Quote Originally Posted by Greg Amy View Post
When you boil brake fluid, the pedal usually goes right to the firewall -- THUNK! -- and you can pump it back up, though the pedal feels "spongy". Each time you hit the pedal after that it wants to go to the firewall again, and you'll have to pump it back up. It feels similar to when you're bleeding the brakes and someone opens the valve. And, when you subsequently bleed the brakes after boiling the fluid, you'll see air in the lines (air that boils out of the fluid is not re-absorbed.)

This is a distinctly different feeling from "brake pad fade", which is when you exceed the optimal temperature of the pad compound you're using. In that case you'll feel the brake pedal get longer and spongier, and the transition to the firewall is usually slower and longer. Unless you completely explode the pads, you'll rarely get a THUNK! moment with pad fade.

This should also not be confused with pad "kickback", where variations in rotor, bearing, or wheel "true-ness" - or even spirited hits over curbs - cause the caliper pistons to move back into the caliper a bit too far, forcing you to have to pump the brakes to get the piston back in position against the rotor (it's the reason you'll occasionally see a fast driver lightly tapping the brake lights a few times along the straights). The difference there is that when you do pump up the brakes after kickback the pedal feels nice and hard again, versus a still-soft pedal in the case of boiled fluid.

Finally, you could buy temperature-sensitive paints or labels and stick them to your calipers. These devices change colors when a specified temperature is reached, allowing you to note how hot the calipers got. If the caliper temp is exceeding 600 degrees (for example), then you can be pretty confident your fluid is getting that hot, too.

Bottom line, though, Dan? It's not something to worry about at this point; it takes a lot of performance to boil brake fluid, and long before that happens you're gonna start slagging pads, rotors, and possibly even piston seals. Instead, take the time to ensure your brake system is in good shape, bleed the brakes properly and regularly, and just "shut up and drive".

Greg
This is the kind of information newer drivers and rookie crew chiefs really need. This info is much appreciated, Thanks