Coolant Tank- not stupid, just ignorant about some things

[jb92563]

I have had the overflow on parking issue.
Cause was that I overfilled the coolant level and so out came the extra as I was parking. Problem has never recurred.

The pressure valve next to the fill cap allows the expanding when hot coolant to expand into the coolant reservoir thereby expelling any air that might be in the system.

These expansion pressure valves have been known to leak as the seals get older and the leakage goes down the overflow tube by the right rear tire.
You will see moisture only on the trunk lid above the Cap area if either the Cap or the Pressure valve are leaking, also a crusty residue will form around the pressure valve.

The Coolant Caps have also been redesigned so you want the latest version.

If you don't see any overheating issues and the puddle is by the rear right tire, I would suspect the Pressure valve or the coolant cap.

The coolant cap is very easy to screw down incorrectly and leave a gap so very carefully re-secure it making sure it looks perfectly parallel to the opening.

A coolant tank leak would leak when the tank gets pressurized and forces the crack open and the coolant will end up in your trunk in that scenario.

Just because the engine is warm does not always mean the tank is pressurized as the expansion valve seems to be the gateway to the coolant tank and is not always open.

Hope that helps.

[RBrummer]

Thanks for the info
Cap is new and just replaced the valve
Will keep looking
I had the same massive coolant dump under the right rear due to a loose cap.
Still do not understand why it waited to leak with a bad cap until I parked the car

[mikefocke]

Doesn't water expand when it cools? How long after you stop is the "dump"?

[BrandonJames89]

"Most liquids have a quite simple behavior when they are cooled (at a fixed pressure): they shrink. The liquid contracts as it is cooled; because the molecules are moving slower they are less able to overcome the attractive intermolecular forces drawing them closer to each other. Then the freezing temperature is reached, and the substance solidifies, which causes it to contract some more because crystalline solids are usually tightly packed.

Water is one of the few exceptions to this behavior. When liquid water is cooled, it contracts like one would expect until a temperature of approximately 4 degrees Celsius is reached. After that, it expands slightly until it reaches the freezing point, and then when it freezes it expands by approximately 9%."

Looks like the water/coolant level should go down as it cools unless it is near freezing outside but then antifreeze probably affects this behavior.

I was curious when you asked if water expands as it cools so I did a little research. I knew that it contracted when it cooled and expanded when freezing because of the crystalline structure of the molecules but didn't know what at what point the cooling water started to expand.