[Blown353]

Fade is not the issue with DOT5-- it's boiling off the moisture that gets trapped in the lowest point in the system. If there is an appreciable amount of moisture in the system (it will take time) and you get the brakes hot, it will boil and you won't have ANY brakes. With a standard Dot 3/4/5.1 brake fluid the moisture is evenly absorbed resulting in a gradual lowering of the boiling point as the overall percentage of moisture suspended in the fluid increases. With DOT 5 you get big pockets of water at the low spots which boil around 212F which is much lower than even the moisture saturated boiling point of a good 3/4/5.1 fluid.

I've boiled brake fluid several times in different cars and the worst cases involved DOT5 in friend's street rods (who put the fluid in because they didn't want to damage their super-nice painted engine compartments.) Also, with DOT5 my experience is the pedal will get "spongier" if you drive into higher altitude than where the system was filled because the difference in atmospheric pressure causes the bubbles in the fluid to grow. Driving from here (15' above sea level) up to Reno (about 4400') resulted in a very soggy low pedal in a friend's 32 Roadster... which was somewhat squishy to start with because of the nature of DOT5.

I've seen the inside of calipers of DOT5 systems after prolonged fills without flushing; they were rusty in the bottom from pooled moisture which caused the seals to leak and thus prompted the replacement.

One point of note: I don't believe any OEM out there uses DOT5 as a factory-fill in their brake systems. That's a very important piece of data IMO. In fact, the only non-DOT 3/4/5.1 factory fills I have ever seen in a car is some Bentleys which use mineral oil (which is also shared with the load levelling suspension) but that is a very oddball atypical setup.

If you're having good luck with DOT5, cool. I for one have had too many negative experiences with it and after some research and a decent understanding of the moisture interaction properties of DOT5 I will never use it in any of my vehicles from a safety standpoint. Keeping the paint pretty under the hood is much less of a concern to me than having my brakes work when I need them. I'm a big propnent of using a good 3/4/5.1 fluid and doing flushes at least yearly or prior to any track event where you'll be using the brakes very hard for sustained periods of time.