Cooling System: Bleed Procedure

Words and Pictures: Dave Livingstone

Ensuring that the cooling system is clear of all air is essential: air bubbles act as highly efficient 'plugs' to impede water flow. If this happens, the engine can over heat - which could mean failure of the head gasket - or even more expensively, warping of the alloy engine castings. Here Dave sets out the basic bleed procedure (Dieter has some excellent instructions on how to achieve this too - linked here).

1 Mix required amount of coolant and water in a 50:50 solution – the system holds 10 litres of mixture in total.
2 Remove the expansion bottle cap and fill the expansion bottle to the top with coolant.
3 Open all of the three bleed points:
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a. Heater matrix bleed screw (located on front bulkhead in front bonnet compartment)

b. Radiator bleed screw (located on right of bonnet closing panel)

c. Heater Bypass/Return bleed screw (located on the right side of the engine)

[Dave indicates that all three bleed screws should be open at the same time - and this is how the workshop manual states the way it should be done, however, I usually open one at a time if working on my own so excess fluid doesn't run out - Rob]
4 As coolant starts to flow out of each bleed point at a constant rate, close the bleed screw. You shouldn’t find that the expansion bottle empties before this happens, but keep an eye on it and top it up if necessary. [It may be helpful to have a willing assistant to help out with this - Rob]
5 Fill the expansion bottle back up and screw the expansion bottle cap back on securely.
6
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Turn the heater to the maximum hot position.
7 Start the engine.
8 Check for leaks around the car, particularly the clips on the hose.
9 After 20 – 30 mins the engine should have reached normal working temperature and the radiator fan should come on. Switch off engine.
10 Open each bleed point to allow any trapped air to escape. As soon as coolant runs freely from a bleed point close it.
11 Tighten all the bleed points:

a. Radiator bleed screw (Torque to 5 Nm)

b. Heater matrix bleed screw (Torque to 7 Nm)

c. Heater Bypass/Return bleed screw (Torque to 5 Nm)
12 Allow the engine to go completely cold.
13 Check the coolant level in the expansion bottle. Top up or remove fluid until the coolant level is at the maximum mark – the higher of the two plastic ledges that can be seen inside the expansion bottle on the side nearest the back of the car.
14 Ensure that the expansion bottle cap is securely screwed back on.
15 Repeat steps 6 to 11 above for 100% confidence that there is no air in the system.
16
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Last check: ensure that the coolant level is at 'max' mark on expansion tank, and top up if necessary.