I didn’t have an E46 330 but did have a 325.
Fuel was pretty good – it mostly did longer trips (70 mile daily commute) and average 31.7mpg. Mine was a manual though but with a 5 speed box.
Running costs were fairly hefty, but I did 35k over the two years I had it.
In the time that I had it, I had:
2 pairs of rear tyres (circa £300 each time)
1 pair of front ttres
2 sets of rear springs
2 x rear shocks
2 sets for front wishbones
1 x thermostat
1 x radiator
1 x water pump
1 x coolant tank
1 x set of aux pulleys
1 x set of discs and pads
1 x set of new brake lines (expensive – fuel tank out jobbie)
1 x fuel pump
1 x Inspection 1
1 x Oil service
1 x brake fluid change
The cooling system on this era of BMW are notoriously weak – the plastic impellor on the fule pumps fail, the thermostats fail, coolant tanks split and the bottoms of radiatiors sag.
They also eat suspension parts – cracked rear springs are pretty common and wishbones are a consumable / disposable item.
They are really sensitive to wheel alignment too – a Kwik Fit jobbie isnt’t up to scratch. It needs to be a proper lazer four wheel one – BM will releive you of £250 or so (unless on offer) and a good indy about £100. Having tried to do it on the cheap, you’ll get a crap job.
The rear brake lines corroed and needed replacing which was quite pricey – they run over the fuel tank which needs to be dropped. This is quite a common issue on these now.
The only good news is that there are loads of good independent specialists that can help keep costs down. Second hand parts are plentiful too from the likes of Quarry Motors.
The biggest thing on the E46 these days is rust – they are notorious for rusting at the arches. From the inside out due to a silly lip that collects mud and water.
They are really good cars though – mine wasn’t the best and had had a hard life (think it was the familt run around). It drove nicelt though, was reasonably quick and sounded good.
If you do lots of short journeys, the auto may be a bit juicy. I currently have an E90 330 auto which does around 25mpg on short town trips but will happily do 33 or so on a longer run.