Engine oil can be over cooled during short journeys, light loads or cold winter conditions a thermostat controlling flow through the oil cooler avoids this. This extra cost option can be specified at a modest price when ordering - a wax stat thermostat valve similar to the principal used in the engine water thermostat is housed in a specially cast and machined cavity in the supply return 'sandwich plate' adaptor.
Oil cooling is universally adopted to protect the engines of competition cars, used for road rallies and race track events, as well as classic cars trying to cope with the extra heat of lower octane fuels and the stress of keeping up with modern motorway traffic! In fact any vehicle that has to work harder than normal.