Auction Fiesta ST with 'Blown Engine' - Sensor Issue or Real Problem?

Auction Car Discovery and Initial Assessment

• 💡 A 2015 Ford Fiesta ST was purchased at auction listed with a "blown engine" and "overheating" issues for $3,200.
• 🔍 The listing's single picture showed the car running with the coolant gauge pegged hot, suggesting a potential sensor issue rather than a catastrophic engine failure, especially given a known recall for similar problems.
• 🎯 The car was described as highly optioned with 100,000 miles and in good condition, with potential resale value of $8,000-$10,000 if the issue was minor.

Investigating the Overheating Issue

• ⚠️ The initial inspection revealed the coolant gauge pegged hot on a cold start, but the coolant level was normal, reinforcing the sensor theory.
• 🕵️‍♂️ Research indicated a potential recall or technical service bulletin related to a coolant temperature sensor or wiring, and a separate recall for a cracked cylinder head due to overheating.
• 🛠️ Upon inspection, a hacked-up electrical connection with foil was found near the coolant temperature sensor, suggesting a non-factory modification.

Sensor Diagnosis and Repair

• 🔬 Two key sensors were tested: the coolant temperature sensor and a cylinder head temperature (CHT) sensor, which was added in April 2015 for overheating detection.
• 📊 Both the original coolant temperature sensor and a suspected CHT sensor showed significant resistance differences compared to new parts, indicating they were likely faulty.
• ✅ Replacing both sensors and clearing codes temporarily resolved the overheating gauge and limp mode, suggesting the issue was sensor-related.

Further Mechanical Work and Testing

• 🔧 The car underwent a comprehensive brake job (front and rear pads and rotors) and fluid changes (engine oil, DCT fluid).
• 🌡️ A lower temperature thermostat (180°F) was installed to help manage the engine's inherent tendency to run hot.
• 🚗 After repairs and fluid services, the Fiesta ST was tested, showing no warning lights and normal coolant temperatures, though a custom jumper harness was needed for the CHT sensor due to a missing port on the cylinder head.

Performance and Modifications

• 🚀 The car was found to be peppy and handled well, with a suspected Stage 2 tune indicated by boost pressure readings up to 34.8 PSI, significantly higher than stock.
• ✨ After a wash and ceramic coating, the Fiesta ST looked nearly new, with an estimated total investment of around $420 for all repairs and upgrades.
• 🤔 The owner considered selling the car but decided to keep it for a while due to its excellent condition and fun driving dynamics.