Inspection and Replacement of Engine Compartment Hoses

(every 12,000 km [7500 miles] or every 6 months)

Replacement of A/C refrigerant hoses must be performed by qualified technicians at an automotive repair shop that has the necessary equipment to safely discharge the system. Never disconnect any refrigerant lines until the system has been completely discharged!

General Information
Under the high temperatures present in the engine compartment, the material of the rubber and plastic hoses routed there deteriorates over time. Regularly inspect all hoses under the hood for cracks, signs of leakage, hardening of the material, and loose connections at the fittings.

For detailed information on inspecting the condition of engine cooling and cabin heating system hoses, refer to the Cooling System Component Inspection section.

Some, but not all, hoses use clamps to secure them to their fittings. Check that hose clamps are tight; loose clamps lead to leaks. If a hose is installed on a fitting without a clamp, make sure its end remains flexible enough to seal tightly against the fitting surface.

Vacuum Hoses
Typically, all vacuum hoses, especially those used in emission control systems, are marked with a color code or have colored stripes fused into their walls. Different systems may require different wall thicknesses for their vacuum hoses. Hoses must provide different resistance to collapsing, temperature effects, and other factors. Make sure replacement hoses match the specifications of the original hoses.

It is usually only possible to reliably assess the condition of a vacuum hose after removing it from the vehicle. If more than one hose must be removed, label them clearly beforehand to ensure correct reconnection during installation.

When inspecting a vacuum hose, also check the condition of its plastic fittings. Inspect the fitting for cracks and make sure the hose fits tightly on it. When installed on the fitting, the hose must not deform unevenly, which would cause vacuum leaks.

A short section of vacuum hose with an inside diameter of about 7 mm makes an excellent stethoscope for locating vacuum leaks. Press one end of the hose against the surface being checked and place the other end to your ear. Vacuum leaks are always accompanied by a hissing sound. Warning: When listening to components, keep away from moving parts inside the engine compartment, such as drive belts, cooling fan blades, etc.!

Fuel Hoses

When servicing fuel system components, remember that gasoline is an extremely flammable liquid. Do not smoke near the work area and do not approach it with an open flame! Immediately collect all spilled fuel, and place fuel-soaked rags in a location where there is absolutely no possibility of accidental ignition! Always keep a Class B fire extinguisher within reach! Avoid getting gasoline on exposed skin - prolonged contact of this kind can cause the development of cancer. Remember that the fuel injection system is constantly under residual internal pressure, which must be released before beginning work (refer to the Fuel and Exhaust Systems section).

Inspect all rubber fuel hoses for signs of material aging and other defects. Pay particular attention to the condition of bends and the areas located directly in front of the ends fitted onto the connections.

Only high-quality fuel hoses must be used as replacement lines. Under no circumstances should non-reinforced vacuum hoses, clear plastic tubing or garden hoses be installed in the fuel system. Spring-type clamps are usually used to secure fuel hoses to connections. Such clamps lose their clamping force over time and, in addition, often unexpectedly slip off when the hose is disconnected. It is advisable to replace such clamps with more reliable and safer worm-drive or screw-type clamps.

Metal Lines
Sections of metal tubing are often used as fuel lines. Carefully inspect all rigid fuel lines for dents, kinks and other deformations. Make sure there are no cracks or signs of their beginning.

If any section of metal line requires replacement, use only seamless steel tubing as the replacement. Copper and aluminum tubing are not suitable as replacements, since they do not provide adequate resistance to the vibrations that occur in the system during engine operation.

Carefully inspect the metal brake lines at the points where they connect to the master cylinder and the proportioning valve (if equipped). Look for defects such as cracks, and check for signs of loosening of the fittings. If any signs of leakage are found, immediately inspect the entire brake system.