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Dg2028
Samba Member
Joined: September 11, 2018
Posts: 34
Location: Motor city
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 Posted: Sat Apr 27, 2024 6:24 pm Post subject: What stops coolant from flowing out when you take the cap off? |
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| Just wondering why coolant doesn't flow out the expansion tank when you take the pressure cap off, when the engine is off and the cooling system is full. If you opened the air bleed on the radiator with the cap off and engine off, would coolant then flow out? |
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zerotofifty
Samba Member
Joined: December 27, 2003
Posts: 1655
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| Posted: Sat Apr 27, 2024 7:29 pm Post subject: Re: what stops coolant from flowing out when you take the cap off? |
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Assuming a level van, 1. Vacuum, the fluid wont flow as there is not way to get air in to the radiator to displace the lost fluid. 2. I assume so, once bleed petcock on radiator is open, fluid may then flow out any opening below the fluid level in the radiator.
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E1
Samba Member
Joined: January 21, 2013
Posts: 6662
Location: Westfalia, Earth
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| Posted: Sat Apr 27, 2024 7:44 pm Post subject: Re: what stops coolant from flowing out when you take the cap off? |
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| Dg2028 wrote: |
Just wondering why coolant doesn't flow out the expansion tank when you take the pressure cap off, when the engine is off and the cooling system is full.
If you opened the air bleed on the radiator with the cap off and engine off, would coolant then flow out? |
It *will* flow out if hot and sometimes when just still warm — before it cools and contracts. If all’s correct, by the time it’s cooled it will vacuum back in the same amount of coolant that expanded from heat to the overflow tank.
When the blue cap goes bad, it won’t hold high pressure and will allow excess coolant expanding into the overflow when at full-hot, sometimes overflowing out its top vent, and typically well beyond the amount the vacuum can retrieve.
No, coolant will only flow from the radiator tap when hot and under pressure.
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