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The brake light is on in my 2007 Toyota Tacoma 4WD v6. The recurring pattern has been that I would fill up the brake fluid but then it would drop below the minimum mark after just a few days. It doesn't go below though. The brakes function fine. I have no clue why this happens.

I just went to AutoZone to get more brake fluid and picked up DOT 3 from the shelf because that's what I had been getting. I asked the associate just to confirm that's the right kind for my truck and she checked in the computer and said I needed 'DOT 3/4'.

Q1. Was she correct?

Q2. If A1 is yes, could my brake problems be coming from the wrong kind of brake fluid?

Q3. Can I replenish the existing DOT 3 with DOT 3/4, i.e. is it bad if they mix?

Q4. Do I need to bleed out the whole system?

RELATED: Brake fluid reservoir level drops fast to minimum but not below

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What year and does it have ABS ? – mikes Dec 30 '13 at 1:52
2007 TRD package, dunno about ABS – amphibient Dec 30 '13 at 4:35

Prestone does make product that is compatible with DOT3 and DOT4 fluid referred to as DOT3/4. Several sites state you can use 4 in place of 3. However using 3 in place 4 may decrease brake performance. Without knowing the year it is hard to tell which is the most correct type of fluid for your Toyota. Regardless of the type used, that is the lesser of your problems. Brake fluid is not normally a consumable item. It should not have to be added as part of routine service. If you must add it on a regular basis you have a leak. If it never goes below the minimum mark it may be the reservoir that is leaking. If the leak is not repaired you may get to the point that the brakes fail.

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Here is a great article on brake fluids and such. – Pᴀᴜʟsᴛᴇʀ2 Dec 30 '13 at 3:36

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