Topping-up the Radiator

The water level in the radiator header lank should be checked regularly, although frequent topping-up should not be necessary. The filler cap is fitted with a spring-loaded valve that maintains a modest pressure in the system when the engine is hot, thus raising the boiling point and also preventing loss of water. Owing to the pressure

The pressure-retaining radiator filler cap: 1, overflow; 2, sealing washer on spring-loaded valve




 
 
existing in the system when the water is hot, the cap should be wrapped in a cloth before it is removed and to avoid any risk of scalding it should be turned progressively to allow the pressure to escape before it is finally lifted off.

It is bad practice to top-up the system when the engine is cold. This is likely to lead to unnecessary loss of water (and relatively expensive anti-freeze solution, when this is in use) as the water in the system expands when the engine warms up.

When anti-freeze is in use (see below) it is always better to top-up with a solution rather than pure water. The anti-freeze ingredient in the solution itself does not evaporate, but when fairly frequent topping-up is needed it is obvious that the coolant must be escaping through a Teak at some point, It is necessary to discover and cure the leak and then add anti-freeze solution to prevent the remaining solution being unduly weakened.