Can engine run with bad freeze plug?

Yes, an engine can run with a bad freeze plug, but it may lead to significant problems. A bad freeze plug can cause coolant leaks, which can result in overheating and potential engine damage. If the coolant level drops too low, it can compromise the engine's ability to cool effectively, leading to severe issues such as warping or cracking. It's advisable to address a faulty freeze plug promptly to prevent further damage.