When I shut the car off the tank boils over and I lose coolant

2002 SATURN SC2
248,000 MILES • 1.9L • 4 CYL • 2WD • AUTOMATIC
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DANNYNASO
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When the coolant tank is full, the car temperature seems to be fine. As soon as I shut the car off the coolant starts to boil in the coolant tank and I lose coolant. Also when idling the temperature tends to go up to a little over half way. No apparent leaks when the car is running except from the coolant after i shut it off. Radiator is about 4 years old, fan is new, water pump is about 6 months old, coolant tank replaced 4 months ago, thermostat is about 11 months old (got another thermostat since it was under warranty, replacement pending). what to do?
Aug 11, 2019 at 6:57 PM
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DANNY L
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Hello, I'm Danny.

Just quick question first. Have you tested the radiator cap? I know it sounds basic but if not holding pressure that would cause boiling over into the overflow tank.Here is a tutorial on how to pressure check.Most auto parts stores have a tool loaner program will rent you one.The tester comes with an adapter to test the radiator cap.

https://www.2carpros.com/articles/radiator-pressure-test

Hope this helps and thanks for using 2CarPros.

Danny-
Aug 11, 2019 at 8:47 PM