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2004 chevy trailblazer_ls
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Discussion Starter #1
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?
 

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2004 chevy trailblazer_ls
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Discussion Starter #4
No OnStar, no SES light. I don't think it's still covered under warranty. I'm going to try to get it home tomorrow and start leak hunting. I don't see it leaking from any hoses, so my theory is that it leaked from the water pump seal. The spray pattern in the engine bay leads me there. Could be a stuck closed thermostat as well. Not sure if I'm way off the mark until I get it home and start poking around.
 

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2004 chevy trailblazer_ls
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When the temp went to 260 you may have just boiled the antifreeze out of the engine.
Find the cause of the overheating and go from there.
You may be able to rent a radiator pressure tester to check for leaks, too. Autozone, Advanced auto rents them I think.
 

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2004 chevy trailblazer_ls
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Discussion Starter #6
It's definitely leaking from somewhere. I got it home with no issues, and no overheating. I left it alone to cool before I started. Started it up this time, and it started pouring out again (temp stayed at 210).




It seems to be coming from the front of the engine towards the driver side. I can't get a good look at the water pump without disassembling a lot of things. I checked all of the hoses and couldn't find a leak. No signs of it coming from the intake manifold.
 

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2004 chevy trailblazer_ls
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Sounds like the water pump.
If you can get a mirror in there, look for a small hole in the bottom of the pump, may be leaking out of there. Also, grab the fan and try to wiggle it, bearings in the water pump could be shot.
PIA job, be careful when re-assembling the shroud that you don't damage the radiator. Also, get an AC Delco pump.
 

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2004 chevy trailblazer_ls
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Discussion Starter #8
New water pump is on the way. I got the better gasket for it as well. Is any additional sealant required with the composite gasket?

Grabbing some new spark plugs while I'm at it. Could the water pump going bad be attributing to the rough idle?
 

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2006 saab 9_7x
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New water pump is on the way. I got the better gasket for it as well. Is any additional sealant required with the composite gasket?

Grabbing some new spark plugs while I'm at it. Could the water pump going bad be attributing to the rough idle?
Make sure you get AC Delco 41-103 Iridium spark plugs. Others don't seem to play well with the 4.2 I6.
 
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