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Q: My car is spitting coolant from the overflow tank

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2004 Chevy Tracker started spitting coolant from the overflow tank. No overheating problems or leaks beforehand until now.

Without any warning, most of the coolant had blown out of the overflow tank. After allowing it to cool for a couple of hours, I refilled the radiator and overflow tank to recommended levels. Drove it another ~6 miles and it started overheating again. Opened the hood and found the overflow tank FULL and spitting coolant again.

The system appears leak free but obviously something ain't right given the symptoms. The coolant system was replaced four years ago after a collision with a deer and everything has worked perfectly since then. This just started today for no apparent reason. What's up with that?

My car has 160000 miles.

A: Hi and thanks for contacting YourMechanic. ...

Hi and thanks for contacting YourMechanic. Check the coolant strength to see what the protection is. A good protection will read 164 degrees Fahrenheit. Check the radiator cap to see if the seal is torn or if the release valve inside the cap has failed or is sticking open. A radiator cap can cause the system to boil and spit out all of the coolant.

If you have good coolant and the radiator cap is new, then the thermostat could be sticking causing your coolant to heat up too much which in turn causes the system to boil. To check if the thermostat is working, start up the vehicle when it is cold and watch the coolant temperature gauge. When the thermostat opens, the gauge will drop a little.

If the gauge does not show this, then, when the upper radiator hose gets hot, right after the thermostat opens, the coolant flows through the hose and you would be able to feel this. Plus, the hose will begin to get cooler as the coolant travels through the hose. If the thermostat was replaced and you still have a boiling issue, then the head gasket has burned on the engine.

If you need assistance, then seek out a professional mechanic, such as one from YourMechanic, to help determine why the car is overheating and why the coolant is boiling out.

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