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#4622225 - 01/02/18 09:08 PM Flushing out stop leak
jamesm113 Offline

Registered: 05/20/11
Posts: 20
Loc: CA
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:

#4622244 - 01/02/18 09:29 PM Re: Flushing out stop leak [Re: jamesm113]
Linctex Offline

Registered: 12/31/16
Posts: 6148
Loc: Waco, TX
"The evidence demands a verdict".
(Re:VOA)"it's nearly impossible to actually know the particular additives that are in there at what concentrations."

#4622262 - 01/02/18 09:39 PM Re: Flushing out stop leak [Re: jamesm113]
Dyusik Offline

Registered: 09/26/14
Posts: 1984
Loc: US-WA
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.
95 Cherokee 190K DELO 10W30,XG8
07 IS250 97K FB ?w??,FULL
04 YZF-R1 19K DELO 15w40,XG7317
99 HD XL1200S 18K VR1 20w50,1515
14 RX450h 30k PP 0w20,NAPAG

#4622347 - 01/02/18 11:50 PM Re: Flushing out stop leak [Re: jamesm113]
The Critic Offline

Registered: 08/30/04
Posts: 19808
Loc: CA
If you really want to spend the money, buy one of these:
2011 Toyota Prius - 168k - ServicePro Dexos 0W-20
2007 Honda Accord 2.4 - 128K - Idemitsu 5W-20

#4622784 - 01/03/18 02:04 PM Re: Flushing out stop leak [Re: jamesm113]
jamesm113 Offline

Registered: 05/20/11
Posts: 20
Loc: CA
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.

#4682494 - 03/02/18 04:39 PM Re: Flushing out stop leak [Re: jamesm113]
slomo Offline

Registered: 08/23/13
Posts: 164
Loc: Oklahoma
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.


#4684648 - 03/04/18 09:38 PM Re: Flushing out stop leak [Re: jamesm113]
TurboTravis Offline

Registered: 07/26/07
Posts: 207
Loc: NY
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.

#4684653 - 03/04/18 09:42 PM Re: Flushing out stop leak [Re: jamesm113]
philipp10 Offline

Registered: 05/09/14
Posts: 1181
Loc: Minnesota
Will cleaning this "gunk" out extend the longevity of the car? I highly doubt it. I'd leave it be.

#4684880 - 03/05/18 07:59 AM Re: Flushing out stop leak [Re: jamesm113]
andyd Offline

Registered: 09/25/04
Posts: 7158
Loc: Marshfield , MA
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.
'16 Camry LE STP synth 0w20 and STP filter. the Fridge

1994 Ranger ,the Rat, 5w30 dino, STP filter

'16 Camry SE, Valvoline HM 0w20 and OEM filter
Thick oil is better grin2