Flushing out stop leak

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Just finished up a head gasket job on my 2006 Subaru Outback. It's had lots of years of the official Subaru "coolant conditioner" (aka Holts Radweld). I noticed a decent amount of gunk inside the coolant jacket and head that I'd like to flush out, now that the car is back together.

Any recommendations?

A youtube video recommend Irontite ThoroFlush for cleaning out stop leak. The MSDS lists sodium carbonate as an active ingredient, and I believe TSP has been used too.

Pictures of the block:
https://lh3.googleusercontent.com/c38GMv...w=w1385-h779-no
https://lh3.googleusercontent.com/wD-MaE...A=w1385-h779-no
 
1201-PNG1.png
 
Used a garden hose with drain open. Fired up the Jeep and let it sit running while I went inside. An hour later realized that I was in the middle of something. Came out, drained everything filled up with coolant, the radiator was once again leaking. Worked well, considering when I had the water pump off years later the water jacket was nice and clean.
 
I had previously used an over the counter chemical (Gunk C2124 Super Heavty Duty Radiator Flush) and was not impressed with the results. I used it about a week before the head gasket job.

The coolant is otherwise clean, there is just residual stop leak in there.

My region has extremely hard tap water, so I'm hesitant to use a garden hose.

And I'd rather not spend the money on the power flush tool.
 
Remove the lower hose or open the lower drain. Install that Prestone Super Flush T kit. Fill radiator with a cup of Dawn dish washing soap. Flush away till the water runs clean.

slomo
 
If you have the time, drain the radiator/block, fill the system with Evaporust, let it sit at least a day, drain, fill with water, drive, fill/drain with water once more, then refill with coolant. If not, Evaporust also makes a product that can be used while driving. If you don't like either one of those options, do a few fill/drive/drain/repeats with 50/50 vinegar. I will link the Evaporust products. I was up against a seriously contaminated system last year and these products worked better than anything else I tried, with vinegar being a reasonably close 2nd place.


https://www.evapo-rust.com/
 
This, the pellets stay in solution until they encounter air. GM used it in their factory fill. Not sure about aluminum powder, it will clog a htr core.
 
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