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Importance of replacing brake fluids

Hello, I am not an expert in auto related stuffs, but I heard that replacing the brake fluid is an important part in auto maintenance. I saw a blog ( http://www.serviceplus416.com/car-news/why-its-important-to-replace-your-brake-fluid/ ) which talks about the same. I realized the importance of replacing brake fluids and how it becomes an important part of routine maintenance. But, I have a question now, if brake fluid is contaminated, should I need to be concerned?

“If brake fluid is contaminated, should I need to be concerned?”

You should be concerned to the point where you flush out all of the old brake fluid and make sure you replace your brake fluid at the proper interval in the future. I have never flushed any brake fluid that looks as good going out as it did when it was going in.

If you’ve detected contamination in your brake fluid you should be concerned. You should flush the system with fresh fluid.

Brake fluid absorbs moisture and that in turn will contribute to metal brake lines rusting. I’ve seen it happen a couple of times, dangerous!

Honda was on the ‘flush the brake fluid’ bandwagon from the '76 Civic-I don’t know about the AN600. Moisture contaminated brake fluid in steel parts = rust, which damages rubber seals and brake lines from the inside out.

My attitude is: flush the fluid when you service the brakes. Good practice is to bleed the brakes when you change pads–it isn’t that much more work to continue bleeding until you push fresh fluid out the bleeders.


I don’t have a fluid-changing regemin beyond that, however.

I got in the habit of changing brake fluid in my '81 Accord.
Do it every 3 years now. If I had a car with ABS I’d do it every 2 years.
Old fluid always looks dark. That’s enough evidence for me.

I am in CA where moisture is not much of an issue (we are going through a long drought), but after 18 months my fluid is dark, so I usually change it at 2 yr intervals. If I am doing a brake job, I change the fluid too b/c as mentioned above it is not that much work and I also have to buy a bottle of fluid and hate to waste it.

I’m with @meanjoe75fan on this. I only change it out when I have to do someone that involves opening the brake lines anyway. My thinking is if I mess around with it, I may do more harm than good. It is very easy to contaminate brake fluid, and even miniscule dirt particles will clog up the passages. And then I only change it on the brake circuit I’m working on. Usually I have to do something with the brakes on the Corolla every 2-3 years, change the front pads or the rear shoes, etc, so one of the circuits is getting new fluid at about that interval. Has worked ok for me. Never had to replace a brake master cylinder, disc brake caliper, drum wheel cylinder, or metal brake line in over 20 years. Mild Calif climate probably contributes.

Well, you are messing with it when you are doing the pads and then flush the fluid, so how is that better than a simple flush every 2 years even if you don’t need pads. I say this because on the car that I drive the miles are mostly fwy and I am very good in adjusting my speed, so I can easily go 100K miles with no need for new pads; my wife’s car is a different story.

Every 3 years on my street cars because of moisture and corrosion. Every 6 months on the car I take to track days because of moisture.

Any moisture at all lowers the brake fluid’s boiling temperature. When you are hard into the ABS doing 120 mph at the end of the longest straight-away staring at a 90 degree turn needing 55 mph to make, you don’t want the fluid to boil! Extreme? Yes. Keep that in mind the next time you are driving down a long hill in the the Rockies or Appalachian mountains.

I seem to recall, in Germany your car fails if the brake fluid is too old. That is during the safety inspection

I can’t remember if they actually tested the boiling point, or if they fail you if the fluid’s black as tar

Do any of the state inspections here address the brake fluid in any way?

In Colorado I don’t think they looked at the brake fluid other than maybe check the level. For brakes, they did require one of the front wheels be pulled and the drum removed to measure the thickness remaining on the brake linings. Not a big job for a normal car, but somewhat more timing consuming for 4WD vehicles. I don’t think they were allowed to charge more for 4WD cars, so they were always looking sad when I pulled in w/my 4WD truck for an inspection … lol …

For some reason here in Northern California at least no safety inspection is required. Emissions testing yes. For safety you are on your own.

No safety inspections in southern California, either

And the cars show it . . .

Heat is also a factor in brake fluid degeneration as @Mustangman‌ alluded to. If you use the brakes frequently while you drive, like with constant hard braking on the highway, that ruins the fluid too.

I just ordered one of these for Dot 4 fluid

For $22, this is a cheap tester every inspection station or mechanic should have. They are available for Dot 3, too.

This article says that Dot 4 fluid should be changed more frequently than Dot 3:

http://stoptech.com/technical-support/technical-white-papers/brake-fluid

Pull quote:

A seldom talked about characteristic is that because of this chemistry, the DOT 4 fluid will have a more stable and higher boiling point during the early portion of its life, but ironically once the fluid does actually begin to absorb water its boiling point will typically fall off more rapidly than a typical DOT 3.

This is the first I’ve ever heard of this.

@insightful; Thanks for posting that. Maybe that is why mine gets dark fast. Not that the color is the best indicator, but still bothers me. The tool posted by Mustangman is neat too, not sure if I can skip changing the dark fluid after 2 years even if it check okay. Seems a bit like sending your oil to blackstone for testing.

If you try to open a 3 year old bleeder around here there is a very strong likelihood of breaking it off.

If I lived in the rust belt I’d put a dab of grease around the outside of the bleeders each fall (along with other rust preventive measures).