Abstract: A filtering device (15) for use in a cooling system for motors or engines such as for example vehicle or boat engines or alternatively stationary engines having a cooling circuit around which the coolant passes. The device includes a bag-like member (16) which is comprised at least in part by mesh material, the bag-like member, in use, being disposed within the coolant circuit, so that the coolant passes through the mesh material and the bag-like member collects deposits carried by the coolant therein. A magnet (17) may also be provided within the bag-like member. Furthermore, the bag may be stretchable so that the mesh can expand under pressure.