Engine Compartment Hose Inspection

Under the effect of high temperatures inside the engine compartment, rubber and plastic hoses that serve various engine components and the exhaust emission control system gradually harden and deteriorate. The hoses should be checked periodically for cracks, hardening, loose connections and leaks.
The procedure for inspecting the cooling system hoses is described in subsection 2.6.6.
Some hoses are secured with clamps. Check the clamp tightness, since loose clamps lead to leaks. Where clamps are not provided, check the hose seal on the connection fittings. Loss of elasticity in such connections due to swelling or hardening of the hoses is not permitted, as this would cause the connection to leak.

Vacuum Hoses

PROCEDURE
1. Vacuum hoses can be identified by their color or by colored stripes applied to them. Different engine systems use vacuum hoses with different wall thicknesses, resistance to collapse from atmospheric pressure and heat resistance. When replacing, make sure that the new vacuum hoses exactly match the ones being replaced.
2. In many cases, a hose can only be checked after removal from the vehicle. If several hoses are removed, first make alignment marks on the mating fittings and hoses so that their relative positions are not disturbed later.
3. When inspecting vacuum hoses, also inspect the plastic tees. Check them for cracks, as well as for deformation of the hose where it fits onto the tee fitting, which may cause a leak.
4. To check for leaks by sound, a piece of vacuum hose with an inside diameter of approximately 6.0 mm (1/4 in.) can be used. Place one end of the hose at the suspected location and listen at the opposite end. A characteristic "hissing" sound indicates a leak.

Fuel Hoses

PROCEDURE
1. Check the condition of the rubber fuel hoses for signs of wear or deterioration. Pay particular attention to hoses at bends and near connections, for example at the connection to the fuel filter.
2. When replacing the fuel line on fuel-injected engines, the new line must exactly match the one used in the fuel system of engines of this type.
3. Spring clamps are usually used to secure fuel line hoses; they lose their elasticity over time. When disconnecting the connection, the clamp must be opened, after which its elasticity is permanently lost. When replacing hoses, always replace spring clamps with screw-type clamps.

Metal Tubes

INSPECTION PROCEDURE
1. Metal tubes are usually used in the fuel line to connect the fuel pump with the fuel pressure regulator on the fuel rail. Inspect the tubes for deformed (kinked) sections and small incipient cracks.
2. When replacing, install only seamless steel tubes. Copper or aluminum tubes are not suitable, as they cannot withstand vibration loads from the engine.
3. Inspect the metal brake lines and fittings at the connection to the master cylinder and proportioning valve (if equipped). Cracks and loose connections are not permitted. If any sign of brake fluid leakage is found, immediately inspect the entire brake hydraulic circuit thoroughly.