Heater hose carries hot coolant from the engine to the cabin heater matrix and back. It is a smaller bore than radiator hose - typically 16mm to 25mm - and it is designed to be flexible enough to snake round a bulkhead and through tight spaces. The temperature and pressure duty is very similar to radiator hose; the difference is size and flexibility.

Internal diameters of 16mm, 19mm, 22mm and 25mm, cut to order from 1 metre up to a 20 metre full coil. Those four cover almost every automotive heater circuit as well as a great many agricultural and industrial hot water runs. Measure the outside diameter of the spigot on the heater matrix and the engine takeoff and match the hose bore to it.

A smooth black EPDM inner tube, reinforced with high-tensile fibre yarn, and a weather-resistant synthetic rubber outer cover. EPDM is the standard material for coolant service - it handles glycol antifreeze, hot water and the heat cycling of a cooling system, and the outer resists ozone and weathering so it does not craze and crack after a few years under the bonnet.

No. EPDM has poor resistance to hydrocarbons and will soften, swell and eventually fail. Heater hose is for coolant and hot water only. For fuel and oil use our SAE J30 R6 rubber fuel hose or a fluorosilicone-lined silicone hose - both are formulated specifically for that duty.

Age, heat cycling and coolant contamination. The classic symptoms are a sweet smell in the cabin, a damp passenger footwell, coolant loss with no visible external leak, and a hose that feels hard and brittle rather than pliable when you squeeze it. Because heater hoses are often tucked out of sight against the bulkhead, they tend to be forgotten until they let go.

Measure the run with a piece of string following the exact route, including the bends, then add a little for trimming. If you are replacing both feed and return, do them together - they are the same age and the second one will fail soon after the first. Buying a coil is more economical if you need more than a few metres.