Radiator Overflow Bottle

[SimonTuffGuy]

How is the overflow bottle SUPPOSED to work?

I'm not sure that mine is working properly... I thought that water was to go in the bottle as it got hot, and then as it needed, would draw it back out.

Mine just seems to be pushing it out and then it's dripping on the ground. The radiator is no longer full, nor is the overflow bottle.

[festivaWES]

When it gets hot and there is boil-over it goes to the reserve tank...draws it back out when it is needed. You have the concept.....why yours is drawing it out but the radiator isn't even full is probably because you coolant system isn't pressurizing (sp).

[FestYboy]

no, that's a sign of a bad presure cap. replace the cap.

[festivaWES]

doesn't a cap pressureize the cooling system?

[joebreck117]

I THINK this is how it goes...you have your pressure cap, which fits comfortably snug into the radiator neck. the cap is essentially two pieces held together by a spring. when the cooling system overheats, there is a certain amount of pressure created which pushes the bottom portion of the cap up. once it rises high enough, the excess pressure is released through the overflow tube into the reservior. when the pressure goes down, the cap goes back down.
not all caps are the same, however, they are rated by how much pressure is needed to make the spring holding the cap together compress. or you can say they differ by spring constants.

Once again, I THINK that's how it goes. feel free to correct me, I may have been thinking the wrong thing all along. Also, sorry if it's hard to understand, I don't always word things very well

[Damkid]

I THINK this is how it goes...you have your pressure cap, which fits comfortably snug into the radiator neck. the cap is essentially two pieces held together by a spring. when the cooling system overheats, there is a certain amount of pressure created which pushes the bottom portion of the cap up. once it rises high enough, the excess pressure is released through the overflow tube into the reservior. when the pressure goes down, the cap goes back down.
not all caps are the same, however, they are rated by how much pressure is needed to make the spring holding the cap together compress. or you can say they differ by spring constants.

Once again, I THINK that's how it goes. feel free to correct me, I may have been thinking the wrong thing all along. Also, sorry if it's hard to understand, I don't always word things very well

I think your right

[FB71]

You're all pretty close, and FestYboy has the correct diagnosis.

A radiator cap has two 'valves' in it, comprised of the rubber gaskets, metal backing discs and springs. As engine temp normally increases, the coolant expands. At a pressure determined by the spring on the relief valve in the cap, the valve will open, and allow excess coolant to flow to the bottle. As the engine cools (after shutoff), the coolant contracts, and generates negative pressure in the system. This causes the siphon valve in the cap to open, sucking the excess coolant back into the radiator.

Simon, the siphon vlave in your cap is shot, which is why the bottle overfills and drains the radiator. Replace the cap.

[mechanicaldj]

the cap works :

when the system exceeds the rated cap pressure due to normal coolant temps and expansion of the coolant
the cap will release some pressure.

when the engine cools, the coolant will contract and will create a vacuum in the system and the cap will draw the fluid back in

[SimonTuffGuy]

Thanks all... I'll grab a new cap and see how that works.