UNDERBONNET CHECKS & FILTERS

1 FIND THE AIR FILTER

Prise off the engine cover to reveal the air filter housing. Undo the Jubilee clip on the offside of the engine bay that secures the induction pipe to the MAF sensor and air filter housing. Detach the electrical plug at the MAF sensor.

2 REMOVE FILTER HOUSING

Detach the induction feed pipe between the nearside front of the engine (it’s secured to the front slam panel) and the air filter housing. Lift the air filter housing off its four mounting points by prising them away. Remove the air filter housing from the engine bay.

3 SOUND-DEADENING

Undo the couple of screws that secure a sound-deadening panel and material over the top of the engine. Manoeuvre the panel out of the engine bay – it’s quite awkward to remove and just as hard to refit. In our case, some of the sound-deadening material had broken off.

4 REMOVE AIR FILTER

With the air filter housing away from the engine bay, release the series of metal spring clips to open the lid, but be careful not to break the lid’s hinges along the back of the housing – don’t force the lid open. Remove the old air filter and check the new one is the same size and shape. We fitted a Bosch air filter supplied by CAAR, which costs £29.50.

5 REPLACE AIR FILTER

Before fitting the new air filter, remove any dirt from inside the air filter housing. In our case, dried leaves and other debris had collected, so we removed these by hand before installing the new air filter and then refitting the lid. We had to squeeze it shut before the spring clips could be refitted.

6 CRANKCASE BREATHER

BMW recommends renewing the crankcase breather, although it’s not listed on their service schedule. The breather is located on the top of the engine and requires the air filter housing and sound deadening material to be removed. Start by undoing its three 5mm Allen key mounting bolts and the small Torx E6 bolt, circled here.

7 REPLACE BREATHER & SEAL

After undoing the three 5mm Allen key mounting bolts (they cannot be extracted), carefully detach the breather from its frontmost pipe and lift it out. Extract the seal left behind – there’s a tag on it to help removal. Spray a light grease over the new seal and fit it with the new breather, progressively tightening all 5mm Allen key mounting bolts and the Torx E6 bolt.

8 CHECK COOLANT LEVEL

Make sure the engine is cold, then release the coolant expansion tank’s pressure cap on the nearside of the engine bay and check the level inside. There’s a ‘MIN’ and ‘MAX’ indicator to help show whether the coolant needs topping up. Use whatever type of coolant has been used before.

9 TEST THE COOLANT

It’s a good idea to use an antifreeze hydrometer to monitor the freezing point of the engine’s coolant. When refitting the pressure cap, wind it on until the arrow on the top of the cap lines up with an arrow on the top of the expansion tank. The cap will need to be wound several times to fully fit.