What causes antifreeze to run out of the overflow tank after the car is shut off and when the cap is removed the tank seems low, then antifreeze runs out?

pressure causes the coolant to go into the overflow, as the engine cools it siphons back to the radiator. if the tank keeps running low you must have a leak some where

Its normal for the car to have antifreeze going to the overflow tank if thats what your asking.

Stop me if this has NOTHING to do with your problem (or if it's already been solved)...I don't know a lot about cars so...My Ford Taurus kept overflowing antifreeze from the reservoir cap. Car started to over heat and kept spilling"/dumping" antifreeze every time I turned the car off. The antifreeze reservoir had been replaced less than a year prior, and water pump, radiator, etc looked at. I got a free estimate that stated my water pump was NOT the issue, but I did need a new radiator and my reservoir tank needed to be replaced (again)....$800 parts and labor.... However...I noticed the overflow holes on the tank, and also that the orange liquid (antifreeze), was also spilled around the cap lid. I also noticed the CAP on the antifreeze reservoir would loosen when tightened completely- hence, not sealing correctly. So I went to the dealer, bought a new reservoir cap for $15, replaced it, and never had an issue after! I also found out that the CAP was a DEALER PART ONLY, and when the tank itself was replaced, the CAP was the OLD one! Problem fixed! Maybe it's similar? Or something "more serious".

your antifreeze is low that means you have to fill the radiator and the overflow bottle.the reason the gauge fluctuates is that you have air in the system.with the radiator cap removed,start the car turn the heater on high and let the engine run till the thermostat opens.you will know this as the level of antifreeze will fall,fill the radiator and replace the cap turn off the engine and heater and fill the over flow bottle. you may have a bleeder on the top of the engine around the themostat, but if you dont no worry cause your problem should be solved.

COOLANT-ADDING ADDITIONAL
Do not remove radiator cap to add coolant to system. When adding coolant to maintain correct level, do so at coolant reserve/overflow tank. Use a 50/50 mixture of ethylene glycol antifreeze containing Alugard 340-2 y and low mineral content water.
Remove radiator cap only for testing or when refilling system after service. Removing cap unnecessarily can cause loss of coolant and allow air to enter system, which produces corrosion.

COOLANT LEVEL CHECK
The cooling system is closed and designed to maintain coolant level to top of radiator.
WARNING: DO NOT OPEN RADIATOR DRAINCOCK WITH ENGINE RUNNING OR WHILE ENGINE IS HOT AND COOLING SYSTEM IS UNDER PRESSURE.
Remove radiator cap. The coolant level should be to top of radiator. If not, and if coolant level in coolant recovery bottle is at ADD mark, check for:

• An air leak in coolant reserve/overflow tank or its hose
• An air leak in radiator filler neck
• Leak in pressure cap seal to radiator filler neck

TRANSMISSION and OIL LEVEL CHECK TUBES


I’m happy to help further over the phone at https://www.6ya.com/expert/jeremy_69f3cc28d95bf514

I would check for visible cracks and leaking at the overflow tank when the engine is cold, then when the engine is running and at operating temperature and not running and at operating temperature as well as during cool down. Also check the coolant overflow hose for leaks or obstructions inside the hose or if the hose is kinked. Check to make sure that the overflow tank cap is damage free and securely fastened.

Until you get it figured out use regular water. Replace thermostat and radiator/coolant tank caps. Thermostat regulates pressure in the motor and allows radiator to cool. Caps regulate atmosperic pressure. Either or both being bad will cause you system to siphon and fail.

The first thing to check is the coolant (antifreeze) level in your radiator. If this level is too low it could cause your heater not to blow hot air. Check this when the engine is cold by removing the radiator cap. Do not remove the radiator cap when the engine is hot. If you do, you run the risk of getting scalded by hot water and steam that can shoot out the top of the radiator. The radiator should be completely full. If it's not, fill it up with a 50/50 solution of antifreeze and water. Also make sure the radiator overflow tank is filled up to the full mark. This is usually about halfway up the tank.
If your coolant level is ok I suspect you may need to replace the thermostat. It may be sticking shut and not letting hot water get to your heater core, or it may be sticking open and preventing your engine from reaching its normal hot operating temperature. A thermostat is relatively inexpensive and usually easy to replace. Just make sure you follow the instructions and put it in facing the right direction. If the thermostat is ok then you may have a blockage in your heater core. Replacing a heater core can be a difficult job on some car. If this is your problem I recommend taking the car into a garage to have the repair done. I hope this helps you out.

antifreeze/coolant is low. with car off and engine cool remove overflow cap and fill to cool level. 50/50 mix or premixed is okay. overflow tank is clear or yellow located against firewall .

i had the same problem until i changed my water pump,so you might want to get that checked out