see how much coolant to put All I see is HOT and COLD . I don't see any lines that say stop here. OR LOW OR HIGH. It's a 99 Buick Century with a Low Coolant light on.

Have someone help you to remove and replace the radiator cap. Coolant should be to the top when cold. Add if needed and wait a while for the passages to fill and balance. Fill the recovery tank to "Cold" level. Run the car for a while or take a short trip. Wait until the defroster air is warm. Then let the engine cool for an hour or so and recheck everything. You could have an air pocket somewhere.

The hot line is where you fill it to when the engine is hot and the cold line is where you fill it to when it's cold. Don't worry about putting in a little too much.
If the radiator is really low, you need to take the cap off when the engine is cold and fill it there first.

Pour coolant into the reservoir until it reaches the Cold line. If the Low Coolant light comes on again in a week or so, you should get your system checked for leaks.

it's usually a plastic tank with a hose attached to the top filling hole of the radiator. FIRST SHAKE THE ONE GALLON JUG OF ANTI_FREEZE BECAUSE THERE ARE CHEMICALS IN THERE THAT CAN SETTLE TO THE BOTTOM> SOME OF THOSE CHEMICALS ARE CORROSIVE< THEY HELP KEEP YOUR RADIATOR CLEAN. second off you mix ant-freeze wiith water a 50/50 mix is usual. take the lid off the plastic tank NOT THE RADIATOR fill the tank to the cold line if the engine is cold. then continually check it once a week for a few weeks to make sure it stays in that area. try not to fill the radiator.
buy one gallon, get an empty 1/2 gallon juice bottle. fill the juice bottle up. once it's full that will leave you with 1/2 gallon antifreeze in the 1 gallon jug fill the jug with water and you now have a 50/50 mix. if worse comes to worse just fill that plastic tank till it's about 1 inch from the top.
good luck.

[EagleAutosports]

They all said it all on this one.