What would happen if you open the radiator cap while the engine is hot?

Question

I have NO intention of doing this. I just know you have to wait till it cools before you open it. I'm just curious.

Answer 1

Thats pretty close to what would happen except all the dramatics. The liquid in there is around 200 degres and it would come out and burn you pretty bad.

Answer 2

Hi there,
The radiator cap helps control the boiling point of the water within the water system, the cap will release any excess pressure if the system overheats and boils over(usually when there is a fault) the system pressure is approx 15psi when hot and if you were to remove the radiator cap when hot it will throw out hot boiling coolant under pressure and trust me it gets everywhere. Check the coolant level when it is cold, if you have to check the level when it is warm wait at least 10-15mins before removing cap.
Hope this helps

Answer 3

Actually there's a pressure release that holds the cap on, so even if the radiator were overheating, the cap would stay on and spew hot water and steam from the sides. Also there's usually an overflow that catches extra hot water in a container, so in general it's safe if the car is hot.

Don't do it if the engine is overheating.

Answer 4

Jen..I did it once on be half of my mother busting my balls ..and when I did the ain't freeze shot every where..I was pissed..my mom can bust balls with the best of them..never open a radiator when its hot..its under pressure and will come flying out..there are radiator caps with a pressure relief valve on them...its suck..and I was covered in antifreeze..the water pump went on the car..and my mother...what else can I say I was only a teenager at the time..

Answer 5

I would highly warn against doing that even on accident as some would say. Exposing you lungs to large amounts of antifreeze vapor can be fatal to you health. Imagine, if a cap full of that stuff inguested can shut down your kidneys imagine what it could do to your respitory system if too much of that vapor is inhaled. Be careful.

Answer 6

Basically, the fluid will explode out of that opening. I have seen it done once. It can cause serious burns if it is hot enough.

Answer 7

if you have to open i suggest don't open reserve tank 1st then with a glove then a dry rag & stand to one side u should be right to open be careful

Answer 8

Boiling water would spew all in your face, then instantly your face would begin to peel off, your eyeballs would not be used to see anymore they would be donated to science.