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Discussion Starter #1
About to do a coolant flush on my 04, 3800 Series II. Anyone know where the engine coolant drain is located? I’ve heard a couple different things from different sources. Some say it’s the same threaded holes as the knock sensors, some say theres a drain plug above the oil pan, and some say there flat out aren’t any. don’t particularly feel like laying under the car for hours scratching my head wondering where the hell it is, taking things apart that don’t need to be.
 

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About to do a coolant flush on my 04, 3800 Series II. Anyone know where the engine coolant drain is located? I’ve heard a couple different things from different sources. Some say it’s the same threaded holes as the knock sensors, some say theres a drain plug above the oil pan, and some say there flat out aren’t any. don’t particularly feel like laying under the car for hours scratching my head wondering where the hell it is, taking things apart that don’t need to be.
Bottom, right (passenger) side of the radiator.
 

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The radiator drain petcock? On the drivers side bottom of the radiator? I am talking about draining the coolant from the block itself, just want to clarify.
 

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The radiator drain petcock? On the drivers side bottom of the radiator? I am talking about draining the coolant from the block itself, just want to clarify.

I misunderstood you - I thought when you said the engine coolant drain, you were referring to the radiator peacock.

Although I have owned W-body models with the 3.8 V-6 (one was a 2004 Grand Prix GT2 with the 3.8 Series II engine), I cannot help you with the engine block drain plug locations. I have heard horror stories from some about having problems when trying to remove the plugs with the engine installed in the vehicle.

Some GM vehicles have “freeze plugs” - which are caps that are pushed into the block casting opening. The only way to remove them is to use a punch and drive tool to “knock” the plug partially out of the opening (then pull it out of the block with a pliers) - then install a new plug which is pushed-in.

Some GM vehicles have brass-threaded engine block drain plugs (some of the LS series engines). Although easier to remove (if you have access) - they are prone to thread-stripping.

Is there any reason that you want to remove the plugs to drain the engine block? Repeated flushings using distilled water, circulated through a warm engine, then drained via the radiator petcock will get most of the coolant out of the engine block.
 

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^+1. Then remember to strengthen your 50/50 mix initially with concentrate to compensate for the h2o left in the block.
 

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The plug on my 2003 is in the front, to the right of the oil filter, about 3/4 inch hex, tight fit, but easy to reach. Pretty sure there's one in the rear but I couldn't see it.
 
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