Are the electric fans even activating . . . ?!
How many miles?
coolant level correct?
If you’ve got an obvious coolant leak, such as a radiator or water pump, I’d suggest replacing those parts, before getting in too deep. sometimes it’s that easy
You can use a block tester to determine if combustion gases have found their way into the crankcase
Most auto parts stores will have this kit in stock, I believe it’s less than $50. The kit will have instructions, and there should be plenty of youtube videos, as well