Hi,
Oftentimes, the upper hose not being pressurized is due to a faulty radiator cap or in this case, a coolant recovery tank cap. When the system is pressurized, it increases the boiling point of the coolant and helps with circulation. If you haven't checked that, start there.
Next, if that checks good, I recommend getting a cooling system pressure tester to see if the system can hold pressure. If it does, I would simply flush the cooling system and replace the thermostat. If it doesn't hold pressure, then we need to locate a leak. Here is a link explaining how to pressure test it. You will need a pressure tester, but most parts stores will lend one to you.
https://www.2carpros.com/articles/radiator-pressure-test
Let me know your thoughts and if you have other questions.
Take care,
joe
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Monday, November 11th, 2024 AT 7:33 PM