Brake fluid flush

[crazyjim]

Marcia had her SUV in for an oil change at the Nissan dealer and they said it was time to flush her brake fluid.  She called me and told her not to do it.  I've never heard of flushing brake fluid.  It's a sealed system isn't it?  Water & air shouldn't be getting in the lines.

Some of you guys a real gear heads and I'd like to hear your opinion on brake fluid flushing.

[Ace-Garageguy]

It's usually unnecessary, and is almost always simply a scare-tactic to pump up the service bill.

Old brake fluids DID in fact absorb moisture over time at a much higher rate than today's fluids do, and it was actually a pretty good idea to change it periodically.

But if it's a newer vehicle, less than 15-20 years old, I'd not even consider doing it.

[Rodent]

What does the owner's manual say? I just looked at a maintenance schedule for a Pathfinder and it recommends changing the fluid every 20,000 miles.

[DonW]

What does the owner's manual say? I just looked at a maintenance schedule for a Pathfinder and it recommends changing the fluid every 20,000 miles.

Well they're in the trade as well! They may recommend which brand of fluid to waste your money on too. Although it may make sense if you only do 1000 miles a year.

Edited February 1, 2017 by DonW

[Ace-Garageguy]

Change your timing belt at specified intervals. It's absolutely critical.

Anything else, not so much.

Edited February 2, 2017 by Ace-Garageguy

[mikemodeler]

As someone who has spent better than 30 years in the automotive biz (parts, service, aftermarket sales, manufacturing) there are several schools of thought on the subject.

1. Depending on how the vehicle is driven and the climate in which it operates, flushing the brake fluid is a good idea. Higher humidity and infrequent vehicle use can contribute to the demise of the fluid.

2. It is a service that ALL vehicle manufacturers and MANY shops will DEFINITELY tell you is necessary for proper operation of your vehicle, but reality it is a service that doesn't always need to be done. If major work is done to a brake system ( caliper replacement, wheel cylinder replacement or master cylinder replacement), most of the brake fluid will be replaced anyway. 

3. Modern brake fluid (Dot 4 and higher) is more resistant to moisture and if the system is kept sealed, flushing isn't necessary.

 

At the end of the day, it comes down to your personal decision and how you want to spend your money. I have never flushed the brake fluid in any of my vehicles and have put over 100,000 miles on several of them and haven't had a problem. 

Oil changes with quality oil and transmission flushes are more important to longevity in modern cars. 

[Tom Geiger]

Be sure to change the air in your tires too!   

[mikemodeler]

Be sure to change the air in your tires too!   

As funny as that sounds, replacing air with nitrogen does have an impact on your tires. Unfortunately, most of the dealers do that to new cars and add $100 to the window sticker!

 

[Ace-Garageguy]

I've been on the dirty end of vehicle maintenance for over 40 years...plus design, restoration, racing, fleet-management, etc.

Brake hydraulic systems in old vehicles frequently had a breather pinhole in the master-cylinder cap that could conceivably allow ingress of moisture.

Modern vehicles almost invariably have a bellows-arrangement that effectively seals the entire system.

That, coupled with the "low moisture activity" of modern fluids makes fluid-changing entirely unnecessary...unless you want to literally keep your car forever (change it maybe every 5-10 years if it makes you feel better), or race it, or if it's sat unused for a long, long time.

I have vehicles with over 200,000 miles on them still happily running their original brake fluid.

10-15.000 mile engine-oil-changes if you're using a quality synthetic should really be perfectly adequate...but be sure to check the LEVEL frequently.

For later model vehicles, follow the book recommendations for auto-trans fluid changes. Though the bulletproof Turbo 350 and 400 GM boxes, C4 and C6 Ford boxes, and Chrysler TorqueFlites could run just about forever on the original fluid, today's cars with more and more internal complication to provide more "gears" for increased fuel efficiency have placed VASTLY higher loads on the necessarily SMALLER internal components.

Edited February 2, 2017 by Ace-Garageguy

[crazyjim]

Thanks for the comments.  I think I did right by saying no.