If you prop up the rear end of the truck higher than the front, you can loosen the temperature sensor in the back/top of the head to let air out and you fill it back up. You might need the engine to be running to get the air to all circulate to that spot so be careful and have someone at the wheel ready to turn off the truck should you accidentally unscrew the sensor too much and it pops off, spraying you with coolant. Safety glasses are a must and it's even better if you have a rag over the sensor as you're working to keep the spray to a minimum.