Temperature increases inside the hood can cause rubber and plastic hoses of engine, accessory and emission systems degrade and thus require regular checks for cracks, loose clamps, hardening of the material and leaks. Most hoses are fitted with clamps and these should be tightened so as to avoid leakage; if there are no clamps, one should check whether the hose has swollen or become rigid at the junction. The PCV system releases crankcase blow-by gas through a rubber hose to the intake manifold where it is combined with the air intake before combustion and thus the PCV hose should be checked for cracks and blockage, it should then be cleaned using a solvent if blocked. vacuum hoses may be of different colours and should be replaced when the wall thickness become too thin and the temperature resistance is low; it is better to remove hoses for check or for some closing it is better label it for installation further. Check plastic T-fittings for cracks and hose distortions which can cause leak and use a small piece of vacuum hose as it is a stethoscope to find vacuum leaks. Fuel lines, most of which are made from flexible hoses, should be inspected as to its deterioration particularly at the bends and fittings; only the proper hose for the particular application of fuel injection system should the old hose be replaced with. Typically, spring-type clamps on fuel return or vapour lines should be replaced with screw clamps and special tools may be required for spring lock couplings. Fuel lines contain metal lines and must be checked for bend, crimps, or cracks; the preference for replacement is seamless steel tubes, as copper and aluminum cannot handle the pressure. Further, the metal brake line must be checked for cracks or loosing of the fittings and any sort of leakage of the brake fluid indicates the need to inspect the brake system.