pull out your plugs, hook up a pressure gauge to your coolant tank, apply 13psi. Wait a little bit. crank your engine and watch the water shoot out of the spark plug hole. the hole that it shoots out of is where ther leak is. If it is a small leak, you could twist up pieces of paper towels with tape and stuff them down the plug holes, which ever one is wet on the end is your leaky cylinder. Change the oil if you plan on driving the truck anywhere, ccolant in your oil will ruin the bearings