My Honda jazz coolent resovoir cap broken. I'm planning to replace just the cap by myself. What damage could cause by broken cap besides overheating ? Do I need to do coolent replace ? Is air could trap and cause problems ?
Replace the cap. If the car hasn't overheated, don't worry about any possibly damage, there shouldn't be any. Check the coolant level. If low, refill with 50/50 premix Honda coolant (the blue stuff). Some Hondas have issues where if you do not use Honda coolant, it will slowly eat the head gasket and cause it to leak, which will cause you an endless array of trying to fix a cooling issue, ultimately only to be fixed by replacing the head gasket. Just better off using Honda coolant in the first place. You don't need to replace the coolant, just top it off if any is missing. You most likely won't have an issue with air being trapped in the system. It should bleed fairly easily.