Introduction
Brake fluid is what is called HYDROSCOPIC/HYGROSCOPIC this means "Having the ability to absorb moisture from the atmosphere." if you get a small amount of brake fluid in a container it will be completely clear... add a drop of water and you will see it turn a milky colour... add enough water and it will all turn milky.
This is due to their chemical make up DOT3,4 & 5.1 are polyethylene glycol-based they can be mixed with each other (ie uprating from DOT 3 to DOT 5.1) it doesnt matter if there is some DOT 3 left in the system when using 4 and 5.1.
DOT 5 on the otherhand is silicone based and SHOULD NOT be mixed with DOT 3,4 or 5.1. DOT 5 is mainly used in classic applications as it doesnt strip paintwork. DOT 5 isnt hydroscopic but if any moisture is introduced it will find its way to the lowest point of the system corroding brake parts or worse boiling off if the temperature rises.
Minimal boiling points for these specifications are as follows (wet boiling point defined as 3.7% water by volume):
Boiling point ranges
'Dry' boiling point 'Wet' boiling point
DOT 3 205°C (401°F) 140°C (284°F)
DOT 4 230°C (446°F) 155°C (311°F)
DOT 5 260°C (500°F) 180°C (356°F)
DOT 5.1 270°C (518°F) 191°C (375°F)
As you can see when water is introduced the boiling point rapidly decreases a caliper can easily reach 140°C under heavy braking which isnt good as you will loose almost all braking ability.
Also a note on DOT 3/4/5.1. The worst thing for your system is moisture, and DOT 3 or 4 or 5.1 attract this. They have inhibitors which turn the fluid golden and then to a light brown before they are used up and the fluid needs to be flushed. The fluid should be checked for color and if it's darker than honey, flushed and replaced. If it's black you really need to do a complete teardown of the system and see what has corroded and replace it before continuing.
*some info taken from DOT3 and DOT5 pages in wikipedia*
*I cannot guarantee the accuracy of the information in this document nor do I take any responsibility for damage to any vehicle or person due to the misinterpretation of the information/inadequate skills, any work that you carry out to your own vehicle is entirely at your own risk. These are guidelines only and if in doubt I kindly suggest that you contact a Fiat dealer/relative organisation for clarification/legalities.*
Brake fluid is what is called HYDROSCOPIC/HYGROSCOPIC this means "Having the ability to absorb moisture from the atmosphere." if you get a small amount of brake fluid in a container it will be completely clear... add a drop of water and you will see it turn a milky colour... add enough water and it will all turn milky.
This is due to their chemical make up DOT3,4 & 5.1 are polyethylene glycol-based they can be mixed with each other (ie uprating from DOT 3 to DOT 5.1) it doesnt matter if there is some DOT 3 left in the system when using 4 and 5.1.
DOT 5 on the otherhand is silicone based and SHOULD NOT be mixed with DOT 3,4 or 5.1. DOT 5 is mainly used in classic applications as it doesnt strip paintwork. DOT 5 isnt hydroscopic but if any moisture is introduced it will find its way to the lowest point of the system corroding brake parts or worse boiling off if the temperature rises.
Minimal boiling points for these specifications are as follows (wet boiling point defined as 3.7% water by volume):
Boiling point ranges
'Dry' boiling point 'Wet' boiling point
DOT 3 205°C (401°F) 140°C (284°F)
DOT 4 230°C (446°F) 155°C (311°F)
DOT 5 260°C (500°F) 180°C (356°F)
DOT 5.1 270°C (518°F) 191°C (375°F)
As you can see when water is introduced the boiling point rapidly decreases a caliper can easily reach 140°C under heavy braking which isnt good as you will loose almost all braking ability.
Also a note on DOT 3/4/5.1. The worst thing for your system is moisture, and DOT 3 or 4 or 5.1 attract this. They have inhibitors which turn the fluid golden and then to a light brown before they are used up and the fluid needs to be flushed. The fluid should be checked for color and if it's darker than honey, flushed and replaced. If it's black you really need to do a complete teardown of the system and see what has corroded and replace it before continuing.
*some info taken from DOT3 and DOT5 pages in wikipedia*
*I cannot guarantee the accuracy of the information in this document nor do I take any responsibility for damage to any vehicle or person due to the misinterpretation of the information/inadequate skills, any work that you carry out to your own vehicle is entirely at your own risk. These are guidelines only and if in doubt I kindly suggest that you contact a Fiat dealer/relative organisation for clarification/legalities.*
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