Remove the lower radiator hose and get wet.
Remove the upper hose.
Run your garden hose through the radiator until it comes out clear.
Remove the t-stat, stick your hose in there, run until clear.
Leave t-stat out adn put it all back together and fill it with water.
Idle engine with heater on for 20 min or so, leave radiator cap off and keep system full.
Let cool, drain, repeat until all comes out clear.
Refill with your favorite aluminum safe coolant in a 50/50 mix.
DO NOT use your garden hose to mix the coolant, you MUST either buy it premixed or mix it yourself with distilled water.
You may want to buy a over the counter cooling system flush chemical to help break up any clogs.
This would also be a good time to change all of your hoses.
If you need to drive it in the mean time remove the t-stat to keep it from overheating.
Better that than to blow the engine.

 

I got an electric fan mounted in the shroud in 1 of my trucks and viscous in the other. Electric is definately working better for me economy/power wise. Also easier to work on when you need to work on the front of the engine or radiator. Just unplug fan and out the shroud comes.

 

get a radiator flush kit, they are cheap and make it super easy, the hose screws to the kit making a better flush.