Your propane is delivered and stored in liquid form. Propane liquid, for example, will expand (become a gas) nearly 17 times more than water over the same temperature increase. As a result, tanks and cylinders are never completely filled with propane liquid. Tanks are filled to about 80 to 85 percent of their capacity. This leaves a space above the liquid, which allows the propane liquid to expand freely due to changes in temperature.
Heat is added to or taken from propane stored in a tank or cylinder by transfer directly to or from the air surrounding the container. Hot days, cool nights, rain and snow are a few of the many factors that affect the temperature of the liquid. Because of these ambient temperature changes, you may see fluctuations in your container gauge.