Cooling System Layout And Precautions

How The Circuit Is Laid Out

Every X-Type in this range runs a sealed, pressurised cooling circuit with a thermostat that decides when coolant may reach the radiator. An impeller pump moves the mix. On petrol and diesel alike the pump is belt-driven from a pulley on the front camshaft.

Petrol: the pump sits at the left-hand front of the engine and takes a short belt off the camshaft. Diesel: the pump bolts to the left-hand front of the block. The belt turns the power-steering pump pulley, and that pump drives the water pump through splines.

Petrol thermostat: in the return path from the block to the pump, left-hand front. Diesel thermostat: in a housing on the left-hand end of the block, under the brake vacuum pump. Coolant wraps the cylinders in the block and, in the heads, the cast galleries around the ports. While the engine is cold the thermostat stays shut, so flow bypasses the radiator and returns through the metal pipe across the front of the engine toward the radiator bottom hose. The heater take-off is from the rear of the thermostat housing. Once the thermostat opens, hot coolant goes through the radiator and back into the engine.

The radiator is aluminium with plastic end tanks. Automatic cars put the transmission fluid cooler in the left-hand end tank. Two electric fans sit behind the radiator. The system is closed by a pressure filler cap on the expansion tank: pressure lifts the boiling point and helps the radiator do its job. Hot expansion pushes surplus into the tank; as the system cools, that surplus is drawn back.

Some diesels carry an electric booster heater in the heater-matrix supply hose on the lower bulkhead at the rear of the bay. The ECU switches it when inlet-air temperature is near freezing. Three plugs in the housing give about 250 W each. Scandinavian-market diesels may instead use a fuel-fired booster that runs with the engine when ambient air is below about 5 C or coolant is below about 75 C.

Heating Side In Brief

Cabin heat comes from a blower and a matrix in the heater unit, fed by hoses off the engine circuit. Fresh air passes a pollen filter under the windscreen cowl. Electronically driven flaps steer the air. Climate-control cars show temperature, blower speed, demist and direction on a digital panel. Air conditioning is a separate sealed loop; see the A/C warning article before you touch any refrigerant fitting.

Hot Cap, Hot Fans, Antifreeze

Do not remove the expansion-tank cap, and do not open any joint, while the engine is hot. Scalding coolant and steam will find the gap. Wait until the tank and radiator are fully cold. If you must release residual pressure after a cool-down, lay a thick cloth over the cap, crack it slowly until it hisses, wait for the hiss to stop, then continue. Keep your face and hands clear of the opening the whole time.

Antifreeze burns skin and paint. Rinse spills with plenty of water. Do not leave open coolant where a child or animal can drink it.

With a hot engine the electric fans can start even though the engine is off. Hair, sleeves and tools stay clear of the shroud whenever you work in the bay after a run.