In any engine cooling system, de-aeration capability of the system plays a very critical role to avoid over heating of an engine. In general, with recovery bottle engine cooling system there is one vent hose from radiator pressure cap to the recovery bottle and coolant in the bottle is exposed to atmospheric pressure. From this vent hose air bubbles will move to recovery bottle from the engine and radiator when pressure in the system exceeds pressure cap setting. With this arrangement, de-aeration from the engine will happen when thermostat opens only and till that time air bubbles will be in the engine only and in this time there will be chance of overheating at some critical conditions because of air pockets in to the engine water jacket and the entrained air in the cooling circuit. Also, secondly 100 % initial filling cannot be achieved. Thus there is a need for continuous de-aeration irrespective of the thermostat opening/closing position and also to reduce number of filling intervals.This paper reports on improvement of de-aeration by adding a secondary de-aeration circuit for an engine cooling system with recovery bottle for a single cylinder light commercial vehicle. The secondary de-aeration circuit enabled continuous de-aeration for the cooling system with recovery bottle which performs with similar principle of cooling system with degas bottle and also reduced the number of filling intervals during the de-aeration test. This arrangement can be done to get weight and cost benefits over degassing tank, wherever it is technically possible (i.e. Radiator coolant inlet port should be higher than the engine coolant outlet port). The secondary vent added between top most point of the engine before thermostat valve to the radiator filler neck. A study was carried out on a vehicle with and without a secondary vent in the cooling system with respect to De-aeration, Initial filling capacity and Filling time. The test results confirmed significant improvement of de-aeration and initial filling capacity by adding secondary de-aeration circuit for an engine cooling system with recovery bottle.