E46 RADIATOR SWAP

Our first task is to remove the relevant underbonnet plastics – N42 and N46 models have one front cover and another on top of the main engine. They’re held on with a couple of plastic rivets and 10mm nuts, so they’re off in a few seconds.

Now we need to remove the airbox assembly. On most E46s, there are two 10mm bolts, as well as a large hose clip securing the intake bellows to the throttle body. On these cars, the MAF is built into the airbox, so there’s a vacuum hose and electrical connector to unplug.

In this photo, the fat hose is for the engine air pump and this can either be swung out of the way or removed completely. There’s also a small electrical plug to disconnect – pictured here on the bottom hose; mark it for reference if necessary.

This relay unit sits on top of the radiator fan cowling and has to be carefully unclipped to avoid breaking the retaining lug – nothing Araldite won’t fix. Once unclipped from the cowling, either remove it or tie it out of the way.

Two things of note in this photo are the big multi-connector plug for the electric fan (you won’t have one on automatic gearbox cars with the six-cylinder engine) and the small Torx screw (circled) securing the fan housing to the radiator.

After that Torx screw is removed, the fan can be lifted out. It’s hard to see, but the under-radiator coolant tube hooks into the side of the rad and is secured to the fan cowling with a pair of plastic rivets. Viscous fan? You’ll need a big 32mm spanner – and it’s a reverse thread. Push-fit hoses can be a challenge to remove, especially after 15 years. You’ll need a big drain bucket underneath to catch escaping coolant, then hook the clip upwards with a screwdriver and wiggle the hose until it’s free. Catch the O-ring if it falls out. As in Step 7, disconnect the top rad hose from the engine coolant stub – the smaller bore hose to the right of the top hose also needs to be disconnected. Don’t lose the metal hose clips as they are not available separately from BMW. The rad expansion bottle doesn’t come off easily. Start by pulling up both the pictured clip and the smaller one next to it, just out of shot. Use a flat-blade screwdriver and a shot of penetrating fluid to help it along.

This hose also needs to be disconnected from the oil-to-coolant heat exchanger. These can rupture internally, leading to oil in the coolant – if there are traces of oil in the coolant, examine this part carefully and replace it. A very simple job.

The expansion tank can now be pulled up and out, but it’s often difficult. This photo shows the base of the expansion tank with the two-port coolant baseplate fitted. Note the plastic and wire hook at the top – pull it out and the tank comes off…