With the car on level ground and the engine off, find the brake fluid reservoir, usually near the back of the engine bay on the driver's side. The level should sit between the MIN and MAX marks. Fresh fluid is usually clear to amber, while dark fluid may need changing. A falling level can mean worn pads or a leak.

Brake fluid absorbs moisture over time, which lowers its boiling point. Many car makers recommend changing it about every two years, but follow the service schedule for your vehicle.

Changing brake fluid means bleeding the old fluid out of each wheel while topping up the reservoir with new fluid, usually starting at the wheel furthest from the master cylinder. Some vehicles with ABS need a specific procedure. If you haven't bled brakes before, it's worth having it done professionally.

In many cars, yes. Hydraulic clutches often use the same brake fluid, and some share the brake reservoir. Always check the cap or your owner's manual for the correct fluid type.

DOT 3, DOT 4 and DOT 5.1 are glycol based and are generally compatible. DOT 5 is silicone based and must never be mixed with them. The safest choice is the fluid type your vehicle's manufacturer specifies.