Originally Posted By: E150GT
Originally Posted By: philipp10
I have been saying it for years (but no one will listen) that a well designed brake system will keep the fluid dry. Furthermore, even if water gets in the fluid, unless your in the mountains or towing, your not going to boil the fluid. I never bleed my brakes yet have never replaced a caliper. Go figure.
If you keep your car for only a few years this is correct. Why change it? If you keep it for a long time, change it regularly. Your brake system corrodes from within and you can’t see it and one day it will fail you. Mine did and luckily I was in a parking lot. I would have been in deep kimchi had I been on the highway.
Technically not correct. Brake fluid will absorb moisture from the air and that's from when they heat up and cool down. So moisture gets in through the brake lines and through the rubber from the calipers. OP won't notice any difference in braking between Dot 3 and Dot 4 as they're both liquids. The difference is in the spec, Dot 4 has a higher boiling point than Dot 3, but if the brakes never get near that temperature, then it doesn't matter. Mercedes tends to use a Dot 4+ fluid and they require brake bleeds every 2 years as Dot 4 is more hygroscopic than Dot 3. What happens is that if you don't bleed the brakes, you end up with the wet boiling temperature spec instead of dry boiling temperature. For instance my Pentosin super dot 4 has a dry boiling temp of 509 but the wet boiling temp is 329. So if you don't hit 329, your brakes will be fine even if you don't flush them and they're filled with water, but if you're towing or coming down a mountain and heat up the brakes, they may disappear when the liquid turns into a gas. Dot 3 has lower numbers, 401 dry and 284 wet.