Should the coolant cap on the plastic bottle hold pressure on a cold engine?

When I open the cap, (engine sitting overnight) I get a big WHOOSH and the coolant level jumps up an inch in the bottle.




I always thought the system should allow air back into the coooling system as the engine cools.

 

On a sealed system yes it will hold pressure even after sitting all night.

Yes you have a sealed system.And it will hold pressure.

 

So,,,

How does a shadetree mechanic like me make sure there is not too much air in the system?

(idle the engine with the cap off?)

 

That doesn't always work the proper pressure can't be met and it will overflow.

The air will bleed out by itself.

 

Good to hear that the air will bleed out from the over flow plastic bottle. In my previous BMW 325i, it was a bid problem to bleed out the air from the system. Sometimes we had to bleed it for days....

 

Where?

(I sure am inquisitive, huh?)

 

It will get out don't worry.

There is not a problem with any of the 4 cylinder cars with bleeding the system.