Not necessarily more total absorption for DOT 4, but they tend to absorb moisture at a higher rate. German cars take DOT 4 fluid, but require replacement every 2 years (in general), Asian cars take DOT 3 fluid, but only require replacement every 3 years. Stoptech has a good white paper on this: http://www.stoptech.com/technical-support/technical-white-papers/brake-fluid
Originally Posted By: Tay
i read that DOT 5.1 is much more hygroscopic then DOT 4 and DOT 4 more then DOT 3. is there any truth to this?
Originally Posted By: Stoptech
The real differentiating factor is that DOT 4 fluid should be changed more often than a DOT 3 fluid, because of the effects and rates of water absorption.