I finally had it with this low coolant thing and decided to pour water in the AST and the white overflow container. I start pouring in the white bottle and I see green liquid on the floor. Could this be the reason for my low coolant. There was still coolant in that container since it came out green. I think if there's still coolant in that tank, it won't cause low coolant. What do you pros think?

 

In a word, yes.

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mostlikely, if its always full then the radiator cap needs replace. the spring is weak and cant handle the pressure.

 

I had the same problem exactly. I took a flashlight and it looks like the neck of the white plastic overflow tank has corroded through. Oh yeah your car smell like coolant for days now.