Most BMW 550, 650, 750 i engines did or will develop a common coolant leak which perhaps resembles a funny slightly stinky smell in the cabin, in turn could escalate to an electrical burning smell over time.
The burning electrical smell could be your alternator being damaged by coolant leaking into it.
Always check inspect the turbocharger cooling lines passing right above the alternator or you will be replacing the lines – hoses and plus the alternator as well, at the same time.
This is not an easy job, due to the dual turbo arrangement in the middle of the engine block V configuration.
Performing a pressure test after repairs is essential due to system complexity. Both after run electrical pumps should be also tested to prevent turbo charger premature early failure.
There are additional lines under the alternator which should be also inspected with a fiber optic camera to ensure system reliability and performance in the long term.
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