# Brake Fluid Compatibility **URL:** \ **Category:** Maintenance/Repairs\ **Created:** [June 28, 2016, 8:28pm UTC](https://community.cartalk.com/t/brake-fluid-compatibility/93682 "2016-06-28T20:28:45Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![jmcarc](https://avatars.discourse-cdn.com/v4/letter/j/278dde/32.png) [@jmcarc](https://community.cartalk.com/u/jmcarc)\ **Post date:** [June 28, 2016, 8:28pm UTC](https://community.cartalk.com/t/brake-fluid-compatibility/93682/1 "2016-06-28T20:28:45Z")
I recently replenished my supply of DOT3 brake fluid stored in my garage, but noticed the new bottle was labeled “DOT3 Synthetic”, made by STP. I don’t know what is meant by “synthetic”. Will there be any compatibility problems if I put this in my car that already has a non-synthetic DOT3 fluid? ---
**Author:** ![Mustangman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/mustangman/32/44130_2.png) [@Mustangman](https://community.cartalk.com/u/Mustangman)\ **Post date:** [June 28, 2016, 8:40pm UTC](https://community.cartalk.com/t/brake-fluid-compatibility/93682/2 "2016-06-28T20:40:03Z")
No, none. any DOT 3 can be mixed with DOT 4 or DOT 5.1 (glycol based) fluids but not DOT 5 (silicone based). BTW, all brake fluid is essentially “synthetic” or man made. Glycol doesn’t appear in nature. ---
**Author:** ![texases](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/texases/32/862_2.png) [@texases](https://community.cartalk.com/u/texases)\ **Post date:** [June 28, 2016, 9:11pm UTC](https://community.cartalk.com/t/brake-fluid-compatibility/93682/3 "2016-06-28T21:11:34Z")
The STP web site lists a DOT4 synthetic, but not a DOT3 synthetic. The major difference in the composition on the safety sheet (very complete) is the DOT4 had “Triethylene glycol monomethyl Borate Ester”, the DOT3 doesn’t. Like @Mustangman said, they’re compatible.