TL;DR: All of my coolant leaked rapidly from the system. Refilled with water to test, none leaked out after driving ~5 miles to a safer parking lot.
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Story:
I bought my 2004 Trailblazer LS (4.2L I6) about a month ago. It has 83k miles on it, but I've had some problems ever since. It was shutting off on me, so after research I did the whole replace radiator cap, throttle body clean, reset fuel trim, and one round of seafoam (in fuel only). After all of that, it ran better for a few days and then I got a really rough idle (especially when cold).
When cold:
Immediately after startup and the car in gear, it would idle extremely rough and have loud vibration sounds. No vibration in neutral/reverse/park.
When at running temp:
If I leave the car in park/reverse/drive and idle, it shuts off occasionally. When idling and the AC fan set to 4 or 5, it bogged down and I get the reduced engine power when accelerating from idle. It throws a CEL but it goes away after the 2nd crank and I've yet to catch the code.
Today:
Houston weather, 90ºF+ day, I start driving home from work and the idle is even rougher. This time it's a constant rhythmic pulsing (wub wub wub). After 5 minutes, I get reduced engine power and restart (mid traffic). Start running again. Next I get check gauges, notice temp gauge pegged at 260. I get to the nearest parking lot I can find, park, and hear a "whoosh" sound. All of my coolant dumped out of the car within 5 minutes. Engine bay splattered with green coolant. To test for the leak, we fill it with water and none comes out. Drive it back to my work parking lot, no overheating issues, no leaking. Does not evacuate the water from the system after parking. The car was off for ~30 minutes between overheat and driving back to work. Shouldn't be enough time for significant engine cooling.
I have no idea what happened. What could drain all of the coolant from the system, and then hold all of the water?
------
Story:
I bought my 2004 Trailblazer LS (4.2L I6) about a month ago. It has 83k miles on it, but I've had some problems ever since. It was shutting off on me, so after research I did the whole replace radiator cap, throttle body clean, reset fuel trim, and one round of seafoam (in fuel only). After all of that, it ran better for a few days and then I got a really rough idle (especially when cold).
When cold:
Immediately after startup and the car in gear, it would idle extremely rough and have loud vibration sounds. No vibration in neutral/reverse/park.
When at running temp:
If I leave the car in park/reverse/drive and idle, it shuts off occasionally. When idling and the AC fan set to 4 or 5, it bogged down and I get the reduced engine power when accelerating from idle. It throws a CEL but it goes away after the 2nd crank and I've yet to catch the code.
Today:
Houston weather, 90ºF+ day, I start driving home from work and the idle is even rougher. This time it's a constant rhythmic pulsing (wub wub wub). After 5 minutes, I get reduced engine power and restart (mid traffic). Start running again. Next I get check gauges, notice temp gauge pegged at 260. I get to the nearest parking lot I can find, park, and hear a "whoosh" sound. All of my coolant dumped out of the car within 5 minutes. Engine bay splattered with green coolant. To test for the leak, we fill it with water and none comes out. Drive it back to my work parking lot, no overheating issues, no leaking. Does not evacuate the water from the system after parking. The car was off for ~30 minutes between overheat and driving back to work. Shouldn't be enough time for significant engine cooling.
I have no idea what happened. What could drain all of the coolant from the system, and then hold all of the water?