measurement.

3. Remove the oil level indicator (1) and wipe it with a clean cloth. (2) – oil filler hole cover.

4. Insert the level indicator into the hole until it stops and remove it again.

5. Check the oil level using the indicator. It should be between the MAX (3) and MIN (4) marks.

Caution: If the oil level is above the MAX mark, there is a risk of damage to the catalytic converter.

6. If the oil level is at or below mark (4), add oil up to the MAX mark. The difference in oil levels between the MAX and MIN marks corresponds to a volume of 2 liters.

Attention! If oil has been accidentally overfilled, it must be sucked out using a special device.

7. Oil is added through the plug (2) of the cylinder head cover. (1) – oil level indicator (refer to illustration 5.10). When topping up, use only the oil specified in the Specifications.

Attention! It is not recommended to combine oils of different types at random. If possible, do not mix oils of the same type but different brands. Engine oils of the same type, the same brand, but different viscosity, can be mixed if necessary.

6-cylinder petrol engine 112, diesel engines

1. Drive the car to warm up the engine and stop the car on a level surface.

2. After stopping the engine, wait about 5 minutes for the oil to drain into the oil pan.

3. Remove the cover (1) from the oil level indicator hole (2). (3) – fuel filter, the illustration shows a 611 diesel engine.

4. Insert the special oil level dipstick into the hole until it stops.

5. After 3 seconds, remove the dipstick and check the oil level using it.

Engine 112:

Oil level according to the dipstick	Oil volume
120 mm	4.00 l
126 mm	4.50 l
132 mm	5.00 l
140 mm	5.50 l
148 mm	6.00 l
154 mm	6.46 l
161 mm	7.00 l
168 mm	7.50 l
175 mm	8.00 l
183 mm	8.50 l
187 mm	8.75 l

6. Petrol engine 112: Recalculate the oil level given in the table to the corresponding volume. Determine the difference and add it to the engine if necessary.

7. Diesel engines 611:

Engines up to No.448 572 (Ind. No.30, Untertürkheim plant) and No.069 844 (Ind. No.40, Berlin plant)

MAX = 138 mm,
MIN = 110 mm.

Engines starting with No.448 573 (Ind. No.30, Untertürkheim plant) and engine No.069 845 (Ind. No.40, Berlin plant)

MAX = 127.5 mm,
MIN = 99.5 mm.

Note: The part number is located behind the 6-digit engine model designation, e.g. "611.962".

8. Diesel engine 612:

Engines up to No.134 163

MAX = 135 mm,
MIN = 110 mm.

Engines starting from No.134 164

MAX = 124.5 mm,
MIN = 99.5 mm.

9. Diesel engine 612: the oil level should be between the MAX and MIN marks.

Engine oil consumption

Max. 1l/1000km, depending on driving style.

The engine oil consumption can only be determined after driving a long distance. During the running-in period, it may exceed the specified value. Frequent driving with high engine speeds leads to increased oil consumption.

Checking the oil level is an important preventive procedure. A constant drop in the oil level indicates either leaks through damaged seals or loose connections, or oil is being burned out (internal leaks through worn piston rings or through valve guides). In addition, you should pay attention to the condition of the oil itself. If the oil is milky in color or drops of water can be seen in its composition, this indicates a possible leak in the cylinder head gasket or a crack in the head or cylinder block. In this case, the engine should be repaired immediately. Each time you measure the oil level, before wiping the dipstick blade, run your thumb and forefinger over it. If you find dirt or metal particles stuck to the dipstick, the oil should be replaced (refer to Section Changing engine oil and oil filter).

Engine cooler

Warning! Do not allow antifreeze to come into contact with your skin or the painted surfaces of your vehicle. If this does happen, wash off the antifreeze immediately with plenty of water. Antifreeze is extremely toxic if ingested. Never leave it unattended in an open container or spilled on the floor; children or animals may be attracted to its sweet smell and may drink it.

(Material taken from a web resource: Mercedesman.ru)

1. All vehicles covered by this manual are equipped with a compensating positive pressure cooling system. The white plastic expansion tank is located in the engine compartment and is connected to the radiator by a hose. As the engine warms up during operation, the expanding coolant fills the tank. As the engine cools, the coolant automatically flows back into the cooling system, which maintains a constant level.

2. The coolant level in the reservoir should be checked regularly, with the vehicle in a strictly horizontal position and the engine turned off. When the coolant is cold, its level in the expansion tank should reach the level indicated by the arrow in the illustration.

When the coolant is hot, the level should be approximately 1.0 cm higher.

