Maybe this will help, it's from a past DT Thread.
If you're hearing water running though your heater core, you have air in the cooling system. You need to park the truck in the driveway with the nose sitting higher than the rest of the truck. While the trucks engine is cold, get under the hood and remove the cap. Start the truck and put the heater on high-heat. Double check the level in the bottle and fill it up to the cold mark. Now just let the truck idle while it warms-up slowly. You need to be careful here because if the system has an air pocket, it could flash-boil on you. If it does that, it’ll push coolant out like “Old Faithful”; so be careful. As a safety measure, you can put the cap on but leave it loose. That way if it flash-boils, it won’t hose you down with hot coolant; not fun! As the coolant flows though the bottle, you can feel when the thermostat opens as the upper hoses gets hot. You need the thermostat to stay open a number of times because it the only way to get the air out of the system. Check the gauge on the dash from time-to-time and when you’re sure the coolant is hot, the thermostat has open-n-closed effort times, and the level in the bottle is full to the hot fill line, you can bet the air is out of the system now. Tighten the cap. Turn the heater off and you’re done purging air from the coolant system. There’s a purge tap on top of the engine but if the bottle is sitting higher, it’s the better choice. I’ve never be able to use the bleeder tap without getting hot coolant all over me and the whole engine. That and I hate the feel of coolant on my arms and hands.
Now you can check the cooling fan. Nothing is harder on the cooling system than the time the vehicle is sitting still with no air-flow though the front of the vehicle. When you first start the truck, you won’t hear the fan after the first few seconds. But as the truck just sits there, the air flow though the radiator gets hotter, and the fan clutch begins to get a little heat into it, the clutch will began to lock-up. You should be able to hear the fan pulling air though the radiator. Keep checking the gauge on the dash and watch where it peaks. Where does the gauge set as you drive down the road? That’s about where the needle should be now as your truck just sits with the engine idling. If the trucks temperature keeps climbing, you could very well have a bad fan clutch.
Move you hand across the face of the radiator. Check for cold spots or areas that seem much hotter than the rest of the surface. If the temperature isn’t uniform, you could have a plugged radiator core. Stop leak products have a bad habit of plugging good and bad areas within the core.
After checking all of this and the system just seem to be running too hot, you could have a thermostat that’s not opening fully. Checking or testing it will take more time than the thing is worth. They’re pretty cheap so just replace it. If you’re going to take the time to replace it, you need to make a choice; do I flush the cooling system or use the old coolant. And since you think there maybe stop leak in the system, you need make a choice about using an acid flush though the system. The acid flush should clean that crud out of the system. If you use the acid flush, you need to remember to open up the heat core as well.