Check points under the hood (BMW 3 Series E46)

4-cylinder engine (2.0L engine shown)
A - Engine oil level dipstick
B - oil filler cap
C - expansion tank of the cooling system
D - brake and clutch fluid reservoir
E - windshield washer reservoir

6-cylinder engine (2.5L engine shown)
A - Engine oil level dipstick
B - oil filler cap
C - expansion tank of the cooling system
D - brake and clutch fluid reservoir
E - windshield washer reservoir