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?
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.