HOW-TO: Easiest way to hot-flush your cooling system in your own driveway.
This works really well to get old, oxidized dexcool sludge out of a cooling system (common problem in late 1990's to 2000's GM vehicles), but it also works for oxidation/scale buildup in older vehicles... This is not a cure for overheating, or a legitimately clogged cooling system, and obviously you need to keep an eye out for leaks during and after this process.
The simple "easy hot-flush" process:
1. Run the engine until it's warmed up, dump the coolant out of the block, refill the block with warm water and let it cool with the water in it.
2. Pull the t-stat, put it back together except for the upper hose, garden hose in the radiator and start the engine.
3. Run it until it comes out clear, pull garden hose out of radiator and shut off the engine the moment it runs out of water. Reinstall hoses.
4. Refill with chemical flush mix and clean water, burp/bleed it until it's completely full, then roll down the windows, crank the heater all the way, and take it on a "spirited drive"... AKA beat on it like it's stolen AND owes you money. Get it as hot as you're comfortable with, then park it and as soon as it's cooled down to the point where you wont die, relieve pressure and dump all that nasty garbage out.
5. Let it cool down enough to refill it, put another bottle of chemical flush (or switch to citric acid solution), refill with clean water and burp/bleed again.
6. Repeat until the dump comes out mostly clear.
a. Second dump should be much cleaner than the first, this process usually only takes two cycles to get 95% of the buildup out of most vehicles 30 years old or less. Neglected vehicles will probably take three cycles.
b. Older vehicles could take up to three cycles, but if there's still a bunch of crap coming out after the fourth cycle there's probably a clogged water passage and a change of tactics is required.
7. Once there is a reasonable confidence that the cooling system is no longer heavily contaminated, allow the engine to cool completely.
8. Pull the upper radiator hose off of the radiator, leave it attached to the t-stat housing. Pull the lower hose off of the water pump inlet, leave it attached to the radiator.
9. Pull both heater hoses off of the engine. Remove any coolant/crossover/bypass pipes from the engine. (Clean separately)
10. Run the garden hose into the heater core and radiator in the reverse direction from normal coolant flow.
11. (Optional) Use two old 1 gallon pitchers, a large funnel, and extra lengths of hose, reverse flush the heater core with 1 gallon mix of clean hot water and chemical flush. Rinse with clean water.
12. (Optional) Remove radiator and reverse flush it with (more than one) gallons mix of clean hot water and chemical flush. Rinse with clean water.
13. Pull the belt off the water pump pulley, if the water pump is under the timing cover skip this step.
14. Run the garden hose into the t-stat outlet and spin the water pump pulley backwards by hand. This may seem pointless in some cases, and in some cases it is pointless because some water pumps will not pump backwards. But in some cases the water pump will pump backwards, and it will reverse flush the engine block. In all cases, this can potentially illuminate problems with the water pump, such as play in the shaft or broken/missing/corroded vanes resulting in an inefficient water pump.
15. Put everything back together, with a new t-stat and fresh coolant concentrate of your choice. USE ONLY DISTILLED WATER. Anything else and you're shooting yourself in the foot, making all the work you just did utterly and completely pointless.
Enjoy your like-new, hot-flushed cooling system and marvel at how little physical effort you had to expend to achieve this.
NOTE: At any point during this process your vehicle could develop a serious coolant leak, due to the removal of buildup that could be sealing any holes or cracks that have been present for a while. If this happens, stop the process and repair the leak immediately.
