BlackBirdRyder02

iTrader: (3)

do ls1's 99-up have bleeder screws for anitfreeze flushing if so where it would be located

TAtoad

iTrader: (22)

when i've been under the car i think i've noticed a drain plug on the radiator

LS6427

iTrader: (2)

Use the drain valve on the bottom drivers side of the radiator.

Best/easiest way to flush and get every drop of old coolant out.
Cold engine.
Remove radiator fill cap.
Remove the t-stat. (2-3 minute job)
Put t-stat housing back on. (1 minute)
Take the entire radiator drain valve (petcock) "off", don't just open it. It'll drain faster with it off and thats what you want. ((Buy a new petcock, sometimes they break when you remove them all the way, they're like $2.00))
Take a hose and stick it in the radiator fill cap, running medium to high.
Start the engine.
Let it run for about 15-20 minutes or until the water is running out the drain CLEAR.
When it does your entire system is clean.
Put the t-stat back in.
Put the drain valve back in. Use the new one, what the hell.
Put half a jug of Dexcool in the radiator. (Or if you live in very cold places, 1 ½ jugs of Dexcool)
Fill the rest with water. (one bottle of water wetter can't hurt, your choice)
**Let it run and warm up till the t-stat opens once and starts to flow, to see if the level drops, just to make sure the system is completely full of coolant, if it drops just top it off. Then wait one more time for the t-stat to open and start to flow, then top it off again.**

Done.

If your system is sealed, don't mess with it for another 5 years or more.