Complex sentence: The refueling process was delayed due to a vapor lock in the fuel tanker truck's pumping mechanism, and Cooper became suspicious; but he allowed a replacement tanker truck to continue the refueling--and a third after the second ran dry.
Split into simpler sentences: The refueling process was delayed, reportedly due to a vapor lock in the fuel tanker truck's pumping mechanism, and Cooper became suspicious. However, he allowed a replacement tanker truck to continue the refueling--and a third one after that when the second ran dry.