Checking the condition and replacing hoses and tubes in the engine compartment, localizing leaks (BMW 7 Series E38)

Air conditioning (A/C) hoses should be replaced at a service station or workshop equipped to safely relieve the pressure in the A/C system. Never disconnect A/C hoses or remove components without first relieving the pressure.

General information

1. Exposure to high temperatures in the engine compartment will gradually deteriorate the rubber and plastic hoses used in various systems. Hoses should be checked regularly for cracks, loose clamps, hardening of materials, and signs of leaks.

2. Information regarding the cooling system hoses is provided in Section Checking fluid levels, leak control, and to the brake system hoses - in Section Checking the brake system and clutch.

3. Most (but not all) hoses are secured with clamps. Where clamps are used, check that they are tight enough to prevent leaks. If clamps are not used, check that the hose is not swollen and/or hardened where it connects to the fitting.

4. If there are signs of a fluid leak, but the type or origin of the fluid cannot be identified, leave the car for a long time and place a large piece of paper or rag underneath it. This will help you find the leak and identify the fluid by color. But keep in mind that some leaks may only appear when the engine is running.

Vacuum hoses

1. Usually, vacuum hoses, especially those used in the exhaust gas reduction (EGR) system, are color-coded or have inserts of colored stripes. Different systems require the use of hoses with different wall thicknesses, heat resistance and different collapse resistance. When replacing hoses, make sure that the material of the new hose matches the material of the old one.



2. Often the only reliable way to check the condition of a hose is to remove it completely from the vehicle. When removing several hoses at a time, mark their ends and fittings to ensure proper reassembly.

3. When checking the vacuum hoses, be sure to also check the plastic T-joints. Inspect them for cracks that could cause leaks.

4. A leak in the vacuum hose means that air is being sucked into the hose (but it doesn't come out of the hose), and this makes the leak difficult to detect. To detect vacuum leaks, you can use a small piece of vacuum hose as a stethoscope. When the end of the hose is directly over the leak, a hissing sound will be clearly audible through it. Listen to all vacuum hoses and connections for the characteristic hissing sound that indicates a leak.

When using such a stethoscope, be careful not to allow contact with moving components in the engine compartment, such as the drive belt, cooling fan, etc.

Fuel hoses

When inspecting or servicing fuel system components, certain precautions must be taken. Perform all work in a well-ventilated area and keep away from open flames (for example, lit cigarettes) or unprotected lamp shades to the work site. Immediately collect spilled fuel with rags, which are then placed in a place where it cannot ignite. If fuel gets on your skin, wash it off immediately with plenty of water and soap. When working on the fuel system, wear safety glasses and always have a fire extinguisher at hand.

1. Fuel hoses are usually under pressure, so be prepared to collect any squirting fuel when disconnecting them.

On vehicles equipped with a fuel injection system, the system pressure must be relieved before servicing the fuel hoses (see section Fuel system of gasoline engines Chapters Fuel and exhaust systems).

2. Check all rubber fuel hoses for signs of wear and tear. Pay particular attention to bends and in front of fittings, such as where the hose connects to the fuel pump or filter, where cracks may form.

3. Use only high quality fuel hoses. Never use non-reinforced vacuum hoses, clear plastic tubes or water hoses as fuel hoses.

4. Band-type clamps are commonly used to secure fuel hoses. These clamps will weaken over time and may "pop out" when removed. When replacing hoses, replace these clamps with screw-type clamps.

5. Minor fuel leaks are difficult to pinpoint because fuel tends to evaporate quickly once it comes into contact with air, especially in a hot engine compartment. Small droplets may disappear before the leak can be located. Metal fittings contract as they cool, and rubber hoses will be loosened, so potential leaks will be more obvious as the engine warms up when starting from cold.

Metallic lines

1. There are sections of metal tubing installed between the fuel pump and the fuel injection system and these should be carefully checked for dents, twists or cracks.

2. If a section of metal line needs to be replaced, use only seamless steel tubes, as copper and aluminum tubes are not strong enough to withstand vibrations caused by engine operation.

3. Check metal brake lines where they connect to the master cylinder, pressure regulator/ABS actuator for cracks or loose nipple connections. Any signs of brake fluid leakage require immediate and thorough inspection of the entire brake system.

(The article text was copied from an online resource: «BMWMAN.RU»)