Have you ever run out of propane while you were grilling? So you had to stop halfway through and go buy a fresh tank?Well, some grills have gauges on them that tell you how much is left. But if yours doesn’t, there’s still an easy way to figure it out before you start cooking.Just take a glass of hot water, and pour it down one side of the tank. Then feel it with your hand.The top of the tank should feel warm from the water. But unless it’s completely empty, it should feel a lot colder as you move your hand down. And here’s why . . .Propane absorbs heat faster than air does. And when your tank is half full, the top half just has air in it. So that part will feel warm when you touch it, but the lower half that still has propane should feel much colder.So if it starts feeling cold about a third of the way down, that means you still have two-thirds of a tank left, and you’re probably fine.But if it only feels cold near the very bottom, it’s almost empty and you should go get a new tank before you start cooking.