Wait until the engine is cold before starting this procedure. Do not allow antifreeze to come in contact with your skin, or with the painted surfaces of the car. Rinse off spills immediately with plenty of water. Never leave antifreeze lying around in an open container, or in a puddle in the driveway or on the garage floor. Children and pets are attracted by its sweet smell, but antifreeze can be fatal if ingested.
Cooling system draining
With the engine completely cold, cover the expansion tank cap with a wad of rag, and slowly turn the cap anti-clockwise to relieve the pressure in the cooling system (a hissing sound may be heard). Wait until any pressure in the system is released, then continue to turn the cap until it can be removed.
Unscrew the bleed screw from the top of the hose junction above the expansion tank. Some models are equipped with a bleed screw adjacent to the oil filter cap
Unscrew the bleed screw (arrowed)
On some models, a second bleed screw is located adjacent to the oil filter cover (arrowed)
Undo the retaining bolts/clips and remove the undershield from beneath the engine
Engine undershield bolts (arrowed)
Position a suitable container beneath the drain plugs on the base of the radiator and the expansion tank. Unscrew the drain plugs and allow the coolant to drain into the container
Open the expansion tank drain plug (arrowed) . . .
. . . and the radiator drain plug
To fully drain the system, also unscrew the coolant drain plug from the right-hand side of the cylinder block and allow the remainder of the coolant to drain into the container. On N42 and N46 4-cylinder engines, a second block drain plug is fitted to the left-hand side of the cylinder block
The cylinder block drain plug is located on the right-hand side (arrowed)
On N42 and N46 4-cylinder engines, a second engine block drain plug is located on the left-hand side (arrowed – engine removed for clarity)
If the coolant has been drained for a reason other than renewal, then provided it is clean and less than two years old, it can be re-used, though this is not recommended.
Once all the coolant has drained, refit the bleed screw to the hose junction. Fit a new sealing washer to the block drain plug and tighten it to 25 Nm (18 Ibf ft).
Cooling system flushing
If coolant renewal has been neglected, or if the antifreeze mixture has become diluted, then in time, the cooling system may gradually lose efficiency, as the coolant passages become restricted due to rust, scale deposits, and other sediment. The cooling system efficiency can be restored by flushing the system clean.
The radiator should be flushed independently of the engine, to avoid unnecessary contamination.
To flush the radiator, disconnect the top and bottom hoses and any other relevant hoses from the radiator.
Insert a garden hose into the radiator top inlet. Direct a flow of clean water through the radiator, and continue flushing until clean water emerges from the radiator bottom outlet.
If after a reasonable period, the water still does not run clear, the radiator can be flushed with a good proprietary cooling system cleaning agent. It is important that their manufacturer’s instructions are followed carefully. If the contamination is particularly bad, insert the hose in the radiator bottom outlet, and reverse-flush the radiator.
To flush the engine, remove the thermostat, then temporarily refit the thermostat cover.
On completion of flushing, refit the thermostat and reconnect the hoses.
With the top and bottom hoses disconnected from the radiator, insert a garden hose into the radiator top hose. Direct a clean flow of water through the engine, and continue flushing until clean water emerges from the radiator bottom hose.
Cooling system filling
Before attempting to fill the cooling system, make sure that all hoses and clips are in good condition, and that the clips are tight and the radiator and cylinder block drain plugs are securely tightened. Note that an antifreeze mixture must be used all year round, to prevent corrosion of the engine components (see following sub-Section).
Slacken the bleed screw(s)
(see illustration 14.2a and 14.2b)
Turn on the ignition, and set the heater control to maximum temperature, with the fan speed set to ‘low’. This opens the heating valves.
Remove the expansion tank filler cap. Fill the system by slowly pouring the coolant into the expansion tank to prevent airlocks from forming.
| 1796 cc (engine codes N42 B18 and N46 B18)
| 1895 cc (engine code M43TU B19)
| 1995 cc (engine codes N42 B20 and N46 B20)
|6-cylinder engines (engine codes M52TU and M54)
||Long-life ethylene glycol based antifreeze*
|* Refer to your BMW dealer for brand name and type recommendations
If the coolant is being renewed, begin by pouring in a couple of litres of water, followed by the correct quantity of antifreeze, then top-up with more water.
As soon as coolant free from air bubbles emerges from the radiator bleed screw(s), tighten the screw(s) securely.
Once the level in the expansion tank starts to rise, squeeze the radiator top and bottom hoses to help expel any trapped air in the system. Once all the air is expelled, top-up the coolant level to the MAX mark and refit the expansion tank cap.
Start the engine and run it until it reaches normal operating temperature, then stop the engine and allow it to cool.
Check for leaks, particularly around disturbed components. Check the coolant level in the expansion tank, and top-up if necessary. Note that the system must be cold before an accurate level is indicated in the expansion tank. If the expansion tank cap is removed while the engine is still warm, cover the cap with a thick cloth, and unscrew the cap slowly to gradually relieve the system pressure (a hissing sound will normally be heard). Wait until any pressure remaining in the system is released, then continue to turn the cap until it can be removed.
The antifreeze should always be renewed at the specified intervals. This is necessary not only to maintain the antifreeze properties, but also to prevent corrosion which would otherwise occur as the corrosion inhibitors become progressively less effective.
Always use an ethylene-glycol based antifreeze which is suitable for use in mixed-metal cooling systems.
Before adding antifreeze, the cooling system should be completely drained, preferably flushed, and all hoses checked for condition and security.
After filling with antifreeze, a label should be attached to the expansion tank, stating the type and concentration of antifreeze used, and the date installed. Any subsequent topping-up should be made with the same type and concentration of antifreeze.
Do not use engine antifreeze in the windscreen/tailgate washer system, as it will damage the vehicle paintwork. A screenwash additive should be added to the washer system in the quantities stated on the bottle.