DOT 4 or DOT 3

[stevelp]

Just changed the fluid in both brakes and the clutch. All they had at the parts store was DOT 3 synthitic brake fluid.  What is the difference in DOT 3 and DOT 4?  Can either one be used?

[OP2]

The synthetic brake fluid that I have seen excedes dot 3 and 4 fluid requirements. I know that dot 4 is required in our systems. I too have just replaced the brake fluids with synthetic fluid.

[MP]

Use 4.  I do not believe 3 is compatible!

MP

[Old Geezer Richard]

 I have use dot 3-4 on the Valk and on my two El Camino's and Chevy van with no problem providing that you flush out all of the other fluid completly ... you don't want to use dot 3 or dot 4 and mix it with the dot 3-4 its a either or ........ I believe that the higher you go on the number scale with dot fluids it has a higher flash point and does not attract moisture as much ...... but from what I understand the full synthetic fluid is the best ...... alot of folks who have real old cars that they do not drive much only in parades or car shows use the full synthetic because it does not attract the moisture and break down quickly ....... this is what I have heard ....

[9Ball]

Use 4.  I do not believe 3 is compatible!

MP

DOT 3, 4, and 5.1 are compatible.  DOT 5 is not compatible with any of these.  AVOID DOT 5.

Synthetic is often labeled DOT3/DOT4 and is a great choice for the Valk.  Synpower is a brand name readily available at the auto parts stores in our area.

[Robert]

The boiling point is the difference in the fluids all are basically the same except for dot 5 that is silicon and cannot be mixed with any other fluid. The correct fluid to use is dot 4 usually 3 is for disc/drum combinations


DOT 3     401ºF     284º F
DOT 4    446º F    311º F
DOT 5    500º F    356º F
DOT 5.1    518º F    375º F

[Tx Bohemian]

The boiling point is the difference in the fluids all are basically the same except for dot 5 that is silicon and cannot be mixed with any other fluid. The correct fluid to use is dot 4 usually 3 is for disc/drum combinations


DOT 3     401ºF     284º F
DOT 4    446º F    311º F
DOT 5    500º F    356º F
DOT 5.1    518º F    375º F

Maybe it's too early on this Monday morning and the ol brain just ain't working yet but why are there two different temps on each one of these?

[Robert]

Sorry should have put that in, its the wet or dry boiling point. Brake fluid is hygroscopic which means that it absorbs water. When this happens it turns color and lowers the boiling point and this is the way that it is designed to do. Why? because in the brake system between air in the reservoir and condensation in the system you get water in it. This water can corrode the system in that one spot and also the water sitting in the system can boil and cause air and steam this of course causes no brakes so the fluid is meant to absorb the water and hold it so you can eliminate it out of the system when you do a flush. This is the problem with silicon fluid that is doesn't absorb water.