Dot 3 or Dot 4

[tommie b]

Hi and thanks in advance. Just rebuilt 58 Oldsmobile brake system with new power master dual res. New front disc calipers and new rear wheel clys. Would dot 3 or dot 4 should be used?

Don't want to use Dot 5. What would be best in this old car?

[Marty Roth]

Dot 4 is interchangeable with, and will mixwith Dot 3, but4 is better because it is less HYGROSCOPIC, meaning that is less likely to absorb moisture which ultimately causes rust in your brake system. I flush my brake systems (when I think about it) every 2 - 4 years, and replace with Dot 4.

 

I have had excellent success with Dot 5 which is silicone, and have never had a problem with it - but only after a COMPLTET REBUILD of the brake system, and flushing all hard lines with alcahol and replacing all hoses. 

[joe_padavano]

I concur with Marty.  I've also used DOT 5 silicone with no ill effects, but others have had problems.  DOT 4 is a better grade of conventional brake fluid and is preferred if you can get it easily.

[Curti]

I concur with Marty.  I've also used DOT 5 silicone with no ill effects, but others have had problems.  DOT 4 is a better grade of conventional brake fluid and is preferred if you can get it easily. P

 

+1 on the DOT 5   Put it in once for life.  And it doesn't take off the paint if  when I spill it.

[c49er]

DOT 4 has a higher boiling point.