* Exhaust Manifold Leak: A crack or leak in the exhaust manifold is a prime suspect. Exhaust gases escaping prematurely would cause extreme heat buildup in the area around the EGR valve and its associated piping. This is a common cause of localized overheating in the exhaust system.
* Catalytic Converter Issues: A clogged or failing catalytic converter can restrict exhaust flow, leading to increased backpressure and higher temperatures throughout the exhaust system. This increased backpressure could be the root cause of the melting.
* Blocked Exhaust System: Somewhere downstream of the catalytic converter, there might be a blockage (e.g., a crushed pipe, debris). This will also cause severe backpressure and overheating.
* Improper EGR Valve Installation: While you replaced the EGR valve, ensure it's correctly installed and seated. A slightly loose fit could cause exhaust gas leakage, leading to localized overheating.
* Incorrect EGR Valve Operation: Even with a new EGR valve, if the engine's computer isn't controlling it properly (due to other sensor problems or a PCM issue), you could still have excessive exhaust gas entering the intake system, potentially contributing to the heating problem.
* Head Gasket Failure: While less likely to be the *primary* cause of localized melting, a failing head gasket could allow coolant to enter the combustion chamber, leading to increased exhaust gas temperature. This is usually accompanied by other symptoms like white smoke from the exhaust, low coolant levels, and overheating.
What to do next:
1. Visual Inspection: Carefully examine the entire exhaust system from the manifold to the tailpipe. Look for cracks, leaks, rust, or any signs of blockage. Pay close attention to the manifold and the area around the EGR valve.
2. Backpressure Test: Have a mechanic perform a backpressure test on the exhaust system. This will measure the amount of pressure building up in the exhaust, indicating potential blockages.
3. Check for Coolant Leaks: Inspect for any signs of coolant leaks around the engine, especially around the cylinder head.
4. Diagnostic Scan: Use an OBD-II scanner to check for any trouble codes related to the engine, emissions system, or oxygen sensors. This can help pinpoint other potential contributing issues.
It's crucial to address the root cause of the overheating, not just replace the immediate symptoms. Ignoring it could lead to more significant damage to your engine or exhaust system. A mechanic familiar with Ford Taurus vehicles can provide the most accurate diagnosis and repair.