Add 40%/60% ethylene glycol antifreeze mixed with water. The composition specified in the Specifications should be used.

Caution! Do not remove the expansion tank filler cap or the radiator cap to check the coolant level until the engine has cooled down completely! The level in the reservoir fluctuates depending on the engine temperature. When the engine is cold, the coolant level should be above the "MIN" mark on the reservoir. As the engine warms up, the level should approach the "MAX" mark. If this is not the case, allow the engine to cool down and then remove the cap from the reservoir.

3. Run the vehicle and measure the coolant level again. If only a small amount of coolant needs to be added to the required level, you can use clean water to do this. However, frequent additions of water will dilute the antifreeze. To ensure the correct ratio of antifreeze to water, always add the required mixture to the required level.

4. If the coolant level drops regularly, there may be a leak in the system. Inspect the radiator, hoses, filler cap, drain plugs and water pump (refer to Section Checking the functioning of the cooling system and frost resistance of the coolant. Replacing the liquid). If no leaks are found, check the tightness of the expansion tank cap and radiator at a service station.

5. If you need to remove the cover, wait until the engine has cooled down completely, then wrap a thick rag around the cover and unscrew it to the first stop. If steam or coolant starts escaping from under the cover, allow the engine to cool down a little more before removing the cover.

6. It is also necessary to check the condition of the cooler. It should be relatively clean. If the liquid is brown or rusty, it must be drained, the system flushed and filled with a new mixture. Even if the cooler looks normal, the corrosion inhibitors in its composition lose their effectiveness over time, so it should be replaced at certain intervals.

7. To check the frost resistance of the coolant, it is necessary to use a hydrometer.

Brake fluid

Warning! Brake fluid can cause eye damage and damage painted surfaces, so be extremely careful when handling it. Do not use brake fluid that has been open for a long time or that is more than one year old. Brake fluid tends to absorb moisture from the air, which can lead to a dangerous loss of braking efficiency. Use only the recommended type of brake fluid. Mixing different types of fluid can cause brake failure.

1. The brake fluid reservoir (1) is located at the rear left in the engine compartment. It has two chambers, each for its own brake circuit.

2. The brake fluid level is checked visually, using the marks on the plastic reservoir mounted on the master cylinder. With the cap closed, the brake fluid level should be between the MAX (2) and MIN (3) marks. If the level is below the acceptable level, first wipe the top of the reservoir and the cap with a clean rag to prevent dirt from getting into the system after removing the cap. Top up to the required level with the recommended fluid, but do not overfill.

3. While the reservoir cap is removed, inspect the fluid and master cylinder reservoir for contamination.

If it contains particles of rust, dirt or water droplets, the fluid from the system should be drained and new fluid should be added.

4. After filling the reservoir to the required level, make sure the lid is installed level to avoid liquid leakage and/or dirt ingress.

5. The fluid level in the master cylinder will drop slightly as the brake pads wear. There is no need to add more fluid as long as the level remains near the "MIN" mark; it will rise after replacing the linings. A very low level may indicate worn brake pads. Check them for wear (refer to Section Checking the brake system. Adjusting the parking brake).

6. If the brake fluid level drops continuously, immediately check the entire system for leaks. Inspect the brake lines, hoses and fittings, together with the calipers, wheel cylinders and master cylinder (refer to Sections Checking the brake system. Adjusting the parking brake, Checking the condition and replacing engine compartment hoses, localizing leaks).

7. If the reservoir is empty or nearly empty when checking the fluid level, the brake system should be checked for leaks and bled (refer to Chapter Clutch and drive shafts).

Checking the oil level in the power steering hydraulic system reservoir

The power steering hydraulic reservoir is located at the rear of the engine compartment. Refer to Section Checking the power steering fluid level.

Windshield washer fluid

Glass cleaner concentrate is highly flammable.

When handling glass cleaning concentrate, the use of fire, open flame and smoking are prohibited.

1. Open the cover (1) and visually check the liquid level.

2. If necessary, top up with a mixture of glass cleaner concentrate and drinking water. The capacity of the tank is given in the Specifications.

3. In temperate climates, the system can be filled with regular water, but it is recommended to add glass cleaner to the water. The reservoir should be no more than two-thirds full to allow for expansion of the water when it freezes. In cold climates, a special windshield washer antifreeze should be used to lower the freezing point of the liquid, which can be purchased at any car accessory store. It is usually sold in concentrated or ready-made form. If you purchased concentrated antifreeze, mix it with water according to the manufacturer's instructions on the package.