Checking fluid levels, leak control (Mercedes-Benz S-Class W140)

Note. The following procedures are used to check the liquid level every 400 km or weekly. Other fluid level checks can be described later in the Sections on specific maintenance procedures. Regardless of the scheduled check intervals, do not allow liquid to leak under the vehicle - such leaks indicate a malfunction that should be corrected immediately.

Attention! When checking the level of any working fluid, the car must be positioned strictly horizontally!

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. Before adding fluid to any of these components, study the requirements Specifications to the types and volumes of liquids used.

Engine oil

Visual inspection of leaks

If the engine is oily and has a high oil consumption, check the most likely places for leaks:

• Filler cap sealing element - check for cracks and other mechanical damage;
• Components of the crankcase ventilation system (in particular - the ventilation hose running from the cylinder head cover to the air intake hose);
• Cylinder head cover gasket;
• Cylinder head gasket;
• Engine Oil Pan Drain Plug O-Ring;
• Oil filter gasket - carefully examine the place where the filter fits to the flange;
• Oil pan gasket.
• Front and rear crankshaft oil seals.

Wrap the generator in plastic, spray the engine with a regular cold cleaner, then, after a short time, rinse with water at a car wash.



Sprinkle the outside of the joints of the mating surfaces and the sealing elements of the power unit with lime or talc.

Check the oil level and top up if necessary.

During the short (about 30 km) trips (preferably on the expressway) warm up the engine - warmed up oil has increased fluidity and seeps through leaks more easily.

Park the car and, using a lamp, examine the engine to locate the sources of oil leaks.

Eliminate the causes of leaks.

Checking the level

Note: The maximum permissible engine oil consumption is 1l/1000 km, the actual level of oil consumption depends on the driving style - frequent driving with high engine speeds leads to increased oil consumption.

Note: Information on the operating principle of the engine oil level warning lamp is provided in Section Instrument cluster, gauges and control lamps and indicator lights Chapters User manual

A warning lamp built into the ignition switch assembly warns the driver of a dangerous drop in engine oil level (see section Instrument cluster, gauges and warning lamps and indicator lights Chapter Owner's Manual). The oil level switch sensor is located under the vehicle, in the right front corner of the engine oil pan.













The engine oil level is checked using a dipstick inserted into the guide tube and lowered into the engine to the bottom of the oil pan. The oil level should be checked before the first trip of the day, or about 5 minutes after the engine has been stopped. If the check is performed immediately after the engine has been turned off, the results will not adequately reflect the situation, since some of the oil will be distributed throughout the internal galleries and components of the engine.



Remove the dipstick from the guide tube and wipe the blade dry with a clean rag or paper towel. Insert the dipstick back into the tube until it stops, then remove it again. Inspect the dipstick blade and estimate the size of the area wetted with oil. The oil level should be between the upper and lower marks on the dipstick blade. If necessary, add the appropriate amount of oil of the required grade to the engine.

Lowering the level beyond the lower limit of the permissible range leads to the development of oil starvation of the engine, which is fraught with serious mechanical damage to the latter. Also try not to overfill the oil above the upper mark, as this can lead to spark plugs being thrown or failure of the power unit seals due to excessive pressure increase.



To fill the engine with oil, remove the threaded filler cap. To avoid oil splashing when filling the engine, use a funnel or a long-nosed oiler. After filling the engine with oil, screw on and tighten the filler cap securely, then start the engine and carefully inspect the drain plug and the surface of the oil filter mating with the block for signs of leaks.

Turn off the engine, wait 5-10 minutes for the oil to drain into the pan, then check its level again.

Note: Excess oil must be drained or pumped out - excessive engine oil level can cause failure of the catalytic converter. Make sure the filler cap is securely tightened.

Checking the engine oil level is an important preventative maintenance procedure for the engine. A constant decrease in the level indicates the presence of oil leaks due to failure of seals, damage to sealing gaskets, wear of piston rings or valve guides. If the oil is milky in color or consistency, or if there are drops of water in it, this indicates possible damage to the cylinder head gasket, or the formation of cracks in the body of the head(s) or block. The check must be done without delay. When measuring the oil level, always also check its condition. Use your thumb and forefinger to remove traces of oil from the dipstick blade - if there are small metal particles in it, the oil must be replaced (see section Changing engine oil and oil filter).

