Mixing brake fluids? [Archive] - GrandAmGT.com Forum


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03-03-2005, 11:36 AM
Im a little low and I can no longer stand the stupid light coming on. Today I searched the garage for some brake fluid and found some Prestone DOT 3. Can I just dump some of this in to the already existing fluid thats in there?

03-03-2005, 11:51 AM

03-03-2005, 11:53 AM
:) thanks redrum.... err.... redram

JHawk GT
03-03-2005, 09:04 PM
Was the prestone unopened and sealed? It'll mix ok, but I'd be worried about all the moisture absorbed by the fluid if it was in a container that had already been opened, especially a plastic one. No need to put already contaminated fluid in the brake system when you can buy a fresh pint for a couple of bucks.

03-03-2005, 09:12 PM
yea, dont use opened brake fluid. potentially a bad idea.

09-26-2005, 07:24 AM
it tufff to get the wee little bottles of brake fluid just 500 ml bottles or large . and you don't end up using it all . so it seems a waist to throw out ,what is left in the bottle , after a brake job. wouldn' t the ( plastic bottle the only way it comes )keep it allright. if cap is on dead tight . and to be honest i have used previuosly open bottles for 20 plus years. with no problems i can see. from dot 3 / to dot 4 / to dot 3 specifically for abs brake stystems/ and dot 3 for ford vehicles . all motormaster > canadian tire brand. and with my 86 jeep for many years / each year it is in winter storage i would juist take a turkey baster and sipon out the brake fluid from the master cylinder and refill it, and did not even bleed the lines . now i have new brakes on it as of a few years ago. and now that the last three years it has not been driven or even had the brake fluid changed as describe in this email. so maybe i will find problems . maybe ??? it will get change this month along with coolant too long life orange coolant , the time it was last changed is longer then three years..

09-26-2005, 10:17 AM
Its not that big a deal using a well sealed but opened container...certainly no worse then the 5 year old fluid thats in the brake system now!!! If you are low on fluid, you should check or have checked for leaks. Brake fluid wont go low enough to turn the light on if its not leaking...not even if every pad on the car is shot. (as pads wear, the system uses fluid from the master cylinder to displace the piston. When you replace the pads, the master cylinder fills back up.)

09-26-2005, 01:07 PM
Its not that big a deal using a well sealed but opened container...certainly no worse then the 5 year old fluid thats in the brake system now!!!

LOL 5 years! Brake fluid is one of the most overlooked maintenance items on cars, most people never have it completely flushed and only have a small amount added when changing brake linings.

However, ideally, you should flush your brake fluid every 2-3 years as "wet" brake fluid (brake fluid is hygroscopic and absorbs water) performs far worse than new brake fluid.

DOT 3 and 4 can be mixed though, that's fine. Just stay away from DOT5 as it is silicone and *not* compatible. As an aside, some of the better brake fluids out there are ATE SuperBlue/TYP200 (DOT4) and Motul. Those are harder to get though, and for stuff you can find on a local store shelf I'd look for Valvoline Synpower brake fluid in the silver/platinum coloured bottle--it's DOT4 and has pretty good dry and wet boiling points and lower than normal moisture absorbtion.