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E90/E91/E92/E93 (2006 - 2013)
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  #1  
Old 04-17-2014, 12:04 PM
fullmetalbimmer fullmetalbimmer is offline
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Brake fluid flush

My light came on and it says I need a brake fluid flush, car is a 2008 335I with 25k miles, is this something I should do or just reset the light
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  #2  
Old 04-17-2014, 12:08 PM
wilt wilt is offline
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"Braking systems aren't indestructible. Parts, like the rubber in the valves in the master cylinder, calipers and wheel cylinders deteriorate. All the nasty little bits that flake off end up in your brake fluid. Plus, the fluid itself can get old and worn out. Moisture can also get in the system. That leads to rust, which leads to more nasty bits in your brake fluid. All this adds up to a brake system with compromised effectiveness and decreased stopping power."

Due to the fact that brake fluid picks up water and also other stuff, the recommendation is that your brake fluid be replaced (flushed) every two years. It is 'hygroscopic'...it picks up moisture. As the concentration of moisture increases, it causes a sharp drop in the fluid's boiling temperature. Brand new DOT 3 brake fluid must have a dry (no moisture) boiling point of at least 401 degrees F, and a wet (moisture-saturated) boiling point of no less than 284 degrees. Only one percent water in the fluid can lower the boiling point of a typical DOT 3 fluid to 369 degrees. Two percent water can push the boiling point down to around 320 degrees, and three percent will take it all the way down to 293 degrees, which is getting dangerously close to the minimum DOT and OEM requirements.

DOT 4 fluid, which has a higher minimum boiling temperature requirement (446 degrees F dry and 311 degrees wet) soaks up moisture at a slower rate but suffers an even sharper drop in boiling temperature as moisture accumulates. Three percent water will lower the boiling point as much as 50%!
Water contamination increases the danger of brake failure because vapor pockets can form if the fluid gets too hot. Vapor displaces fluid and is compressible, so when the brakes are applied the pedal may go all the way to the floor without applying the brakes!

In addition to the safety issue, water-laden brake fluid promotes corrosion and pitting in caliper pistons and bores, wheel cylinders, master cylinders, steel brake lines and ABS modulators.

Last edited by wilt; 04-17-2014 at 12:21 PM.
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Old 04-17-2014, 02:39 PM
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Zooks527 Zooks527 is offline
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Quote:
Originally Posted by fullmetalbimmer View Post
My light came on and it says I need a brake fluid flush, car is a 2008 335I with 25k miles, is this something I should do or just reset the light
Do it. Every 2 years for street use, or every track day.
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Old 04-17-2014, 02:47 PM
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bear-avhistory bear-avhistory is online now
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Its on them so do it. Mine is due & will take it in even though its gone on June 5th
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Old 04-17-2014, 03:45 PM
santostefano santostefano is offline
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Wilt did a very nice job of explaining the situation with brake fluid. Too many people never think about changing brake fluid, especially in domestic cars. Mine is a 2008 3351 convertible with 6000 miles that I have owned since September of 2013 (great find due to an estate sale). The light came on indicating that the brake fluid needed to be changed. It had been changed a little over two years ago. I found the procedure for resetting the indicator and did it. I plan on changing the fluid some time late this year. Do you know the reset procedure for the indicator light?...ds
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Old 04-17-2014, 05:12 PM
ericgl ericgl is offline
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Last week I bought an 08 e92 335i with 13,500 miles. Before I got it home the red service light came on. Brake fluid and engine oil. I've reset the interval, but I am taking it in tomorrow. I will also change the coolant.
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Old 04-18-2014, 12:03 AM
sptt144 sptt144 is offline
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I had a '91 Mercedes with over 200K miles. Never had brake fluid done. Put new rotors and brakes (textar) on and damn thing stopped on a dime whenever I needed it. I have never replaced brake lines or brake fluid in any of my 10 cars or trucks in 32 years. Never had a braking problem besides normal worn brakes. Systems seem to hold up very well no matter what I've had. No accidents either to this date. I just do every day driving. If I can't stop, with good brakes, then I will look at fluid and lines but have never had to. How often do Boeing and Airbus bleed their lines? Just curious...they had better be sure they can stop!

Last edited by sptt144; 04-18-2014 at 12:04 AM.
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Old 04-18-2014, 10:13 AM
badbrad10 badbrad10 is offline
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same here new brake fluid flush

I 40. yrs of driving, 15 or so vehicles from domestic, audi, acura, high performance Camaros & mustangs, I drove police vehicles on highway patrol for 25 yrs including 440 mopars, LT1 Caprices, ford crowns, lots of hot hard braking pursuits and emergency driving, I never ever had brake fluid flushed in my pvt or govt cars. I don't plan on doing it on my 335iX E92
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Old 04-18-2014, 11:35 AM
Ml3456 Ml3456 is offline
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I think its the abs equipment that is more effected. Used to not change fluid also. Never seemed a problem. Bought a 4 year old Pontiac Bonneville in 2004 with 11.000 miles. Extremely clean. But the brake fluid was green. Changed the fluid after I got it, but wasn't much longer and needd to replace the abs pump!!
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Old 04-18-2014, 11:54 AM
haskindm haskindm is offline
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The importance of flushing brakes came to light after the advent of ABS Systems. The pump is very sensitive to moisture in the fluid. If the pump corrodes it can be VERY expensive to repair. New systems require rethinking the old maintenance.
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Old 04-18-2014, 11:58 AM
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cwinter cwinter is offline
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Since you can't tell visually what state brake fluid is in, I change it every 2 years. I think the dealer charges about $80 for it, which is pretty cheap maintenance/insurance every 2 years.
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