Help - Brake Fluid Question

"tuxOnWindows" (tuxonwindows) 01/02/2018 at 15:31 • Filed to: None

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I need to top up the brake fluid on my 2011 Subaru Legacy GT but I’m unsure what type to use. The manual states to use either DOT 3 or DOT 4 & there’s a warning underneath that states “Do Not Mix DOT 3 & DOT 4 brake fluids”.

I have no clue what type is already in it, is there any sort of test I could do at home to determine it?

Dogapult > tuxOnWindows 01/02/2018 at 15:40

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Pretty damn sure you can mix DOT3 and DOT4. Just not DOT5.

dogisbadob > tuxOnWindows 01/02/2018 at 15:42

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You can mix DOT 3 and DOT 4 with no problems :)

And you don’t top off brake fluid. When it’s low, it usually means your pads/shoes are worn, but in some cases it can indicate a leak.

The solution is to replace your pads and rotors. I recommend coated rotors like Wagner E-shield or Centric Premium, which have a coating to help stop rust. Akebono pads are good too.

If you wish to flush your brake fluid, use any DOT 3 or 4. In fact, some brands such as Valvoline even say DOT 3/4 on the bottle. You should flush it whenever you replace the pads and rotors since you’re already in there anyway. And speed bleeders are awesome.

Regular brake fluid changes are MUCH more important than what brand you use.

Just DO NOT USE DOT 5! It is silicone shit that will turn your brake lines into goo since it DOES NOT mix with DOT 3/4/5.1

BeaterGT > tuxOnWindows 01/02/2018 at 15:45

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Flush and Replace with DOT 4! By the way, awesome car. Makes me want to upgrade from my 2005.

tuxOnWindows > dogisbadob 01/02/2018 at 15:49

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Thanks, I’ll try the Valvoline DOT 3/4. It’s probably due to the negative temps & pad wear. I just want to add enough to keep my ebrake light from sticking on or randomly coming/going while driving.

jimz > tuxOnWindows 01/02/2018 at 15:50

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the warning is probably just a CYA; DOT 3 and 4 are both glycol-ether-based fluids. IIRC DOT 4 has a higher boiling point.

DOT 5 is silicone-based, and you do not mix it with 3 or 4.

KusabiSensei - Captain of the Toronto Maple Leafs > tuxOnWindows 01/02/2018 at 15:56

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Do you have an explanation from someone as to why your brake fluid is low? Brake fluid isn’t consumed (it’s just a force transfer medium), so if it gets low that means you either need new brake pads (or a parking brake shoe) or you have a leak, which is very very serious.

crowmolly > tuxOnWindows 01/02/2018 at 16:06

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Should say right on the cap what’s in it. Top it off, but make plans to do the brake job it probably needs in the near future.

tuxOnWindows > KusabiSensei - Captain of the Toronto Maple Leafs 01/02/2018 at 16:08

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My parking brake was repaired last October due to being stuck & the ebrake light issue appeared 3-5 weeks afterwards when it started getting colder. I had my timing belt replaced in December & mentioned this issue to the shop, but they were unable to replicate it & did not find any leaks.

dogisbadob > tuxOnWindows 01/02/2018 at 16:25

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if it’s low enough to trigger the brake light, you definitely need new brakes. Order them on Amazon, eBay, Rock Auto, or your favorite parts store site today (or go to your favorite local parts store this week) and change them over the weekend.

Simply being cold, even negative temps, does NOT make it low enough to trigger the brake warning light without the pads being severely worn. The expansion/contraction rate is not THAT much!

Ash78, voting early and often > tuxOnWindows 01/02/2018 at 16:39

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FWIW, Dot 3 is usually easier to find in large bottles at 1/3 the price (per ounce) of Dot 4. The latter is probably overkill for most usage. Maybe if you’re autocrossing on Venus and not letting the brakes cool down between runs...

KusabiSensei - Captain of the Toronto Maple Leafs > tuxOnWindows 01/02/2018 at 19:28

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As has been mentioned by dogisbadob, you likely need new brake linings. Especially if the light came on after multiple weeks following the repair.

If you replace the linings, you’ll probably find that the fluid level returns to normal without topping it off.

Khalbali > tuxOnWindows 01/02/2018 at 20:58

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My light is on constantly because I was too lazy to do my brakes before winter and now it’s too cold so I’m waiting till spring. But NC miatas have a notoriously low threshold for the light coming on, first time it came on under hard acceleration and there was still 50%+ pad left.