If your Honda Acty is running hot or the temperature gauge is spiking, it’s critical to diagnose the issue quickly to avoid serious engine damage. Overheating is most commonly caused by low coolant, air pockets in the system (especially after a coolant change), a stuck thermostat, or a failing radiator fan. Start by checking the coolant level in both the radiator and overflow tank (only when the engine is cold), and look for leaks around hoses, the radiator, or the water pump. If the coolant is full but bubbling or not circulating, the thermostat might be stuck closed, or there may be trapped air—a common issue if the system wasn’t properly bled. On fuel-injected HA6/HA7 models, make sure the electric radiator fan turns on when the engine gets hot; if it doesn’t, check the fan switch, relay, and fuse. In carbureted HA3/HA4 models, a failing mechanical water pump could be to blame. Also inspect the radiator cap—if it can’t hold pressure, it can cause overheating even if everything else is working. Diagnosing overheating early can save your head gasket, so always address it at the first sign of trouble.