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Message: <blockquote data-quote="Richard L" data-source="post: 1001989" data-attributes="member: 52972">Kate,Yes, you should have some fluid in the coolant overflow reservoir.  After a coolant flush the normally refill the coolant through the radiator.  This will often leave an air bubble trapped in the cooling system and may take several heating and cool down cycles to burp the air out of the cooling system.  When the air is expelled, the engine is at operating temperature and the cooling system is at pressure.  When the pressure reaches the radiator cap limit, a valve in the cap will allow the expanding coolant and trapped air to be pushed into the overflow tank where the air is burped out.  When the engine cools the coolant contracts and the coolant in the overflow reservoir is sucked back into the engine to make up for the heat expansion and air that was trapped.If your reservoir is emptly, you will most likely suck air back into the cooling system, which is not a good thing since air does not absorb as much heat as the coolant and can lead to hot spots in the engine.It's not a critical issue, but I would go back and ask the shop that did the coolant flush to top off the system and make sure there is some coolant in the reservoir...more when the engine is hot and less when the engine is cold....Rich</blockquote>