2000 K2500 7.4L AT 4x4 Now that the lifter noise is gone, (Seafoam is the best!) I can hear water rushing behind the dash. At first I thought it was a leaking heater core, but I notice the noise when the thermostat opens. When the engine starts to warm up, that is when it sounds like water rushing through the dash. I have noticed low coolant, but I can not find any leaks on the ground. I am guessing there is an air pocket. I also have noticed the oil fill cap has a green color on it. I suppose that means a head or intake gasket? I was going to pull a few plugs and check them for color. What do you think?