Let’s be clear up front – if your brake fluid has not been changed in over a year, you are past-due to replace it. Brake fluid is hygroscopic- it naturally absorbs water from humidity present in the air. Therefore, it requires regular maintenance.
This article is meant to help you make an informed choice when you hit the parts store.
A lot of technical innovations in automotive chemicals have been linked to better performance, increased engine or component life or a less toxic, more earth-friendly disposal for spent fluids. Brake fluid – the hydraulic liquid that is used to “push” your brakes when pressure is applied – has similarly gone through evolutionary development.
Very much like engine oil or power steering fluid, there are dozens of brake fluid choices at your local parts store. They carry everything from the store brand DOT 3 fluid costing a buck, to very high end synthetic fluids that may cost twenty dollars per can. Keep in mind, the same rules that apply to selecting engine oil apply to brake fluid: the more expensive option is not always the best option.
Some of the brake fluids available for racing applications might perform well when used in those conditions but might not be right for the street.
So, what is the difference between DOT 3, DOT4, DOT5 and most recently DOT5.1?