When adding fluid to the system ONLY use fresh DOT 3 brake fluid from a sealed container. DOT 3 brake fluid will absorb moisture when it is exposed to the atmosphere, which will lower its boiling point. A container that has been opened once, closed and placed on a shelf will allow enough moisture to enter, over time, to contaminate the fluid within. If your brake fluid is contaminated with water, you could boil the brake fluid under hard braking and loose all/some of the brake system. Don't take the risk, buy fresh brake fluid whenever you must add to the system.
See Figure 1, 2 and 3
Brake fluid level and condition is a safety related item and it should be checked ANY TIME the hood is opened. Your vehicle should not use brake fluid rapidly (unless there is a leak in the system), but the level should drop slowly in relation to brake pad wear.
The master cylinder reservoir is located under the hood, on the left side firewall. All vehicles covered by this guide should be equipped with a see-through plastic reservoir. This makes checking the level easy and helps reduce the risk of fluid contamination (since you don't have to expose the fluid by opening the cap to check the level). Fluid should be kept between the MIN and MAX lines. If the brake fluid level is near or below the MIN mark, fill the reservoir to the MAX mark.
If it becomes necessary to add fluid to the system, take a moment to clean the area around the cap and reservoir. Use a clean rag to wipe away dust and dirt which could enter the reservoir after the cover is removed. If the level of the brake fluid is less than half the volume of the reservoir (and the brake pads are not approaching a replacement point), it is advised that you check the brake system for leaks. Leaks in the hydraulic system often occur at the wheel cylinders.