I am the second owner of a car. I cannot ID the type of brake fluid currently in the cylinder, however, the car‘s manual specifies DOT 3 or DOT 4 must be loaded. I plan to buy DOT 4, and I plan to add it before the current fluid has completely run out. Assuming the previous owner used DOT 3 or DOT 4, If it happens to be DOT 3 and I add DOT 4, will it be OK?
This Site Might Help You. RE: Can you mix dot 3 and dot 4 brake fluid? I am the second owner of a car. I cannot ID the type of brake fluid currently in the cylinder, however, the car's manual specifies DOT 3 or DOT 4 must be loaded. I plan to buy DOT 4, and I plan to add it before the current fluid has completely run out. Assuming the previous owner used DOT 3.
There is no problem in mixing the DOT3 and 4 fluids together. They do have different specifications, but in normal car operation it will have no affect on brake operation. The most that will happen is that adding DOT 4 fluid to DOT 3 will somewhat equalize the specs in between the two. Now, since brake fluid is designed to absorb small amounts of moisture from the brake lines, it would be a good idea to bleed, or flush, the brake system with good, clean brake fluid every few years. If the brake fluid is dark, then it is contaminated with moisture and other contaminates as is designed to do and should be bled with new, clean fluid until the brake fluid comes out clear from all 4 wheel brakes. I'm also curious as you say you plan to add more before it completely runs out. It should not be running out as it is a sealed system. If you are losing fluid, then you have a leak somewhere, most probably in one of the wheel slave cylinders or the master cylinder, and should be fixed as soon as possible to maintain proper and safe brake operation. Now with that said, brake fluid level will go down normally as the brake pads wear down and will return to its proper level when the brakes are replaced with new ones. So you may wish to check your brakes first before adding more fluid which in the end may not be necessary and may cause an overflow of fluid when the brakes are replaced because they have worn down considerably. It's up to you now. Best of luck.
