Test your brake fluid
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A DEVICE to chec the moisture level in hydraulic brake fluid has been introduced by Castrol.
The Vapour Lock Indicator, which is intended for use by the garage or fleet operator, can establish the temperature at which the brake fluid ceases to be effective.
At this temperature, called the "vapour lock point", the fluid starts to vaporise resulting in a spongy pedal or even total, if temporary, loss of braking.
When the fluid cools, normal braking is restored.
When new, a good quality brake fluid has a vapour lock point of around 240°C (464°F) — more than twice the boiling point of water.
In service, however, it absorbs moisture from the atmosphere and this can progressively reduce the vapour lock point to below the potentially dangerous level of 155°C (311°F).
Castrol claims that the Vapour Lock Indicator makes it possible for the vapour lock point of hydraulic fluid to be checked periodic ally after taking a small sample of the brake fluid from the bleed nipple at the left-hand front wheel. Sampling from the wheel, rather than from the more accessible master cylinders, is essential because the vapour lock point of the fluid in the wheel area is almost invariably lower than at the master cylinder.