hi sages- have a couple of questions on modern cooling system cleansing. vehicle is a 2000 chrysler sebring with the v6 engine,100k miles. all systems and running , heating, cooling are operating ok, no leaks. problem is when viewed from the radiator cap hole, coolant is very rusty and a little sludgy with accumulated rust. Q#1 should i add a can of flushing fluid and run it for a while and drain and refill with 50/50 af like in the good old days. uncle moe tells me the flushing fluids are useless and may harm todays pump seals and aluminum innards. what do you folks think? also in the so called good old days of rear drive cars without interference engines you would put a garden hose onto a plastic tee in the heater hose which you just installed and run fresh water through an idling engine which would blow out through the radiator cap or through the disconnected lower radiator hose. after a few minutes of clean blowout you would close and reconnect everythingafter most of the fluids had drained ) put in 50/50 af and maybe a can of rust inhibitor/waterpump lubricant and be done. the chrysler dealer who wants to make a 3 figure home run onthis job told me the tees arent used anymore and recommended his power reverse flushing machine. my approach would be to remove the stat for free flow, run fresh water through the radiator cap hole with the engine idling and let it blow out through a disconnected lower radiator hose until clean. maybe removing the stat is unnecessary. kindly give me a critique and whether i have left anything out. your advice is always on point. thanks tons bob f

I have never disconnected a lower hose for this, usually a heater hose instead and put the garden hose on the nipple from which you unhooked the hose; I have an old garden hose with 1 end cut off just for doing coolant flushes; on engines that have them I also pull the block drains and poke thru any crusty buildup that may be there and let the crap drain out theer til the water is clean/clear. as long as you have a constant supply of cold water it WILL NOT overheat; but I'd think that the water could escape faster than a garden hose could supply if you do it by the lower rad hose.

I've always used your old technique; I've always used a mild rather of soapy flush and never tried the much stronger caustic ones. I've never seen the mild flushes hurt anything that I could see, but they never removed much inorganic crud either. Removing the thermostat to properly clean/test or replace it is probably a good idea; my experience is that some older thermostats seem to just up & fail, also radiator caps often get flaky after just one good overheat.

Note that the thermostats' air bleed hole often gets plugged entirely - that can cause a dramatic, but temporary, overheating until the system burps all the air out.

If it was me, I'd probably try the strongest flush I could find and then pressure test the system; if the heater, radiator, or pump goes, just figure they were about to go anyway. I seem to remember that Bar's Leak claimed to have an abrasive action to clean out the system over time - I've run it for years w/o a problem, but whether the system is cleaner that it started is hard to say.