Overheating

We need to start with filling the system and pressure check it for leaks. Start with external leaks and repair any that we find. If there are no external leaks and it holds pressure of about 18 PSI for at least a couple hours, then we need to remove and check the thermostat.

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

https://www.2carpros.com/articles/engine-overheating-or-running-hot

https://www.2carpros.com/articles/how-an-engine-thermostat-works

You need to remove the thermostat and put it in boiling water and make sure it opens.

Next let the engine run and start to get hot and make sure the fan comes on.

Let me know the results of all this and we can go from there but the next step is to check the head gaskets.

Here is a guide that talks about this:

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

The first thing would be to determine where the coolant went to make it low. I would fill it with plain water and start testing for leaks first. No reason to start replacing a water pump or radiator core if it has already blown a head gasket when it got hot. Take a look at this guide and try a few of these tests first to determine if it has deeper problems:

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