Block coolant drain plug?

[dhanger]

Does the 4.2L have a drain plug for the coolant in the block? According to the manual it does, it's mentioned after step 8 of the draining procedure:

Cooling System Draining and Filling (Static Fill) — 2008 Chevrolet TrailBlazer 2WD L6-4.2L Service Manual ~ LEMON Manuals

Repair manual for the 2008 Chevrolet TrailBlazer 2WD L6-4.2L, including electrical diagrams, bolt torques, and labor times.

lemon-manuals.la

I can't see any plug that might be for coolant and Google gives me nothing about it. I'd like to completely drain the coolant for a flush--just using the lower radiator hose drains about 6.5 quarts and the spec is for 9.7 quarts so there's still about 3 quarts remaining.

 

[movietvet]

Typically a "drain plug" on the block, will have either a square head or a 6 point head and will be located on either side of the block and may even be hidden behind a motor mount. Should have a pipe thread too. May even have a sunken allen head hole.

 

[dhanger]

Yeah I looked for all the signs and I just recently changed motor mounts so I've been all over the lower block area on both sides. I'm beginning to think the manual is wrong, especially since I can't find any info about it anywhere.

 

[movietvet]

I would bet there is a block plug somewhere. It may be at the back or front, too. Just a guess.

 

[budwich]

I suspect there is no drain plug. I believe there are frost plugs (which could be punched out and replaced there after) but most people doing a "complete flush" just do multiple water flushes and then follow up with a "calculated concentrate fill" there after.

 

[Mooseman]

I have to agree. I have never seen a coolant drain plug on these. Google AI seems to agree:

The 4.2L GM Atlas engine (LL8) does not have a dedicated, accessible engine block coolant drain plug. To drain the cooling system, you have to use the drain valve (petcock) on the bottom corner of the radiator or detach the lower radiator hose. [1, 2, 3, 4, 5]


The lack of an engine block drain plug means a standard radiator drain won't empty the entire system. Because a significant amount of coolant stays trapped inside the block, DIYers and mechanics often use specific techniques to ensure a complete flush. [6]
Best Practices for Draining the System

• Use the Radiator Petcock: Locate the drain valve at the bottom of the radiator to let out most of the fluid.
• Remove the Lower Radiator Hose: For a faster or more complete drain of the radiator, squeeze the hose clamp and pull the lower hose off.
• Flush the Block: If you are changing coolant types (e.g., from an unknown fluid back to manufacturer-recommended Dex-Cool), disconnect the heater core hoses and flush the block with a garden hose to push out the trapped old coolant. [6, 9, 10, 11]

If you are doing a coolant flush, let me know:Is your Atlas engine currently overheating?Are you switching to a different coolant type?I can provide step-by-step instructions for a full system flush and refill without trapping air in the engine.
AI can make mistakes, so double-check responses
[1] https://www.trailvoy.com/threads/4-2-i6-envoy-cooling-system-flush.53430/
[2] https://www.trailvoy.com/threads/4-2-i6-envoy-cooling-system-flush.53430/
[3] https://www.carcarekiosk.com/video/2008_Chevrolet_Trailblazer_4.2L_6_Cyl./coolant_antifreeze/flush_coolant
[4] https://www.youtube.com/watch?v=kSlwU-RVWmU
[5]

[6] https://www.youtube.com/watch?v=Hy6DB71Ab90
[7] https://www.youtube.com/shorts/myZiEo5-9ZE
[8] https://www.youtube.com/watch?v=k2Uk8fqadM0
[9] https://www.youtube.com/watch?v=TVifd5BzTgs
[10] https://www.youtube.com/watch?v=Hy6DB71Ab90
[11] https://www.youtube.com/shorts/VpRF5GsBpCI

 

[budwich]

I see from the "old site" this post.... quote:
"I installed my Goodwrench Block Heater on my 2002 Envoy with the front driver side jacked up and the wheel removed. I installed it through the wheelwell in about 40 minutes from start to finish. Was one of the easier jobs Ive done on T360's over the years!!

For the record, the 'frost plug' is threaded. Dont need to knock anything out. I took out the plug, and quickly threaded in the block heater, thus only draining about 1.5 quarts of dex-cool. I refilled, started up, checked for leaks, and have been using my block heater for 3+ years now!"

So there appears to be a drain plug on the driver's side.

 

[movietvet]

I had no idea what it looked like or where it was but I was pretty sure it had a threaded drain plug.

Plus, the ones I remember are at least on the d/s, if not on both sides.

 

[dhanger]

Huh, well I gave up on it and finished the task shortly after posting. I had decided to change the thermostat at the time and discovered that it was possible to remove the thermostat from the housing. After re-installing the housing I could freeflow the coolant system a couple of times with distilled water to get a good flush, put the new thermostat in, and re-filled with Dexcool. By two different methods I determined that the remaining coolant that didn't drain was almost exactly 3 quarts, which means that even if I had found the drain plug it still wouldn't have drained completely based on the post about the block heater. Since the manual says that the coolant system capacity is 9.7 quarts I put in 4.8 quarts of concentrated Dexcool then finished topping it off with distilled water to end up with a 50/50 mix.

 

[marcie_chapman38]

Multiple flushes work fine—just bleed any air each time you refill or you'll trap pockets that'll mess with your cooling.

 

[movietvet]

Unless you have a vacuum operated refill set up for the coolant refill, I tend to elevate the side or front of the vehicle a little and refill very slowly with coolant. I don't start the engine till I get the refill level to stop "burping" when filled to the line. This way of doing a refill has always worked for me. Of course, road test and check/refill numerous times.