Cooling water hose and line

Coolant hoses and pipes connect the radiator to the engine, coolant pump and expansion tank. They must accommodate pressure pulses, thermal expansion and relative movement between the engine and chassis without leaking or restricting the flow area. A perished radiator hose, corroded coolant pipe or leaking quick connector does more than cause fluid loss: trapped air and reduced circulation can also lead to localised overheating.

Always identify parts using the vehicle's chassis number. Visual comparison or selection based solely on the model name is never sufficient. On MAN TGS and TGX with D20 or D26 engines and Mercedes Actros with OM 471 engines, pipe routing, connections and branches may differ depending on the year of manufacture, emissions specification and cooling package. The vehicle-specific configuration is also decisive for buses such as MAN Lion's City and Mercedes Citaro, and vans such as MAN TGE and Mercedes Sprinter.

The range includes moulded supply and return hoses, bleed hoses, expansion tank connections and rigid coolant pipes. Hoses are generally made from textile-reinforced EPDM (ethylene propylene diene monomer); silicone versions are only suitable when the material, reinforcement and connections have been approved for the application. Rigid pipe sections may be made from steel, aluminium or engineering plastics.

Check the internal diameter, wall thickness, bend radius, connection profile and mounting bracket positions. For quick connectors, the insertion depth, locking mechanism and seal geometry must match. Working pressure, maximum permissible temperature and dimensional tolerances are determined by the vehicle specification; burst pressure is not a permissible operating pressure. A universal hose with the same diameter does not automatically provide sufficient kink resistance or the correct fit.

Typical faults include hardening, cracks near hose clamps, blistering and softening caused by contact with engine oil. Internal delamination of the reinforced hose wall can restrict flow even when the exterior appears intact. On metal pipes, corrosion and wear-through occur mainly beneath mounting brackets. Coolant deposits around connections often indicate minor leaks that evaporate under hot operating conditions.

1. Inspect when cold and depressurised. Never open a hot cooling system. Check the entire route for chafing marks, kinks, missing supports and damaged hose spigots. Once the system has cooled, feel accessible hoses for localised swelling or unusual softness.
2. Carry out a pressure test. Use a cooling system tester with a suitable adapter and pressure gauge. Pressurise the circuit only to the specified test pressure and record any pressure drop over the specified test period. Check connections and test the pressure cap separately in accordance with the manufacturer's procedure.
3. Investigate circulation problems. With the thermostat open, compare the temperatures at the radiator inlet and outlet using contact temperature sensors. Assess these readings alongside engine load, fan operation and diagnostic data; a temperature difference alone does not prove a blockage.
4. Identify the underlying cause. If hoses collapse, check the pressure cap's vacuum relief function and look for possible restrictions. If pressure builds up rapidly from a cold start, also investigate possible combustion gas ingress before replacing only the hose.

Drain the coolant in a controlled manner and clean the mating surfaces without abrading away material. Replace damaged spigots, sealing rings specified for replacement and non-reusable clamps. Fit hoses without tension or twisting, leaving sufficient clearance from exhaust parts and moving components. Position hose clamps in the specified clamping area and observe the specified tightening torque; overtightening can damage plastic connections.

Fill with coolant that meets the required manufacturer approval, rather than selecting by colour alone. Bleed the system according to the vehicle procedure and use vacuum filling equipment where specified. After warm-up and complete cool-down, recheck for leaks and check the mountings and coolant level. Braem can provide technical support with parts identification, ensuring that the correct connectors and mounting hardware are also included.