how to tellthe diff between DOT 3 & DOT 5 brake fluid

Clem Clement

Clem Clement

Well-known member
I'm is a squabble about how to tell the diff between DOT 3& DOT 5 brake fluid? Both are slippery to the feel. DOT3 is clear in the can (doesn't it turn red with use). DOT 5 is purplish. My nose is no good for smell.
 
Water will mix with the dot 3, it will not in the dot 5 if the dot 5 is silicone which is normally purple in color. There is a new glycol dot 5 out which is not silicone based.
 
Clem,
You answered your own question: DOT 3 is clear (or amber) and DOT 5 is purplish. DOT 3 can become dark brown after a few years in the hydraulic system.
 
John R said:
Clem,
You answered your own question: DOT 3 is clear (or amber) and DOT 5 is purplish. DOT 3 can become dark brown after a few years in the hydraulic system.
Click to expand...

In time the purple fades and DOT 5 will take on a yellowish color, some describe it as being straw colored.
 
Put one, either one in a small plastic cup. Drop several
drops of the other type in in the cup. If it's the same type
it will mix. If it's the other type it will form a ball. G.M.
 
2x G.M. response. Implied but not said - DOT 5 cannot be used in a system with earlier dot fluids without a full flush with 5. DOT 5 is expensive so we used it only in our race cars that truly needed it. IMHO DOT 5 is unnecessary in any vintage street car.
 
DOT 5 or 5.1 is the best thing since sliced bread for an old car. No corrosion, no paint eating. I won't use anything else.
 
Curt in AZ said:
2x G.M. response. Implied but not said - DOT 5 cannot be used in a system with earlier dot fluids without a full flush with 5. DOT 5 is expensive so we used it only in our race cars that truly needed it. IMHO DOT 5 is unnecessary in any vintage street car.
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DOT 5 does keep most of the moisture out of the system. If bleed
annually I think it will keep all out. G.M.
 
If you don't want to use dot 5, in my experience dot 4 is better than dot 3. Dot 4 can be added to, or used to flush through a system that previously held dot 3.

Mart.
 
Here is what a bud sez:
Spill some water on the floor of you garage, put a drop of Dot 5 in the middle ,if the Dot 5 fluid pushes the water a way, it Dot 5.
 
Dot 5 and dot 5.1 are not the same. Dot 5 is harder to get, more expensive and in my opinion pointless in a regulary maintained automobile. I've found the pedal feel with dot 5 is not as firm as dot 3 or 4.
Agree with Mart dot 4 is great.
dot 5 normally purple as above and won't mix with water, it'll ball up and seperate, as above. Dot 5 is not compatible with any other dot brake fluid I believe, certainly not 3 or 4.
Silcon has no place in an establishment that does car body work. It's evil.

Martin.
 
Kahuna said:
DOT 5 or 5.1 is the best thing since sliced bread for an old car. No corrosion, no paint eating. I won't use anything else.
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DOT 5.1 will eat paint.

It is a glycol-based fluid, like DOT 3 and 4, and is not compatible with DOT 5. It is compatible with DOT 3 and 4.

The differences between DOT 3, 4, and 5.1 are primarily performance based. Those in the higher number categories usually have higher dry and wet boiling temperatures. Not really something of concern for a car that would be the subject of the Ford Barn.
 
I have found that when using any type of silicone brake fluid in a vintage car application you will never achieve a good hard pedal. It will always be mushy. As mentioned earlier that silicone brake fluid is good for racing applications .
Vic
 
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