Originally Posted by Wolf359
Originally Posted by spk2000
Originally Posted by Audios
DOT 3 is less likely to absorb water and can usually go longer in the system before changing. However 4 is the better fluid.
Have heard this more than once but never saw anything that proves it is true and not just rumor. Anyone got some studies or evidence?
I heard that as well, further research seems to show that Dot 4 actually absorbs less water than even Dot 3 so that bit isn't even true. The more frequent flush recommendation may just be a good reason for some dealer to get the car in for maintenance.
Not proof, just an old, oft' linked article: http://www.stoptech.com/technical-support/technical-white-papers/brake-fluid It's tough for me to accept either quote, based of anecdotal success stories using Valvoline Dot 3/4.
"DOT 4 fluids are also glycol ether based, but have a measure of borate esters added for improved properties including increased dry and wet boiling points. A seldom talked about characteristic is that because of this chemistry, the DOT 4 fluid will have a more stable and higher boiling point during the early portion of its life, but ironically once the fluid does actually begin to absorb water its boiling point will typically fall off more rapidly than a typical DOT 3."
The author also throws out this bone to stir the pot: "One last note on the DOT ratings: Systems designed for a particular type of fluid (especially prior to the wide distribution and use of DOT 4 fluids) should continue to be filled with that fluid. For example, in a car that was delivered with DOT 3 fluid, the internal components of the system (seals, brake hoses, and fittings for example) were specifically designed and tested for compatibility with the chemical composition of DOT 3 fluid. Because the DOT 4 grade fluid typically contains a different chemical composition, compatibility of system components may be an issue. "
Originally Posted by spk2000
Originally Posted by Audios
DOT 3 is less likely to absorb water and can usually go longer in the system before changing. However 4 is the better fluid.
Have heard this more than once but never saw anything that proves it is true and not just rumor. Anyone got some studies or evidence?
I heard that as well, further research seems to show that Dot 4 actually absorbs less water than even Dot 3 so that bit isn't even true. The more frequent flush recommendation may just be a good reason for some dealer to get the car in for maintenance.
Not proof, just an old, oft' linked article: http://www.stoptech.com/technical-support/technical-white-papers/brake-fluid It's tough for me to accept either quote, based of anecdotal success stories using Valvoline Dot 3/4.
"DOT 4 fluids are also glycol ether based, but have a measure of borate esters added for improved properties including increased dry and wet boiling points. A seldom talked about characteristic is that because of this chemistry, the DOT 4 fluid will have a more stable and higher boiling point during the early portion of its life, but ironically once the fluid does actually begin to absorb water its boiling point will typically fall off more rapidly than a typical DOT 3."
The author also throws out this bone to stir the pot: "One last note on the DOT ratings: Systems designed for a particular type of fluid (especially prior to the wide distribution and use of DOT 4 fluids) should continue to be filled with that fluid. For example, in a car that was delivered with DOT 3 fluid, the internal components of the system (seals, brake hoses, and fittings for example) were specifically designed and tested for compatibility with the chemical composition of DOT 3 fluid. Because the DOT 4 grade fluid typically contains a different chemical composition, compatibility of system components may be an issue. "
