02 Trailblazer, 4.2L 6 cylinder.
I'll keep this simple - the thermostat stuck shut causing the exhaust manifold to overheat so it cracked. This also brought with it a sound that sounded like an exhaust leak, which the local mechanic agreed with.
All parts that have been replaced since that event include the thermostat, fan clutch, exhaust manifold (including new gasket and donut seal), upstream O2 sensor, and VVT control solenoid (oil in the plug, only noticed it was bad because I pulled the plug in the process of getting the manifold out).
The thermostat was replaced before the manifold and we did a coolant flush at this point, BEFORE replacing the manifold. This seemed to affect the noise being made while the engine was running as it became noticeably quieter.
That said, even now with the manifold replaced we still have a sound that on its face seems to be an exhaust leak, but I've learned with this vehicle there can be about 50 different causes for the same problem. The noise can be heard any time the engine is running. It seems to come from the area around the exhaust manifold, or at least that side of the engine as it is not as loud on the other side. It can be heard from within the vehicle.
The sound is somewhat indistinct and hard to describe, it's like an on/off ticking sort of sound, but I'd hesitate to describe it as metallic. Any ideas? Does it still have a leak or maybe something else is going on like a bad lifter?
I'll keep this simple - the thermostat stuck shut causing the exhaust manifold to overheat so it cracked. This also brought with it a sound that sounded like an exhaust leak, which the local mechanic agreed with.
All parts that have been replaced since that event include the thermostat, fan clutch, exhaust manifold (including new gasket and donut seal), upstream O2 sensor, and VVT control solenoid (oil in the plug, only noticed it was bad because I pulled the plug in the process of getting the manifold out).
The thermostat was replaced before the manifold and we did a coolant flush at this point, BEFORE replacing the manifold. This seemed to affect the noise being made while the engine was running as it became noticeably quieter.
That said, even now with the manifold replaced we still have a sound that on its face seems to be an exhaust leak, but I've learned with this vehicle there can be about 50 different causes for the same problem. The noise can be heard any time the engine is running. It seems to come from the area around the exhaust manifold, or at least that side of the engine as it is not as loud on the other side. It can be heard from within the vehicle.
The sound is somewhat indistinct and hard to describe, it's like an on/off ticking sort of sound, but I'd hesitate to describe it as metallic. Any ideas? Does it still have a leak or maybe something else is going on like a bad lifter?