hello
due to an argument in anther forum, i saw that the reserve hose from the radiator is below the pressure cap, so as i get it coolant passes to and from the reserve tank freely, and the cap releases steam to the atmosphere. am i wrong?
some youtube videos show that the cap controlls the passage of coolant itself, others claim that the cap releases only steam to the reserve tank where it condenses back to coolant.
i'm totally confused here.

 

Coolant can not pass freely between the radiator and reserve tank, because the radiator cap is designed to hold pressure on the radiator. Take a look at where the radiator cap seals in the neck of the radiator, because it seals that reserve port.

The radiator cap seals the radiator up to ~15 psi. When the coolant heats up and gets above 15 psi, the radiator cap opens the seal on the reserve line to allow liquid coolant to leave the radiator and enter the reserve tank to relieve pressure to below 15 psi. You may loose some liquid to steam, but I think the reserve tank is cool enough to condense most of the water.

The opposite is true when the radiator cools after you shut off the engine, because the radiator cap opens and allows the radiator to draw in coolant from that reserve tank.

 

On any car, the cap does the job of holding pressure inside the radiator, but releasing a little when it gets too high. Some cars release it as steam, some as liquid, some have an overflow bottle & some have a pressurized bottle with the cap on top of the bottle. Different car companies tend to have their own schemes.

Hondas in particular, the radiator is supposed to be completely full of liquid without any air or vapor space. As the engine heats up, the liquid expands & the cap releases some of that liquid into the hose for the overflow bottle. When you turn the engine off & it cools down, the cap allows that liquid to be easily sucked back into the radiator without sucking air back in and without making much of a vacuum in the system.

There's 3 seals on the cap.
1. The outermost one, largest diameter, seals against the uppermost lip of the radiator neck. That one pretty much stays sealed always.
2. The next one down, smaller diameter, is spring-loaded & seals against a smaller lip a few mm down inside the radiator neck. The overflow hose connects between seals 1 & 2. The spring controls the pressure inside the radiator & allows the expanding liquid into the little hose for the overflow bottle.
3. The smallest seal is a little disk on the underside of seal #2. It's very light spring allows liquid to be sucked back into the radiator as the engine cools down.

So...
Was there a reason for the question? Is yours working like this or is something wrong?

 

thanks for the explanation. mine is ok, now i noticed the small hole for the overflow hose between the 2 lips of the filler neck.

 

Sometimes the little hose to the overflow tank gets hard & cracks, allowing air to suck back instead of liquid while the engine cool off. Just something to check at the age of that car...