The engine did not reach the expected operating temperature within the expected time - classic symptom of a stuck-open thermostat on the flat-six. The DME calculates that coolant should have reached the thermostat's regulating temperature and it has not. Common as thermostats age on the 987.
SYMPTOMS
- Check-engine light
- Slow warm-up / gauge sits low
- Reduced fuel economy
- Heater slow to warm (in winter)
LIKELY CAUSES
- Thermostat stuck open (most common)
- Wrong-temperature thermostat fitted
- Faulty ECT sensor reading low
- Prolonged idling in cold weather
DIAGNOSIS STEPS
- Watch coolant temp reach and hold the regulating temperature (~87 C) in live data
- Feel for uneven warm-up / early lower-hose heating
- Verify the ECT sensor reads accurately
- Replace the thermostat if it opens early / won't close
RELATED PARTS
- Thermostat
- Engine coolant temperature sensor