We examine the performance of the TCP protocol for bulk-data transfers in mobile ad hoc networks (MANETs). We vary the number of TCP connections and compare the performances of three recently proposed on-demand (AODV and DSR) and adaptive proactive (ADV) routing algorithms. It has been shown in the literature that the congestion control mechanism of TCP reacts adversely to packet losses due to temporarily broken routes in wireless networks. So, we prospose a simple heuristic, called fixed RTO, to distinguish between route loss and network congestion and thereby improve the performance of the routing algorithms. Using the ns-2 simulator, we evaluate the performances of the three routing algorithms with the standard TCP Reno protocol and Reno with fixed RTO. Our results indicate that the proactive ADV algorithm performs well under a variety of conditions and that the fixed RTO technique improves the performances of the two on-demand algorithms significantly