Loses a gallon every 2-3 days?

Hello,

That is a significant amount of coolant loss. Usually this much coolant loss means a leak somewhere in the system.

Are you seeing any smoke out of the tailpipe?
Typically, when you have coolant mixes with oil it will create white smoke out of the exhaust.

https://www.2carpros.com/articles/white-smoke-or-steam-coming-from-the-exhaust-pipe

White smoke is a sign of a blown head gasket.
Also, when coolant mixes with oil it changes to a milky color.
Do a head gasket test, to see if it is blown. This test uses a chemical, which changes color when come in contact with combustion gases.

Here is a helpful article:

https://www.2carpros.com/articles/head-gasket-blown-test

I have attached diagrams for your reference.

Please let me know of any questions.
Thank you.