Engine coolant

Caution! Avoid contact of antifreeze with exposed areas of the body and painted surfaces of the vehicle.

Any accidental splashes should be washed off immediately with plenty of water.

Remember that antifreeze is a highly toxic liquid and its ingestion into the body, even in small quantities, can have the most serious consequences, including death.

Never leave antifreeze stored in a loosely closed container; immediately collect any coolant spilled on the floor.

Remember that the sweet smell of antifreeze can attract the attention of children and animals.

Consult with your local authorities about methods of disposal of used coolant - in many regions of the world there are special collection points for various types of waste.

Never pour old coolant down the drain or onto the ground!

Note: Non-toxic grades of antifreeze have been developed in recent years, but they must still be disposed of in an orderly manner.

All vehicles covered in this Manual are equipped with a compensating cooling system that operates under excess pressure. 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 reservoir. When the engine cools down, the coolant automatically flows back into the cooling system, which ensures that its level is maintained at a constant value. A warning lamp included in the instrument cluster warns the driver of a dangerous drop in the coolant level (see section Instrument cluster, gauges and control lamps and indicator lights Chapters User manual). The coolant level switch sensor is located at the bottom of the expansion tank of the cooling system.

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 should reach the "MIN" mark in the expansion tank. When the coolant is hot, the level should be approximately 1.5 cm higher. If necessary, make the appropriate adjustments - add a 40%/60% mixture of ethylene glycol antifreeze with water (see Specifications).

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 top up to the required level with the required mixture.

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.



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

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

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.

The brake master cylinder is installed in the rear left corner of the engine compartment. The driver is warned of a drop in the brake fluid level by a warning lamp built into the instrument cluster (see section Instrument cluster, gauges and control lamps and indicator lights in the Chapter User manual) the float switch of which is built into the cover of the master cylinder reservoir.

The brake fluid level is checked visually, using the marks on the plastic reservoir mounted on the master cylinder. The fluid level should be between the "MAX" and "MIN" 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.

While the reservoir cap is off, check the fluid and master cylinder reservoir for contaminants. If there are rust particles, dirt or water droplets, the system should be drained and new fluid added.

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

The fluid level in the master cylinder will drop slightly as the brake pads wear. There is no need to top up 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 (see section Checking the brake system).

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

If the fluid level check reveals that the reservoir is empty or nearly empty, the brake system should be checked for leaks and bled (refer to Chapters Clutch and Brake system).

Power steering system fluid (GUR)

Caution! If the fluid level in the reservoir has dropped below the fluid temperature zone, the power steering must be checked by a specialist workshop, as there is a loss of fluid. In this case, simply topping up the fluid level is not enough.

The power steering fluid level is checked at a temperature of about 20°C. The fluid level should be between the "MIN" and "MAX" marks on the plastic reservoir indicator(except for models equipped with 120 series engines)/blades of the measuring probe built into the tank lid (models with 120 series engines). The total volume of the tank is 1.4 l.

Note: Information on adjusting the power steering fluid level for diesel models was not provided by manufacturers at the time of writing this Manual, but the principle is similar to one described above for gasoline engines.

Windshield/Headlight Washer Fluid

Warning! Windscreen washer concentrate is highly flammable! When handling windscreen washer concentrate, the use of fire, open flame and smoking are prohibited.

The windshield washer fluid is contained in a plastic reservoir in the right front corner of the engine compartment. The filler neck of the reservoir is located in the front panel and is located between the right headlight and the radiator. The capacity of the reservoir is given in Specifications.

The driver is warned of a drop in the coolant level by a warning lamp built into the instrument cluster (see section Instrument cluster, gauges and warning lamps and indicator lights Chapter Owner's Manual). The control lamp switch sensor is mounted in the upper part of the coolant reservoir.

In temperate climates, the system can be filled with regular water, but it is recommended to add glass cleaner to the water (summer concentrate MV has the S marking). 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 concentrate should be used (w marking), which lowers 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.

Warning! Do not use antifreeze in the cooling system - it will damage the painted surfaces of the car!