Heater Hoses

Heater hoses are the engine bay’s small-bore coolant lines: the heater matrix feed and return, and on many engines the lines to the throttle body, turbo or oil-to-coolant exchanger. Blue silicone hose in bores from 6 to 32 mm is listed by length, alongside pre-formed heater hoses for particular cars.

Small hoses run hot and get little attention, yet a split heater hose can empty the cooling system just as surely as a burst radiator hose. Silicone keeps its flexibility through heat cycles that harden rubber, which counts near the exhaust or turbo, where small hoses often run.

Straight hose bent too tightly kinks and chokes the flow, so use a pre-formed bend or a metal elbow where the route turns sharply. On some engines the heater circuit is also the coolant bypass or the main bleed path. A heater delete there needs a loop that keeps coolant moving, not a blanked port.

Measure the spigot, then choose the bore and length.

• Bore: 6, 8, 10, 13, 16, 19, 22, 25 and 32 mm. The hose’s inside diameter should match the spigot’s outside diameter for a tight seal.
• Length: straight hose in 25 m rolls for 6 to 10 mm, 10 m lengths for 13 to 19 mm and 5 m lengths for 22 to 32 mm.
• Vehicle-specific hoses: pre-formed heater hoses listed by car in the title, shaped to the original route.
• Use: the smaller bores share sizes with fuel and breather hose, but silicone swells in fuel and oil, so keep it on coolant and air lines.

Cut the hose square with a sharp blade, push it fully over the spigot’s bead, and fit a clamp sized to the hose’s outside diameter just behind the bead. Clip long runs so they cannot rub on edges or touch the exhaust. Bleed the heater circuit with the heater valve open, because trapped air there shows up as a cold heater and erratic temperature readings.

At each service, squeeze the small hoses along their length. A hard, cracked or swollen section is due for replacement, along with its clamps.