Why does coolant spew out when I'm removing radiator pressure tester?

[Puhdantic]

I rented the tester at the link.

https://www.oreillyauto.com/detail/...ls-evertough-radiator-cap-test-kit/ren1/67085
I had to use one of the adapters to make it fit my filler neck. Once I finished with it, I twisted the paddle thing to release the pressure and a bunch of coolant started spitting out at the connection between the adapter and the pressure tester.

I made sure to twist the paddle in the direction of tightening so that it wouldn't inadvertently loosen the other connections.

 

[Silver]

If you didn't release pressure before you took the cap off, then, well... the pressure had to be released.

 

[jhs914]

You have air in the cooling system. Coolant won't compress, air will. When you pressurize the system with air it compresses and when you release the pressure the air expands and pushes some coolant out.

 

[Passport1]

Did you tell an insanely funny joke while you did that?

 

[Puhdantic]

You have air in the cooling system. Coolant won't compress, air will. When you pressurize the system with air it compresses and when you release the pressure the air expands and pushes some coolant out.

So this is normal? I lost probably 1/4c of coolant when I released the pressure.

 

[JohnnyG]

Sounds pretty normal to me.