Yes, DOT3 and DOT4 are completely interchangeable. Dot5 is NOT, but very few vehicles use DOT5.

The difference is simply the boiling point of the brake fluid. DOT3 will have a lower boiling point than 4, and 4 lower than 5. In high performance applications, the brake fluid can boil under the severe heat of hard braking, which causes brake fade or complete failure.

On a side note, DOT5 can NOT be used in a system with rubber. All rubber brake lines must be changed to stainless steel braided lines.

 

The braiding wouldn't matter. The composition of the hose under the braiding would be the determining factor.

 

They are compatible. Have you flushed that 6 year old fluid? If not it's overdue. l do mine every 3 years with ATE dot 4. Trust me, you will notice the difference.

 

No I haven't and was going to bleed the brakes (replace old with new throughout the lines). Also planned on replacing brake pads/rotors (1st time changing) but then I read this:

http://www.tundratalk.net/forums/maintenance-repair/100285-rear-brake-job-w-new-rotors.html

Bleeding not recommend. Huh? I'm confused.

 

As stated, its OK to use DOT 4 synthetic... DOT 5 is silicone based and will not work...

Some people get the two confused...