How to Troubleshoot Overheating Issues in a 2008 Ford Edge with a 3.5-Liter Engine?

To address the overheating issue with your 2008 Ford Edge, it's essential to start by checking the water flow inside the radiator. This can help determine if the water pump is functioning correctly. When the engine is cold, remove the radiator cap and start the engine. If the water inside the radiator is flowing, the water pump is likely fine. If it’s standing still, that could indicate a defective water pump. Given the fault codes you've mentioned, specifically `P01285` and `P01299`, these suggest that the cylinder head temperature sensor may be shorted or defective and should be replaced. The `P0480` code points to a potential issue with the fan relay, which may also need replacement. If the engine overheats, it can enter fail-safe mode, which typically causes the engine to shut down to prevent damage. However, if the temperature sensors are malfunctioning, the engine might not shut off as expected. Your mechanic's test for exhaust gases in the coolant is crucial, as the presence of exhaust gases could indicate a blown head gasket. However, since you mentioned that the engine oil looks good and there are no signs of a milkshake consistency, it suggests that the gaskets are likely still intact. It’s wise to address the fault codes first and replace the faulty components. After making these repairs, monitor the situation to see if the overheating persists. If the head gaskets were indeed blown, you would typically see oil and coolant mixing, which you’re not experiencing. Since your mechanic has a reliable analyzer, he can reset the fault codes and run further tests. If the codes return, it indicates that the parts need replacing. Starting with the fan relay seems like a sensible approach, especially since it was the first code triggered. This could very well be the root of your overheating problem.