So, long time viewer.Preventive Maintenance
#1 Check brake fluid level
#2 Windshield fluid
#3 Tires pressure and wear
#4 Grease all hinges (doors ,front and back)
#5 Treat all the seals to #4. Retaining the elasticity
This vehicle is so amazing ,I think it may take a generation or so
to weed out the ICE component. Hopefully sooner.

SalisburySam | 18 settembre 2019

Every time you open the brake fluid reservoir you risk moisture getting into the fluid. I think there is a warning light for low fluid. True for most cars today.

JAD | 18 settembre 2019

The brake system, reservoir cap, is vented, so opening the lid doesn't introduce any risk unless it is raining or something. Air always circulates to allow for expansion.

danv2 | 18 settembre 2019

I just look at the level. You never know about those warning systems.

donharvey2323 | 18 settembre 2019

The brake fluid cap has a diagram in it so the fluid does not contact air. Brake fluid reservoirs are see-through so you can check the level without removing the cap.

rxlawdude | 18 settembre 2019

diagram > diaphragm

That could cause a lot of confusion in a Planned Parenthood clinic. :-)

JAD | 18 settembre 2019

Interestingly, after doing a decent amount of research, I could not get a definitive answer on this. All cars have a vent system, but how that system works seems to vary greatly. Some seem to just have a big hose near the top of the reservoir as an overflow/vent, most have a small hole in the cap, and some of those have a bladder. Some of the bladders are mainly to keep dust and debris out that gets through the tiny hole, and some appear to have an air tight bladder that expands and contracts as the temp changes and the pads wear.

I took the cap off my 3 and it didn't clarify much. I didn't see an obvious hole, but the threads appear to have 3 channels to vent air. There does seem to be a rubber bladder inside the cap, but I can't tell what the bladder does. It does not appear to be big enough to account for all the fluid loss of pad wear.

Basically, I would check the fluid level by looking through the reservoir, but not worry at all about taking the cap off occasionally. But that is just me and I do change the fluid regularly.