# Coolant level rises slightly in reservoir when radiator cap removed in cold car?

**URL:** <https://community.cartalk.com/t/coolant-level-rises-slightly-in-reservoir-when-radiator-cap-removed-in-cold-car/182936>\
**Category:** Maintenance/Repairs\
**Tags:** nissan, rogue\
**Created:** [March 11, 2022, 1:53pm UTC](https://community.cartalk.com/t/coolant-level-rises-slightly-in-reservoir-when-radiator-cap-removed-in-cold-car/182936 "2022-03-11T13:53:50Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![luciagifford\_176409](https://avatars.discourse-cdn.com/v4/letter/l/3be4f8/32.png) [@luciagifford\_176409](https://community.cartalk.com/u/luciagifford_176409)\
**Post date:** [March 11, 2022, 1:53pm UTC](https://community.cartalk.com/t/coolant-level-rises-slightly-in-reservoir-when-radiator-cap-removed-in-cold-car/182936/1 "2022-03-11T13:53:51Z")

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Is it normal in a cold car (off for many hours) for the coolant level to rise slightly into the coolant reservoir when the radiator cap is removed? It rose maybe 1/4 of an inch but I thought there is supposed to be no pressure when a car is off and cold car.

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**Author:** ![texases](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/texases/32/862_2.png) [@texases](https://community.cartalk.com/u/texases)\
**Post date:** [March 11, 2022, 3:45pm UTC](https://community.cartalk.com/t/coolant-level-rises-slightly-in-reservoir-when-radiator-cap-removed-in-cold-car/182936/2 "2022-03-11T15:45:11Z")

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If there’s even slight pressure this is what I’d expect to happen. Is this a pressurized coolant reservoir when the engine is hot?

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**Author:** ![shanonia](https://avatars.discourse-cdn.com/v4/letter/s/9de053/32.png) [@shanonia](https://community.cartalk.com/u/shanonia)\
**Post date:** [March 11, 2022, 6:47pm UTC](https://community.cartalk.com/t/coolant-level-rises-slightly-in-reservoir-when-radiator-cap-removed-in-cold-car/182936/3 "2022-03-11T18:47:47Z")

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> [@texases](#):
>
> Is this a pressurized coolant reservoir when the engine is hot?

Probably. If the reservoir was vented all the time, the level in there could vary any time, not just when the system was depressurized.

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**Author:** ![Purebred](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/purebred/32/46796_2.png) [@Purebred](https://community.cartalk.com/u/Purebred)\
**Post date:** [March 11, 2022, 7:32pm UTC](https://community.cartalk.com/t/coolant-level-rises-slightly-in-reservoir-when-radiator-cap-removed-in-cold-car/182936/4 "2022-03-11T19:32:40Z")

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My WAG, when cap is opened, hoses slight contract raising the coolant level in the reservoir l