what does it mean when my 2004 Buick Rainier says coolant to hot

Explanation should be in you owner's manual, I am afraid I am not experienced with the Rainier. Check here http://repairpal.com/automobile-owners-manuals-online or try this link you may be able to down load a free copy of the owner's manual for your vehicle http://www.autousermanual.com/

it is most likely overheating. you should get it checked asap before you do internal damage to the motor. check the coolant level to see if you need to add. Roy