Hopefully this isn't already obvious to everyone but me ... if nothing else, this may help explain some of the, "Oh my God, coolant is boiling out of my overflow bottle" threads.

With the ast cap off, adding coolant to the filler neck goes right to the ast and from there, if ast is full, straight to the overflow bottle... So unless you realize what is going on, it appears that you are successfully adding coolant to the motor... (you fill, the level slowly falls, you fill again...) when in fact you are just filling your overflow bottle. D'oh!

So... once your ast is full, cap it. Then continue filling. The cap stops flow to the overflow bottle, which allows you to get the coolant level up to the very top of the filler neck, which is necessary to completely purge the system of air. That last inch makes a big difference!

 

i like to squeeze (pump) the lower rad hose and then unplug the tb hose and then repeat like a jillion times.

 

Shouldn't matter if your AST is the highest point in the system, which it should be

 

I have stock AST and filler neck. Filler neck is higher on mine, as this flow definitely occurs (car was jacked nose-up, too).

Does make sense that AST should be higher tho...

 

Filler neck is highest on mine too. I ran into this as well, kept wondering where the coolant was going. I soooo hate our cooling system!!!

 

in theory the ast should be the highest point so it can catch all the airbubles. i wouldnt know i got rid of mine 2 years ago.

 

the cap on the ast should only let out coolant at 13 psi or whatever the cap is rated at

 

i put a new cap on my after market ast and when i fill up the filler neck it still goes by it and into my overflow tank and comes out of the rubber grommet. guessing i should get another new cap huh???

 

Throttle body is the highest point, not the AST. Heck, the AST isnt even as high as the filler neck. The reason it works to trap air bubbles is that the coolant flow will pull some bubbles with it, when coolant enters the AST it goes in toward the bottom and drains out the very bottom. The air stays in the top of the AST, getting pushed out the overflow hose when things heat up. When it is coolig off the AST pulls coolant back in from the overflow thus eliminating air from the system.

 

Now i know how to 'properly' charge my system...Thanks.

 

I know HOW it works, but you'll notice some differences when you make the AST the highest point

 

One thing that was worked for me was to remove the upper coolant hose to the throttle body. Thats the highest point. After filling the thermostat housing with coolant I would use my mouth to blow into the filler top till the fluids would start to come out of the hose at the back of the throttle body. Strange as it may be, this would prematurely push most of the air out of the system. Of course all this was done while the car was off. Once replacing everything back, I would start the car till it warmed up with the heater on. Once fully warmed up all I would have to do was top off the t-stat housing. In my experiance using the method would burp the coolant system in a matter of minuets.