That makes sense. If it is already running hot, when the engine is shut, the coolant stays in the engine and no longer circulates. Thus, it boils. Now what can cause this. First is the thermostat. You have replaced that so chances are it is fine. Next, the radiator / engine block could be plugged with sludge and corrosion. The radiator is the most common problem with this. Have you had the system flushed? Finally, is the engine running good other than overheating? Have you seen coolant leak from places other than the overflow? If you check the oil, does it appear to have any coolant mixed in with it? And finally, is the coolant in the radiator clean and not contaminated with oil?
Let me know.
Joe
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Saturday, December 5th, 2020 AT 10:10 AM
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