Also known as: n52b25, n52b30, 3.0 straight-six, 328i engine, magnesium six
The naturally aspirated straight-six of BMW's mid-2000s range, in 2.5 and 3.0 litre forms — the last of the line before turbocharging took over, and widely regarded as one of the most durable engines the company has built. Its distinguishing feature is a magnesium-alloy block casting around an aluminium core, which made it unusually light and is also why it is unforgiving of overheating.
Because it is port-injected and naturally aspirated, it has none of the direct-injection carbon or high-pressure fuel problems its successors brought. The faults it does have are age and gasket faults: the valve-cover gasket and the oil-filter housing gasket both harden and weep, and on this engine the leak commonly reaches the alternator below it — an alternator that fails on an N52 is worth inspecting for oil contamination before it is simply replaced.
The electric water pump and its thermostat are the other consumable, and failure is typically sudden rather than gradual. Valvetronic's eccentric-shaft sensor is the one electronic fault worth knowing, since it produces limp behaviour that reads like a throttle problem.
Cars fitted with this engine
12 generations, across 1 make. From the authored catalogue — an absent car means the catalogue has not reached it, not that the engine was never fitted.
Information, not instruction
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