Another Cooling System Question

[Willis76]

I've looked through many of the threads on cooling questions and have yet another question.

Just what is the purpose of, or theory behind, those plastic expansion / recovery tanks?

When and why does the coolant flow to and from these tanks to the radiator?

Are they under under pressure like the rest of the system or does that (pressure) end at the radiator cap?

Mine has cracked and I am replacing it - along with new coolant, hoses, etc., etc., ........

Thanks

 

[Bob Chadwick]

The cooling system is under pressure. The radiator cap retains either 15 or 16 pounds of pressure before it releases created by the heat of the engine. This raises the boiling point of the coolant up to somewhere in the range of 260 - 265 degrees, which is also the approximate boiling point of oil. Your coolant temp gets this high and the cap releases.

With a properly functioning systen this doesn't happen except under two conditions; extreme operatiing conditions such as a long, steep incline on a hot day and on occasion when you turn your car off. On those occasions when you turn your car off and it gets over the pressure of the cap, the radiator boils over.

The beauty of the overflow tank is that it catches this released coolant and as the car cools off, the coolant is sucked back into the radiator. This allows for a radiator that is always full. Without the overflow bottle, you would loose that little bit that blows off when you turn the car off and would not have a full cooling sytem.

 

[bradfordsvettes]

one other reason for an over flow tank is the fact that the radiator is filled to thre brim with no air in the system there is much less corrosion and oxidation no oxygen no oxidation steve

 

[Willis76]

Thank you both - now I know a little more ....