Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

Brake Fluid discussion

I recently had a mechanic replace the brakes on our Toyota Venza. I asked if they were going to replace the brake fluid - mechanic said no, just top it off. In the past when I did a brake job, I always drained the brake fluid and replaced it. I thought this helped preserver the brake lines, master cylinder, etc. Is there something new with brake systems now; was I wrong with my past practices?

Yes, brake systems have changed. They contain different metals that react to one another when old, damp brake fluid is in the system!

I commend your practice of replacing brake fluid. Find a new mechanic or insist he change the fluid. It prevents corrosion in your brake system and raises the fluid boiling point considerably.

Did they at least test the brake fluid for copper content.

These test strips detect the amount of copper dissolved in the brake fluid to indicate when the brake fluid should be changed.


Do those test strips detect moisture in the fluid? Particulate debris gathered in the calipers?
Whenever I’ve changed the fluid in a car that hasn’t had it in a long time there’s nasty looking muck that comes out when I first open the bleeders.
Always seems to look worse than what was in the reservoir.
I change the fluid on my non-ABS car every 3 years. With ABS I’d do it every 2 years.

I usually replace the brake fluid in the portion of the brake system I’ve been working on. I have to bleed it anyway, so replacing it isn’t that much more difficult. I guess a person could argue the less you do, the less chance you’ll get contamination into the fluid. There’s some merit to that argument I think. I don’t replace the brake fluid for no reason for example. Only if I’ve done some work on the system so I had to open the hydraulic lines anyway.

If there’s dissolved copper in the brake fluid, it means there’s enough moisture in the brake fluid to cause the copper to oxidize.


whenever I change pads or shoes I flush all my lines

the old brake fluid is always very dirty, dis-colored, when I do.