First thing to check is if there’s a thermostat in. It may be running at normal temperature if some cowboy took the stat out. Also, I’d try a reverse flush where you’ll pump the water through the bottom hose. Depending on where you are based (not in Siberia for example) you can leave a very weak mix of coolant in for a couple of days and then check for leaks before you commit to refilling with a proper solution.
Don’t forget to check your manual for the right specification for the coolant. I had to supply my own for my flush and replenish.
