Q: Q: 2007 Infiniti fx35 starts runs fine in park or idle. Overheats when driving, cools in park/neutral. Oil/coolant fine, not milky

There are tests for exhaust gases in the coolant so the head gasket can be ruled in or out. A faulty thermostat can cause overheating so, yes, that is a possibility. The cooling system can’t be ruled out because certain cooling system faults only manifest themselves when there is a load on the engine. Collapsed hoses, once underway, are a possibility. Other common causes of overheating include low coolant level (including that due to leaks), a plugged radiator, a faulty radiator pressure cap, and a faulty water pump or drive belt. Certain engine faults, such as poor engine running condition (lean operation) or exhaust blockages can also cause overheating. An important thing to keep in mind is once an engine has overheated, you should replace your engine cooling thermostat because episodes of overheating can damage the thermostat. If the thermostat is damaged, and left in place, that can set the stage for future cooling system problems. If you desire that this overheating problem be diagnosed by a certified Mechanic, dispatched by YourMechanic right to your location, please request an engine overheating diagnostic and the responding certified mechanic will get this resolved for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.