Q: coolant leak overheats only when driving

The external coolant leak you are referring to can be pinpointed by simple pressure testing of the cooling system when the engine is cold. To find the leak that exists in your case, and get the required repair estimated, please request an engine cooling system leak diagnostic and the responding certified mechanic will get this resolved for you. In regard to the overheating, if the coolant level was low that can cause overheating. There are a few other common causes of overheating, namely a faulty thermostat, a plugged radiator, collapsed hoses, and a faulty water pump or drive belt. Certain engine faults, such as a leaking head gasket or poor engine running condition can also cause overheating. If you desire that this problem be diagnosed by a certified Mechanic, dispatched by YourMechanic right to your location, please request an engine overheating diagnostic. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.