Methods and apparatus to cool a vehicle heat source are disclosed herein. An example apparatus includes a first tank and a second tank. The first tank and the second tank are disposed on a vehicle. The second tank is in fluid communication with the first tank. An engine of the vehicle is to be supplied with fuel from at least one of the first tank or the second tank. The example apparatus also includes a cooling system disposed on the vehicle to cool the fuel flowing from the first tank to the second tank. The example apparatus further includes a heat exchanger operatively coupled to a heat source disposed on the vehicle. The fuel from the second tank is to flow to the first tank via the heat exchanger to cool the heat source.