Checking the condition and replacing the engine compartment hoses (BMW 5 Series E28)

Twice a year or every 10,000 km (whichever comes first).

Air conditioning hoses should be replaced at a dealer service station or a specialized workshop equipped to safely relieve system pressure. Never disconnect system hoses or remove system components without first relieving the pressure.

General information

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.

Information regarding cooling system hoses is provided in Section Checking the functioning of the cooling system, and to the brake system hoses - in Section Checking the brake system.

Most (but not all) hoses are secured with clamps. Where clamps are used, check that they are securely fastened to prevent leaks. If clamps are not used, check that the hose at the fitting has not swollen and/or hardened, allowing leaks.

Vacuum hoses

Typically, vacuum hoses, especially those used in emission control systems, are color-coded or have colored stripe inserts.

Different systems require hoses with different wall thicknesses, heat resistances, and collapse resistances. When replacing hoses, make sure the material of the new hose matches the material of the old one.

Often the only reliable way to check the condition of a hose is to remove it completely from the vehicle. If removing more than one hose, be sure to clearly label the hoses and fittings to ensure proper reassembly.



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

To detect vacuum leaks, you can use a small piece of vacuum hose as a stethoscope. Hold one end of the hose to your ear and listen with the other end to all vacuum hoses and connections for the characteristic hissing sound that indicates a vacuum 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 lampshades to the work site. Immediately collect spilled fuel with rags, which are then placed in a place where it cannot spontaneously ignite. If fuel gets on your skin, wash it off immediately with plenty of water and soap. When working with the fuel system, wear safety glasses and always have a fire extinguisher at hand.

Fuel lines are usually under pressure, so when disconnecting them, be prepared for fuel to spray out and need to be collected.

On vehicles equipped with fuel injection, the system pressure must be relieved before servicing the fuel hoses. For instructions, refer to Chapter Power supply system.

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.



Use only high quality fuel hoses. Never, under any circumstances, use non-reinforced vacuum hoses, clear plastic tubing or water hoses as fuel hoses.

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

Metallic lines

There are often sections of metal tubing between the fuel pump and the fuel injection system. Check these tubing carefully for dents, twists, or cracks.

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

Check the metal brake lines where they connect to the master cylinder and to the pressure equalization unit or ABS (if it exists) for cracks or loose fittings. Any signs of brake fluid leakage require immediate and thorough inspection of the entire brake system.

Power steering hoses

Check the power steering hoses for signs of fluid leaks, loose fittings, and worn clamps. Leaking hoses and worn clamps should be replaced.

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