Difference between DOT 3 and DOT 4

imported_Barry Wolk · February 5th, 2006

I'm about to fill the brake system on the trailer and I want to know the difference between DOT 3 and DOT 4 fluid. The manufacturer does not recommend DOT 5.

Bob Kinker · February 5th, 2006

Dot 3 is regular old brake fluid. Dot 4 is semi synthetic. Doesn't absorb as much moisture. I use Dot 4 in all of mt antiques that have hydraulic brakes. No problems.

Joe_Materasso · February 5th, 2006

Quote:

I'm about to fill the brake system on the trailer and I want to know the difference between DOT 3 and DOT 4 fluid. The manufacturer does not recommend DOT 5.

DOT 4 has a higher boiling point also; DOT 5 is silicone based and has a distinctive purplish hue, and is definately NOT compatible with all braking systems!

Happy Motoring!

jm

De Soto Frank · February 6th, 2006

DOT 4 is interchangeable with DOT-3, but has more corrosion inhibitors...I've been using DOT-4 in my last couple of full brake rebuilds.

Only time will tell as to its long-term effectiveness !

Follow your mfr's advice about the DOT-5...