Improving network lifetime is an important issue involved in every aspect of the design and deployment of wireless sensor networks. There is a recent research trend of studying the application of a mobile sink to transport (rather than let the sensor nodes transmit) data back. Whereas this approach trades data delivery latency for reduced (node) energy consumption (and thus an improved lifetime), our experience tells us that sacrificing latency to extend lifetime is not necessary. In this paper, in line with our previous work, we investigate the approach that makes use of a mobile sink for balancing the traffic load and in turn improving network lifetime. We engineer a routing protocol that effectively supports sink mobility. Through intensive simulations in TOSSIM with a real implementation, we prove the feasibility of our mobile sink approach by demonstrating the improved network lifetime in several deployment scenarios.