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Discussion Starter #1
What can cause a empty overflow tank. My radiator is always full with coolant.
 

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If it was full and now it's empty then there is a leak somewhere. As coolant expands when hot it flows from the radiator into the overflow. Then when it cools it gets sucked back into the radiator from the overflow. It's a closed system so in theory the levels shouldn't change over time.
 

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Discussion Starter #3
If it was full and now it's empty then there is a leak somewhere. As coolant expands when hot it flows from the radiator into the overflow. Then when it cools it gets sucked back into the radiator from the overflow. It's a closed system so in theory the levels shouldn't change over time.
I added some water in there for the time being. Keeping a eye on it every other day I drive it. Could've been a bad bleed from my recent timing belt work...

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Discussion Starter #7
Is it? I thought the top of the overflow cap had a hose that vented down to the atmosphere, so perhaps evaporation could eventually cause the tank to be empty.
Yes indeed. The factory overflow have 1 tube leading outside and 1 connected to the radiator spout.


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Discussion Starter #8 (Edited)
After filling up overflow tank last night I let the car warm up this morning preparing for work (20 mile commute there and back). Came back and overflow tank still topped off. Picture shows how rad coolant always look since I got it.


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Is it? I thought the top of the overflow cap had a hose that vented down to the atmosphere, so perhaps evaporation could eventually cause the tank to be empty.
Good point! Closed system was a bit strong of a term...not like the older BMW systems where the overflow tank is actually pressurized.
 

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Definitely keep an eye on it over time! It could be a very very slow leak, or just evaporation. It might have never been messed with before in the almost 20 years.

Though, I hope you dind't just add green coolant to the system like that without a complete flush unless it already had green...

Good point! Closed system was a bit strong of a term...not like the older BMW systems where the overflow tank is actually pressurized.
It's all good, I was genuinely asking curiously because I wasn't sure if mine was broken or something LOL. Mine has a hose that just goes down there, but when I got the car, it had originally been sliced shorter by the belt I think or something, so I wasn't sure if it was supposed to be connected to something or not. I never had any troubles, but if it is supposed to be a closed system, I'd want to fix it. Or maybe the overflow tank cap has some sort of valve to keep the system closed unless a release is needed. But I didn't think it would be all that complicated.
 

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Discussion Starter #14
Definitely keep an eye on it over time! It could be a very very slow leak, or just evaporation. It might have never been messed with before in the almost 20 years.

Though, I hope you dind't just add green coolant to the system like that without a complete flush unless it already had green...
It was green from previous owner. It doesn't seem like a mixture of any kind so I believe its a complete flush. And yes it has been messed with because previous owner installed a spectra radiator. Not sure if the thermostat been changed.

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Discussion Starter #15
Just a follow up to my empty overflow issue. When I last time filled it up with water, it hasn't went down since driving it.
 
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