The flow of the coolant is generated by the Nissan water pump on the front of your engine. This is a very durable mechanical part, and the only weakness is the seal on the impeller shaft which will wear out in time. The Nissan water pump receives the coolant from the radiator through the lower coolant hose. The coolant is then pumped into the engine block so a constant temperature can be maintained in the engine. As with all polymer seals, the one on the impeller shaft will wear out eventually, coolant will begin to leak from it. Since the water pump is directly connected to the Nissan engine block, it is hard to see it and the leak by looking at the engine from above. It may also be covered by the fan pulley that is connected to the end of the impeller shaft. The best manner in which to view the small hole in the bottom of the water pump where the leaking coolant will exit this device from is by looking up from under the engine. This is most easily accomplished when your Nissan is suspended up in the air on a lift. The most difficult part of the water pump replacement procedure is actually getting to the pump itself. The radiator fan shrouds and other devices on the front of your Nissan engine will have to be removed first before access to the pump will be possible. Once this is accomplished, the surface on the engine block where the water pump is placed and seals the coolant in this closed loop system have to be cleaned of any old gasket material along with coolant and oil. This will make it possible for the new seal to be proper and hold the coolant in place when the engine is operating.