Where does Engine Coolant Go?

Typically you'll only ever remove the "silver cap" atop the radiator when you've completely drained your coolant and refilling... If you're topping off always put the coolant in the overflow bottle (the one you're seeing with the black cap). The coolant under the silver cap is under pressure when the vehicle is hot/warm. If you remove this cap you're going to either make a mess or severely burn yourself (unless the car is cool). In addition you'll also be introducing air into the cooling system which will typically have to be "burped" out. Finally, you'll find the radiator is more than likely completely full (unless your overflow is completely empty and therefore the system as a whole is low).

So in summary, if you're just topping off ignore the radiator and add directly to the coolant overflow bottle. Oh yeah, you can open up the coolant overflow bottle at any time...even when the vehicle is hot because that bottle is not under pressure.

Mike

 

Yeah, air in the system makes the coolant rise and fall sporadically. That's what I was referring to when I mentioned burping the system. Some cooling systems have a bleeder screw at the water pump, most do not. Typically I'll start a cool engine with the silver cap off and keep it topped off. After several minutes you'll see the coolant level drop slightly then a few air bubbles will come out (that's the burping part) after you see that the coolant level will rise very quickly and that's the point I'll very quickly secure the silver cap... that's the way I get the air out of the system and works every time (although I've never done it on a Prius).

Mike

 

The engine coolant goes into the overflow tank. Only use the radiator cap to initially fill. Make sure the tube from the radiator cap neck to the overflow tank is in good shape, otherwise it defeats the purpose of having an overflow tank

The best way to purge air from a cooling system is to use a vacuum bleeder. The gadget mounts in place of the radiator cap. Shop air is then put through a venturi to create a strong vacuum in the system. Any air pockets are collapsed, and fresh coolant is drawn in