does the radiator actually take coolant from the reservoir? or does the coolant only go there when the radiator is over filled?

how does it work?

 

The tank takes up the slack when the system builds more pressure than the pressure cap can hold due to heat.
As the cooling system cools, the pressure on the inside of the cooling system becomes less than the pressure on the outside (atmosphere) which results in coolant being pushed back in the system until there is an equilibrium.

Some would say that it is sucked back in, but it's really the act of positive pressure.

 

so if you were low on coolant...

and you let your car cool down...

the next time you warm it up, it should have pulled more coolant into the raditor and topped it off?? is this right?>

 

As long as there are no leaks within the cooling system, yes.

 

Um.. I mean no.. I didn't read your question well enough.

If the system was low to begin with, then you will only refill the system to the point that it was at before you heated and cooled the system.

 

Ok.. I think that I better sit back on this one and say, that I am not 100% sure.
Because we are talking about two functions, expanding gas, and an expanding fluid, I am not sure where one becomes a greater force and if there is enough energy stored from the whole process to fill the system beyound the orignial starting point.

It's a good question. One which I think that I have to say I am not qualified to answer. So never mind what ever I have said.

 

hmm... heres a simplified version (i hope this is easier to understand)


say your running a bit low on coolant (and you dont have any leaks)... can you top it off through the reservoir, or can you only top it off by directly adding to the radiator?

 

^bump^

 

The resevoir will act as a surge volume when the radiator heats up and expands forcing coolant out and into the resevoir. When the radiator cools down and the coolant contracts it will form a small vacuum in the radiator and force the coolant in the resevoir to go into the radiator and equalize the pressure. It's kind of like a siphoning effect and you have to make sure that the radiator if topped off and the resevoir is full or it will just suck in air to equalize and leave you with an air pocket. Gases are a lot more compressable than liquids so you need to keep up with your radiator fluid at all time. Hope this helps.