GAC Toyota Camry: High Engine Coolant Temperature
2026-04-02
Background
Vehicle Model: 2008 Toyota Camry
Fault Symptom
While driving on the highway at 120 km/h, the owner of this 2008 Toyota Camry suddenly noticed rising cabin temperature and sluggish power output. The coolant temperature gauge needle rose all the way to the red warning zone. The driver immediately pulled over onto the emergency lane and opened the engine hood. A bubbling boiling sound came from the engine, and the coolant expansion tank was severely low on fluid.
Fault Analysis
The customer reported abnormal coolant loss starting at the 25,000 km maintenance interval, requiring coolant top-up roughly once a month.
After fully refilling the expansion tank with antifreeze and running the engine for around 30 minutes, the coolant level dropped by 2 cm. The engine oil level measured 1 cm above the maximum mark on the dipstick. The temperature gauge crossed the red line after driving just 10 km, while the engine ran smoothly without shaking and maintained stable idle speed.
Potential root causes were narrowed down as follows:
Cylinder block failure, faulty water pump, leaking upper/lower radiator hoses, leaking heater hoses and heater core, defective radiator, malfunctioning radiator cooling fan, faulty radiator cap, leaking engine core plugs, defective engine drain cock, blown cooling fan fuse, faulty coolant temperature sensor, or short circuits / damaged connectors in the cooling fan wiring harness.
Troubleshooting Procedure
Diagnostic steps performed:
- Inspect engine radiator for leaks – No abnormalities
- Test engine cooling fan operation – No abnormalities
- Check cooling fan fuses for burnout – No abnormalities
- Inspect cooling fan wiring for short circuits – No abnormalities
- Test radiator cap for leakage – No abnormalities
- Inspect upper and lower radiator hoses for repair marks or seepage – No abnormalities
- Inspect heater hoses – No abnormalities
- Inspect engine core plugs – No abnormalities
- Inspect engine drain valve – No abnormalities
- Inspect water pump for coolant seepage – No abnormalities
- Test coolant temperature sensor – No abnormalities
- Remove thermostat and conduct boiling water functional test – No abnormalities
- Check engine exterior for collision damage – No abnormalities
- Disassemble cylinder head and inspect cylinder block – No abnormalities
To pinpoint the exact leakage point, technicians sealed the water passages of the cylinder head and cylinder block with asbestos gaskets, then filled the cooling system with soapy water for a pressure leak test (see Figure 1 & Figure 2). Bubbles surfaced on the right side of the core plug located midway along the cylinder head bolts (see Figure 3 & Figure 4).
The root cause was identified as substandard cylinder head casting, which caused a crack in the internal cooling water passage under high system pressure. This crack allowed coolant to leak into the engine crankcase and mix with engine oil, resulting in severe engine overheating under high-speed driving conditions.
Figure1 pressure leak test
Figure 2 pressure leak test
Figure 3 Leak Location
Figure 4 Leak Location
Replace the cylinder head and conduct a road test; the fault is eliminated.
