How is it possible to lose coolant, if the coolant system in a car is a closed loop,
 

I have confusion as to why people need to top off their coolants from time to time. How is that a phenomenon if the cooling system is supposed to be a closed loop? I understand that if there were leaks, then losing coolant is apparent, but if there are no leaks, how is it possible? I thought that if it was a closed loop, you should not lose a single drop of coolant.


Edit #1: The title got cut off for some reason, but the entire title is: How is it possible to lose coolant, if the coolant system in a car is a closed loop, and there are no leaks?

It leaks or burns. This is your second coolant thread. Are you loosing coolant? If so, how much and how often? I asked this in the other thread but you didn’t answer.

Your statement can only be accurate if you assume it is a closed loop.

In reality, it is not a closed loop.

You can seep moisture via any of the gaskets, bad seal, head gaskets. You also have a radiator cap that vents excess pressure if the temps are too high, which means you have coolant that has escaped a "closed loop"

-alex

@ermax Did you read my question in it's entirety? "...if there are no leaks, how is it possible?" Also, See my latest post on the previous thread.
@mav1178 Those things you mentioned, "gaskets, bad seal, head gaskets, etc." are all about problems associated to abnormal damage? I'm wondering about if the coolant system is designed without any issues. Is the coolant system designed to be closed entirely, is what I'm asking, and why there are any losses if there are no leaks.

How is it possible to lose coolant, if the coolant system in a car is a closed loop,
 

No it isn’t closed entirely. The cap is designed to put pressure on the system which raises the boiling point. But it is also designed to bleed off if the temp goes too high. Other than that it’s closed.

I’ve never owned a car that didn’t consume a little. You still haven’t given a clear answer on how much and how often you are putting coolant in.

Edit: Mav already addressed this. Sorry.

You can lose coolant if you boil over via the radiator cap, but not all of the boiled over liquids make it back into the radiator after the engine cools down.

Over time this ends up in the overflow tank.

90% of the time a car overheats because the radiator cap has gone bad.

To answer your question, if the coolant system is design and is really made to be closed entirely (and I mean perfectly sealed), you will not have any coolant loss.

But as others have said, no modern car have a sealed closed coolant system. The twins have coolant loop that allows venting to prevent pressure buildup and for coolant to flow in case it boils. Coolant evaporates when it comes in contact with engine block and that evaporated coolants builds pressure. Now the pressure will travel from high pressure to low pressure point (outside the coolant loop) as there is no venturi effect happening and hence the air will try and find its way out. And this air pressure sometimes also pushes coolant into the overflow tank.

overflow tank has vent hole in it. Coolant evaporates out vent hole


https://mishimoto.com/engineering/wp...de-by-side.jpg

thanks bro, it's bothered me for months till i foud this vent hole.

Yep - its not really a sealed system. The coolant is somewhat close to boiling, so it wants to evaporate - there are a few opportunities for evaporation and slight leakage over time. You shouldn't be losing much coolant though. It should be a very minimal loss.

As others have said, the overflow tank isn't 100% sealed for a reason, and on the Twins, is about a foot away from a quite toasty catalytic converter, which would tend to encourage the water to evaporate out of the coolant. Most cars don't have the overflow tank so close to the hot exhaust components, so they typically do better in this regard.

Steve99 is right on. The coolant expands and flows into the overflow tank. It is hot and evaporates (at a slow rate),
I too am still waiting for an answer to how much how often is lost from OP.

Wait. You don't buy a gallon of coolant with every 5 quarts of oil and a filter?

Food for though

https://motocrossactionmag.com/ten-t...rless-coolant/