A mechanic's advice that you won't forget when opening the coolant cap: "It's the same as in the kitchen with a pressure cooker."

Without a doubt, one of the great unknowns in our car is the coolant reservoir . We rarely look at it, rarely open it , and it even scares us with its warnings. And we're not going to discover here what coolant or antifreeze is for , which is basically to maintain a uniform temperature in your vehicle's engine , but rather we'll focus on those warnings and what they do. And all thanks to one of the latest videos by Juan José, one of our go-to mechanics on TikTok, thanks to his instructive classes from Talleres Ebenezer (almost 264,000 followers). And the big question: "Why can you never open the coolant cap when the car is hot?"

Juan José explains this by making an analogy with how a pressure cooker works : “It's because of the pressurization of the cooling system . To get the water to a certain temperature, the coolant can be set to 130 degrees. It needs pressure, just like a pressure cooker. If it didn't have pressure, the water would evaporate prematurely,” Juan José explains in the video.

And the cap is like the relief valve on a pressure cooker. Hence the warnings not to open it while it's hot. This, moreover, is a nearly impossible mission due to the pressure: "The cap will be calibrated to a specific pressure. Therefore, if you exceed the coolant level , before something bursts, it's ready to open and release that excess," recalls the Talleres Ebenezer video.

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Juan José then warns us about what would happen if we opened it while it was hot. The cap's warnings aren't just a whim of the manufacturers: "Before removing the cap, look inside the engine for the coolant tube. If it's softened and you can squeeze it with your hand, there should be no pressure in the circuit, so you can open it relatively safely," he warns. Another thing would be if it's too hot : "We do it slowly, very slowly, to give it time to equalize. If we see the water starting to bubble, we cover it and wait," he advises.

But knowing this doesn't come without its fair share of scares, especially with Japanese motorcycles and cars : "If your car has a radiator cap, which is typically found on Japanese cars, never take it off, really. Just like with motorcycles, never take it off. One turn and the cap flies up, the water comes out boiling, and if it hits your face or skin, it'll scorch," says Juan José. "You wait for it to cool down. But it's really very dangerous . It spurted on my face from a motorcycle that wasn't very hot, and my face was red for about three weeks," recalls the mechanic. We'll have to trust the warnings after all.