Answers to assorted questions from Bill and others:
Originally Posted by bill buttermore
Andy, do you pull the thermostat to flush it? And, isn't flow into rad at top, out at bottom?
-- I think normal flow is indeed from top to bottom (I think the Impala SS had it the other way around, but that'* kind of an unusual case), but what we're doing here is a backflush. Well, that'* how Prestone describes it on their packaging, although I'm not sure _that_ term is correct either; I rather doubt that plugging a garden hose into your heater line is enough to get everything going in reverse, but in terms of injecting fresh clean water into your cooling system and _pushing_ all the old mix out of any and all convenient openings that you've made (e.g. radiator petcocks, removed lower radiator hose), you can't beat it with a stick. In other words, normal direction of coolant flow isn't the point with this technique; it has more to do with performing as thorough a flush as possible, which achieves more than what a really thorough gravity drain alone can accomplish. You want to push the sludge out; it'* not going to all get carried off when the old liquid is drained.
-- I installed the flushing tee in the lower of the two lines going into the firewall just inboard of the right-side wheel well. The surge tank has to come out first. The upper hose can be flexed out of the way enough for you to cut in the flushing tee into the lower hose (actually you'll be cutting out about 1" or so of hose to accommodate the body of the flushing tee, so that you don't distort the geometry of the pre-formed heater hose), and the garden hose can connect to it straight down from above for flushing. The tee stays permanently installed, so you have a lot less hassle next time.
-- The flushing kit can be found at the usual auto-supply places. They usually give you two or three different sizes of tee, two of which won't fit: IIRC, the 1/2" diameter will fit some imports, the 5/8" diameter fits the Bonneville, and the 3/4" fits some Fords and maybe assorted SUVs and such. While you can buy flushing tees separately, you still need the garden-hose adaptor that comes in the kit (a female-to-female garden-hose connector with a one-way valve in the middle), along with an extension pipe that clips into the radiator neck to divert overflow water wherever you want to aim it.
-- I remove the lower radiator hose clamp at the radiator and pull the hose off to drain the old coolant. I then press the hose back on and leave it there without clamping (friction will hold it on), start the garden hose running, and start the engine. During the flush, water will eventually backfill the radiator and start flowing out the top. After a minute or two of this, while everything is still running, I pull the lower hose off and allow a great big rush of water and sludge to come out (the garden hose _is_ still pumping water _in_ while this goes on), and once the initial rush subsides (takes only five seconds or so), I press the hose back into place, let the radiator fill to overflowing again, and repeat the whole process. I repeat this maybe five or six times, until the flood of water from the lower hose is coming out clear. It'* easy to see when your flush process is complete.
-- I don't remove the thermostat for this; in fact I don't disturb it at all. The amount of crud that'* coming out anyway, a good portion of which has been propelled out by the garden hose that'* up at the heater-core end of the system, and the fact that the radiator gets backfilled via the lower hose during this process anyway, suggests that removing the thermostat wouldn't really gain you anything.
It does make rather a mess everywhere, and I'm always careful to hose away any standing pools of old coolant, but if you catch the initial coolant drain in a bucket for disposal, you should be okay; the coolant residue carried off in the flush water is much more diluted than what was circulating in the system when you started.