Does the type (DOT#) of brake fluid used matter all that much?

I recently changed my brakes and had to bleed a small amount of brake fluid in the process. I topped off the brake fluid reservoir with some DOT3 brake fluid. I did not notice until the next day that it asks for DOT4 brake fluid. This vehicle is my daily driver and won't be tracked.

2/9/2009 3:24:17 PM

                      DOT 2 	DOT 3 	DOT 4  	DOT 5
Dry Boiling point 	374 	401 	446 	500
Wet boiling point 		284 	311 	356

[Edited on February 9, 2009 at 3:30 PM. Reason : all in °F

2/9/2009 3:28:59 PM

What you really need to know is this:

DOT 3 and DOT4, and to some extent DOT 5.1 will all mix, as they are glycol based. That's the crucial part. DOT 5 is silicone based, and doesn't mix effectively with glycol.

Also...the glycol fluids are incompressible, and exhibit hygroscopic behavior (the extent depends on the fluid). Silicone fluid absorbs NO water; if any moisture condenses in the system, it can pocket and creat localized corrosion problems. Silicone fluid also has a small degree of compressibility. So if you want a rock-hard pedal, the hell with that.

2/9/2009 3:53:28 PM

interesting. i just wanted to know if it was crucial to use what was recommended. i want to avoid having to bleed the entire brakes, for now at least.

2/9/2009 5:00:29 PM

was the bottle that you used to top it off sealed?

2/9/2009 5:12:59 PM

I believe DOT 3, 4 can mix together...so yes you should be fine.

DOT 5 is in its own world and can't mixed.

2/9/2009 11:17:21 PM

^what made you think that you needed to post, since 7.5 hours ago zx posted the exact same thing without the lack of confidence that your post exhibited.

2/9/2009 11:29:50 PM

FUCKING OWNED

2/10/2009 7:56:19 AM

BAM

2/10/2009 7:57:43 AM