Where is the valve to drain the coolant from the system on a 2000 Buick Century, I need to flush the system..

That stuff is the long life coolant breaking down, flush the system and install the newer more stable coolant.

by the sound of it your system needs flushing,if u have a user manual look and see if it tells u how to otherwise get back to me

If you're losing coolant you have a leak. Go to the shop that flushed your system and have them check for leaks. They may have left a hose clamp or a drain bolt lose.

Hi, if there is not a petcock or plug at the bottom of the radiator, you can just remove the lower radiator hose to drain the coolant. Many cars do not have drain plugs. Please let me know if you have more questions and thanks for using FixYa.

take the bottom hose off from the radiator

You need to drain the old antifreeze and flush the entire cooling system with a commercial product such as Prestone Super Flush. After flushing according to the directions on the product you will want to fill the cooling sysstem with plain water and let it circulate through the system. Drain the system again and repeat the process until the water is clear of any antifreeze. Refill the system with the proper mixture of antifreeze. Make sure you use a quality antifreeze that is compatible with your make and model of car. The auto parts store personnel can help you select the right antifreeze. DO NOT refill it with Dexcool. That is the antifreeze that GM put in originally that is causing the problems. Dexcool not only forms a gummy sludge in the cooling system, it also attacks certain gasket materials and causes coolant to leak into the engine. Hopefully, this hasn't happened yet.

yes there is a small plastic plug on the bottom of the radiator.make sure car is cool.

I’m happy to help further over the phone at https://www.6ya.com/expert/kenneth_3efc1f8510674f04

UNDO THE BOTTOM RADIATOR HOSE AND DRAIN IT OUT.. THEN GET SOME OF THAT BOILING TREATMENT AND LET THAT IDEL FOR 15 OR 20 MIN.. THEN PUT IN NEW COOLENT

The drain should be on the drivers side at the bottom of the radiator, facing the driver. It's a plastic "wing" that unscrews. There should also be a bleeder for exhausting the air from the system when you refill. The bleeder I'm familiar with is a brass screw screwed into the thermostat housing. (where the top hose attaches at the engine)

The coolant level sensor is located on the radiator. If you are looking at the engine from the front of the car it will be on the left side. There will some kind of clip holding it in the radiator. Removed the clip and pull the sensor out. You will lose coolant so try to swap it out quick or drain some of the coolant out. Once new sensor is installed, install clip to keep the sensor in place and reconnect the wires to the sensor. Crank the engine and make sure the coolant level is full. This should correct your problem.