Brake Fluid Tester
Brake fluid testers offer a cheap, compact, and easy way to get an indication of the state of brake fluid, without removing brake fluid from the vehicle.
Brake fluid is a mixture of synthetic organic chemicals which transmits hydraulic pressure from the brake pedal through hydraulic lines to the braking mechanism. To make this possible, brake fluid must be incompressible.
Braking generates considerable heat so, to resist these high temperatures without boiling, brake fluid is designed with a high boiling point. However, brake fluid is hygroscopic, which means it absorbs water, normally from the air through the flexible brake hoses or the reservoir breather. This moisture reduces the brake fluid’s boiling point.
Once this moisture absorption reaches a certain level the generated heat can cause the brake fluid to boil, creating gas bubbles. As gas is far more compressible than liquid, the driver will experience a lack of pressure on the brake pedal (a spongy pedal), resulting in a loss of brake power. This is known as ‘vapour lock’.
The brake fluid chosen to put into the hydraulic system is critical, with vehicle manufacturers recommending a specific type of fluid that should always be adhered to.
Although many vehicle and brake manufacturers give minimum recommendations, the right time to change the brake fluid shouldn’t be based on the vehicle’s mileage or age.
Conductivity or “pen type” testers estimate the water content electronically. In theory, conductivity (and/or capacitance) increases with moisture content. Although they’re not foolproof, these testers offer a cheap, compact, and easy way to get an indication of the state of brake fluid, without removing brake fluid from the vehicle.
- Colour coded LEDs show level of water:
- Green: Battery OK - No water found
- Yellow: Less than 1% water - No action necessary
- Yellow/Yellow: 2% Water found - Check regularly
- Yellow/Yellow/Red: 3% Water found - Change brake fluid
- Yellow/Yellow/Red/Red: 4% Water found - brake fluid should be changed immediately
- CE & UKCA compliant