Quote:
Originally Posted by SV650rules
Automotive brake fluid reservoirs have a vent in the actual lid, but below the lid is a flexible membrane that has a collar ( sometimes pressed down by the lid to seal better) that is a tight fit in the neck of the reservoir and the membrane will allow level in reservoir to rise or fall while sealing the fluid from the atmosphere... The pinhole vent in the actual lid is just to allow the air above the flexible membrane to equalise and not build up pressure or vacuum as the membrane does its job.
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Hmmm Ive never seen one of those in a car only on bikes and I assumed it was because theyre more exposed to the elements but maybe it depends on the manufacturer...