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Old 08-20-2009, 01:42 AM   #1
only1agam
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Default Synthetic brake fluid=cheaper maintenance

so i realize that the manual says the brake fluid in the wrxs needs to be changed every 30,000 miles. i don't autocross or anything, just use the car for normal driving. If I were to swap to a dot 4 synthetic brake fluid, (vs. the oem fluid), can I go without draining the brake fluid every 30k without damaging anything? thanks!

(the goal here is to do less maintenance. i was thinking synthetics hold up better so why not use that and change less than using 30k miles for the next BF change.)
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Old 08-20-2009, 02:05 AM   #2
Andrew2.5
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well i know first of all alot of people dont even bother changing it at 30k if at all other than a major brake swap...
Now about the fluid... Dont quote me on this but i really dont thing syn fluid will extend your service intervals. Blake fluid is hydroscopic which from what i understand means it absorbs moisture in the air...
With that said i would think that synthetic would preform better but still absorb moisture as non synthetic does... Thats the reason subaru recommends it be changed...
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Old 08-20-2009, 10:14 AM   #3
drivin blind
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Someone will surely correct me if I'm wrong, but I don't think Dot 4 is synthetic and can be used the same as Dot 3. Just a higher boiling point. RP
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Old 08-20-2009, 10:22 AM   #4
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Brake fluids unlike oils aren't really divided into 'synthethic' and 'dino'

They are all 'synthetic' glycol-based fluids with the exception of DOT5 which is also synthetic but silicone-based - so if you see 'synthetic' on a bottle of brake fluid it is really just hype.

The reason for changing brake fluid regularly is that it is hygroscopic (absorbs water). A DOT4 fluid should start with higher wet and dry boiling points and degrade slower than DOT3 - but higher 'performance' (which usually means higher dry boiling point) fluids such as the DOT5.1 'race' fluids may in fact absorb water more quickly i.e. need to be changed MORE often.

For the record you should NOT use the silicone-based DOT5.
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Old 08-20-2009, 12:10 PM   #5
only1agam
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so if i were to put in some motul rbf600, would i have to keep up with the same 30k mile maintenance interval?
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Old 08-20-2009, 01:38 PM   #6
09rexwagon
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This is a sickening fact: 75% of cars on the road with over 100k miles have the original brake fluid in it.

That probably means there is a relatively high %age of water in it so when they try to brake in an emergency situation, the water pockets boil, and the vapor bubble collapses and the pedal flies to the floor and they hit the person in front of them.

The sad thing is that most car manufacturers only recently started adding brake fluid to the recommended maintenance. 10 years ago, you'd never see brake fluid mentioned in the manual. I personally think that the % water should be tested as part of yearly inspection and have it be a fine-able offense or a registration block if it is too much.

I always bleed my brakes and clutch with new fluid every 2-3 years. New fluid can take in up to 1% H20 in 1 year...even with a well sealed system.
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Old 08-20-2009, 09:51 PM   #7
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Quote:
Originally Posted by only1agam View Post
so if i were to put in some motul rbf600, would i have to keep up with the same 30k mile maintenance interval?
the high performance brake fluids are generally much more hygroscopic, so you'd need to change the fluid more frequently or risk corrosion (the boiling point is still pretty high for dot 5.1 fluids when wet, so it won't boil, but they still become very corrosive when the water level gets high)

Unless you track the car, there's really no reason to go beyond a dot 4 - you'll never use the extra performance (i.e., increased boiling point) you pay for with the dot 5.1

funny thing here is I change my fluid generally once every other year or so, but it hardly even darkens in color (hard to tell when the old fluid has been bled out)... the benefits of living where it hardly ever rains, I guess...
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Old 08-21-2009, 01:33 AM   #8
only1agam
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so if i were to put a dot 4 "synthetic" brake fluid in the car, it would still need to be changed out every 30k miles? i would ideally like to reduce the amount of maintenance on the car rather than change it out every 30k
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Old 08-21-2009, 08:08 AM   #9
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Quote:
Originally Posted by only1agam View Post
so if i were to put in some motul rbf600, would i have to keep up with the same 30k mile maintenance interval?
I wouldnt

many hi performance brake fluids are ment to be changed regularly and not left in the system for a long time

for a dd/street car, a brake fluid with a high WET boiling point is better than one with a high DRY bp

for a race car that gets the fluid changed often, the opposite is true
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Old 08-21-2009, 08:09 AM   #10
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Quote:
Originally Posted by only1agam View Post
so if i were to put a dot 4 "synthetic" brake fluid in the car, it would still need to be changed out every 30k miles? i would ideally like to reduce the amount of maintenance on the car rather than change it out every 30k
d00000000000d

buy a bus pass if you are worried about brake fluid
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Old 08-21-2009, 03:30 PM   #11
DrD
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Quote:
Originally Posted by only1agam View Post
so if i were to put a dot 4 "synthetic" brake fluid in the car, it would still need to be changed out every 30k miles? i would ideally like to reduce the amount of maintenance on the car rather than change it out every 30k
DOT 4 should go the normal length of time, which really should vary with where you are - when the fluid in the res. starts getting dark, change it out (the color change coincides with water uptake)

All brake fluid is synthetic. (even the ones which don't market themselves as "synthetic")
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