---------EDIT------please read for changes...there are some better details and better explination on parts.
well for one... green isnt as good as red for whatever reason. different mix i think. i've been told bad things about what green coolant can do, and while its hard to believe what i heard (mucked up the surface of the coolant passages in the head) its worth the peace of mind to hit up a toyota dealer for a couple bottles of toyota red. the person that attested to green screwing with the metal was a reputable one, so if i remember correctly, i didnt doubt him. either way...u should spring for the red. and like its been said, do NOT attempt to mix them, nomatter what the bottle says about compatibility.
and the red looks pretty!! so get it.
i dont know about the underguard... dont have one. find the drain cock in your radiator and if there is no hole below it to drip then, yes. remove the thing and reinstall it once this whole ordeal is finished. even if there is a drain hole it will be hell though, because the drain cock will never spray straight down. in fact you should prepare to make a complete mess of yourself and the ground beneath your car, because you will miss the pan you're draining the stuff into at least once. take a minute and remove the underguard so you can see everything and access stuff easily. and aim.
you'll have to drain the coolant, fill with water, run it, drain it, (dont let it get to hot, watch the temp!) and repeat. i did this at least three times to fully clean the sludge and green coolant out of the engine block and passages because the water kept coming out brown (rust). but i didnt just flush it....
since you probably wont remove the drain cock on the side of the engine, you'll want to blow the water out of the system with compressed air to save time and do a better job. once you've ran the car with some straight water to remove sludge and such, make sure the fluds are sufficiently cooled, remove the lower radiator coolant hose, remove the top radiator hose, and use an air compressor to blow out most of the water left in the engine - but take CARE you do NOT want to put lots of pressure into this and dont think i mean seal it tight with duct tape and blast in 130 psi. just hold the top hose and spray some air into it. dont use your mouth and lungs. this stuff is poison, so you dont want it NEAR your mouth or risk backpressure splashing some into your mouth...so use an air compressor, and apply a low pressure until water begins to drain, and do that/adjust your pressure until water stops coming out. i do not know how delecate the heater core is, and excessive pressure is not good, i dont know what the system commonly runs at. this method is quick and saves you removing the block drain cock. replace hoses, fill with water, run it, drain it, and see how clear the water is. repeat the drain and air-compressor part again if the water is really dirty, and check the clarity once more. once you get the water clear or as close as you can, stop flushing, check all your hoses, fill with antifreese (toyota red) and then distilled water (better than tap in some locations where there are lots of chemicals and sediments).
run the car and burp the system of air. now you're full of toyota red and good to go.
