Radiator hose is the larger bore, carrying coolant between the engine and radiator; heater hose is smaller bore, typically 16mm to 25mm, running to the cabin heater matrix. Both are EPDM rubber built to SAE J20 R3 with a similar temperature and pressure duty - the difference is size and how flexible they need to be for the route they take.

Our straight radiator hose covers 5mm to 102mm internal diameter, cut from 1 metre to a 20 metre coil. Heater hose is 16mm, 19mm, 22mm and 25mm. Moulded 45 and 90 degree rubber elbows run 10mm to 76mm. Coupling joiners come in 25 bores from 5mm to 102mm in short and long lengths. Order by internal diameter to match the outside diameter of the pipe stub.

EPDM rubber to SAE J20 R3, rated -30C to +120C and glycol rated for standard antifreeze mixes. That is the specification of virtually all original-equipment coolant hose and it covers automotive, marine, agricultural and industrial cooling systems. It is not suitable for fuel or oil - hydrocarbons attack EPDM.

Whenever the hose has to resist vacuum or crushing - typically a long lower radiator hose that can collapse as the water pump pulls against it, any run on the suction side of a pump, or a hose that must bend tightly without kinking. Our wire reinforced radiator hose has a steel helix in the wall for exactly that, in 13mm to 51mm bores.

Use a moulded elbow for any real change of direction. Bending straight hose round a corner closes up the bore, restricts flow and creates a stress point that will eventually split. Our rubber 45 and 90 degree elbows are moulded with 150mm legs each side, 300mm in total, so there is plenty of material to trim to fit.

Age, heat cycling and coolant chemistry. The classic signs are a hose that feels hard and brittle or, conversely, spongy and swollen when squeezed; surface cracking when flexed; and seepage or crusty residue around the clips. Failure is often sudden and always inconvenient, so replace on condition rather than waiting - and always replace both hoses and the clips together.