Flushing and coolant debris

[tmsmini]

Strange issue on a rebuilt engine...It appears this block did not get the full "cleaning" treatment on rebuild. I ran plain water at first and it soon become very dark with rust. I used Liquimoly for the first flush and then rinsed a few times, after running for 15 miles or so, the water/coolant was dark again. Thermocure was suggested. Again same thing. This time I collected the waste from the flushing as my wife as not happy with the rust stains on the driveway. I found the debris at the bottom of the bucket.

I have flushed three times with a chemical flush and rinsed at least five times between flushes and I am still getting debris and rust. The debris is mildly magnetic so I am assuming it is rusty debris.
I am ready to do another chemical flush, but I am not sure the results will be different. More pictures in the link


https://photos.app.goo.gl/27ikqv5eruRvZigw7

[94touring]

I will run a pretty strong solution of distilled water and phosphoric acid for a couple days of driving.  This is after initial flushes with a hose. The inno coolant is still completely brand new looking a couple years later.

[MiniDave]

That looks like sand to me, how the heck did that get in there?

I agree, you have to leave the solution in there for a while, not just in and out again.

[tmsmini]

Both flushes have phosphoric acid in them. At least one for sure as it is listed on the MSDS. The other MSDS says proprietary ingredients. The flushes are in for at least 5 days and one one was in for over 100 miles. It really looked like sand to me. At first I thought the phosphoric acid was just turning the rust particles dark. The debris is somewhat magnetic and I am not sure if the phosphoric acid changes the magnetic properties of the rust particles at all.
I will do another flush and see what happens.

[mascher]

The blocks and cylinder heads are cast in sand molds. It's common to find small pockets of sand in complex castings and they can remain for decades and be released apparently for no reason or when  cleaned in an aggressive way. I've pulled a shocking amount of sand out of 50 year old heads water jackets.

Kelley

[MiniDave]

Well now see, there you go!   

[tmsmini]

I wondered if sand casting was a probable cause. This Thermocure is pretty aggressive. I will let it work for a week and a hundred miles or so and then rinse it out. It takes a lot of rinses and temp/pressure runs to clear it.