Why is my radiator maintaining pressure for a long period of time?

[alacran1]

Every time i want to check my coolant i remove my radiator cap and BAM! coolant gushes out the cap.

 

[jetjock]

Physics is a harsh mistress...

 

[IndigoMKII]

try not checking the coolant when the system is pressurized

 

[hvyman]

Ya. You need to wait till the pressure bleeds off. Squeeze the rad hose first. Auto basics.

 

[jetjock]

Not supposed to be taking the cap off.

 

[alacran1]

Oh i forgot to add it happens even when the engine is cold.

 

[Rollus]

Is cold one hour or one day after?

 

[jetjock]

Ya. You need to wait till the pressure bleeds off. Squeeze the rad hose first. Auto basics.

Or use the cap like it was designed to be used. It has two positions for a reason. Then again:

Not supposed to be taking the cap off.

 

[IndigoMKII]

What JJ is trying to say is, the coolant res is there for a reason. When the coolant gets low it creates a draw on the coolant res pulling and filling the coolant system as needed.

 

[jetjock]

Right. In a pressurized fully closed type system the radiator is always kept 100% filled by the reservoir. Therefore the tank is an extension of the coolant level. As long as everything is working there's simply no need for removing the cap. The less it's messed with the better.

 

[Nick M]

Every time i want to check my coolant i remove my radiator cap and BAM! coolant gushes out the cap.

Have you noticed all the threads here with the opposite problem?

 

[jetjock]

I've never seen coolant gush out the cap. The radiator may need to be jacked down...

 

[Rollus]

Maybe the cap doesn't work properly. If it doesn't open, pressure won't go in the overflow tank.

 

[jetjock]

Huh? Not following you there Mon sewer...

 

[Rollus]

Sorry, english is not my native language.

If my understanding is good, the cap has 2 functions:
A check valve let coolant going from expansion tank to radiator under vaccum
A pressure valve (0,9bars or more for aftermarket cap) let coolant going back from radiator to expansion tank when radiator is under pressure.

If the pressure valve don't work, radiator (and the whole cooling system) remains under pressure. That's what I tried to tell by "if it doesn't open" in my previsous post

BTW, we don't know what is the pressure for BAM! coolant gushes out the cap...

 

[Backlash2032]

I think what he's trying to say is the cap won't let the coolant back into the radiator as it cools, but that would create a vacuum..

 

[Rollus]

No, I mean that cap won't let coolant go in the tank when engine warms, and that create a pressure.

 

[alacran1]

The problem seemed to go away now that i squeeze the upper hose couple times.

 

[jetjock]

Now that's entertainment...

 

[IndigoMKII]

The problem seemed to go away now that i squeeze the upper hose couple times.

Um? I bet this problem goes much much deeper than this.