I believe what you and others are seeing is not casting sand, but tiny bits of the block due to insufficiant cavitation protection.

The 7.3's were very bad at this and all diesels are prone to this to some degree. Its caused by the block vibrating and tiny bubbles form in the coolant passageways. Every time a cylinder fires these bubbles explode so to speak, eventually taking small parts of the cast with it.

This is the danger switching to an ELC type coolant after a VC-9/Restore + flush, it completely removes all cavitation protection and with this type of coolant it takes up to 5,000 mi. for the cast iron to be completely protected.
With a HOAT coolant with low silicates protection happens almost immediately, which gives it quite an advantage over other formulations.

This may or may have not happened in your situation, but it does happen and the cavitation protection shouldn't be removed unless there is some sort of failure internally requiring it.

Cylinder Liner Cavitation Erosion
The cavitation erosion that is found in diesel engines on the exterior side of the cylinder liners (wet) has been a theme of
investigation by engine and corresponding component manufacturers, even though no definite manner of eliminating
the problem has been found. See item 1.
The degree and size of erosion or decay as well as its form and
distribution on the affected zones can vary from engine to engine
and inclusively from cylinder to cylinder within the same engine.
The affected areas form vertical strips or patches sometimes in alignment
with the thrust face of the piston within the cylinder, or also formed
immediately over the top sealing ring of the liner. The erosion can
penetrate the wall of the cylinder and permit the flow of antifreeze/coolant
to the oil or vise versa.
The cavitation erosion is caused by excess in harmonic vibrations of the
engine and in some cases by loose fitting liners that result in a fast
formation and implosion of small vapor bubbles within the coolant which
attack the cylinders’ liner wall. The vibration in combination with collapsing
bubbles produces an erosive effect over the surface of the liner’s exterior
face. This occurs as the piston moves up and down within the cylinder
causing vibration especially over the area of thrust in the cylinder liner.
We can say that the wall of the sleeve, which comes in contact with the
coolant, quickly moves inwards and outwards striking these vapor
formations. During this process, tiny bubbles are formed that implode or
collapse violently producing shock waves against the liner’s wall. The results
of these implosions at the impact area of the liner’s wall have been calculated
to reach over 10,000º F with pressures of over 10,000 psi.
A specific material, which would prevent cavitation erosion within reasonable cost, has not yet been found.
Nevertheless, some coatings can be applied to delay cavitation erosion until it is time for major engine repairs.
In order to reduce or prevent cavitation, manufacturer recommendations should be followed.
In many cases, cavitation can be avoided by reducing harmonic vibrations. For example, by making sure the
injection complies with the manufacturer’s specifications, the engine’s speed is governed according to the
manufacturer’s data and that the control functions. Also, do not underestimate the importance of correct
clearances between liner and cylinder blocks; incorrect liner fit is a serious contributor to liner vibration resulting
in cavitation erosion.
Engine manufacturers have specific additives for the coolant called SCA (supplementary cooling additive). These
additives will form a protective coating over the cylinder liner, which is exposed to the coolant, therefore reducing
cavitation damage. With time, additive concentration reduces in the system, consequently making it necessary
to follow system maintenance recommendations in order to keep the adequate levels. The following points will
be supplied:
• pH control to avoid corrosion
• Water hardness control to avoid mineral deposit formation
• Cavitation protection
In all cases, it is required that all manufacturer’s recommendations regarding coolants, base additives, additives,
coolant filters as well as maintenance schedules should be strictly adhered to or followed at all times.

I found this, its a brief explanation into this subject.

Well one thing I should of added to my post is the easy to tell if it sand or metal
is a magnet. Put the "sand" in a baggie and place a magnet on the bag. Lift and
see if the bag sticks or not.

Sean :-drink

Unless the metal is aluminum..

True.
But
There are ways to make you talk }> :-hair
Then you go by color & weight.

If you really want to get into it some very simple
chemistry will tell you if it is or is not.

Sean :-drink

Interesting.
It is definitely metal coming out of mine. That's how I got it out of the 5 gallon pail – with a magnet.
I can remember on my old 7.3 that the SCA stuff was recommended, so I used it, but I hadn't read that it is recommended for this engine with the Ford Gold coolant. Is that the case? Can it hurt?

I backflushed my heater core. Absolutely nothing out of it. Nada. Zero. Zilch. Cavitation.... wow... who knew that we'd be arguing over ELC and HOAT? Man, this is just too much for one day.

I was not trying to start anything between HOAT & ELC coolant types, only laying the facts out for everyone to see. The article I posted refers to "wet sleeved" engines, (which our 6.0's are not) but it does happen in all diesel engines to some degree.

As I posted earlier, the 7.3's were known to shed iron due to cavitation. After reading the article it made me wonder, is the specific tunes some of you are running causing an increase in harmonic vibrations leading to the cavitation?

For those of you that did the VC-9 flush and switched to an ELC were you aware that cavitation protection would be delayed for up to 5,000 mi.? I am not saying that one type of coolant is better than the other, but there are inherent risks stripping your cavitation protection off and switching chemical composition.

I went to elc cat ec-1 because that's what international puts in these engines, and they make these things. I believe ford uses gold because they didn't want to stock another coolant type.

If it's good enough for international, it is good enough for me.

Duplicate post

Wow, some info to ponder here. I had no idea there was 5000 mi until the cat coolant coated the engine. Is there any additive we can add that is compatible with ec1 and will give us the protection ASAP???

I think I'm still missing something you drove to a ski resort (Isn't that up hill)??? EOT high of 222 and an 18 degree difference putting coolant at 204 this does not sound out of line to me at all. help me understand what I miss read here?

You posted two different things with conflicting and dated info. Your supposition of Block material (your 1st post) is not supported by the aged information supplied on your second post which did apply to early 7.3s when they let SCAs drop...

No the info isn't conflicting or dated, my second post is an article referring to wet-sleaved engines. The SCA is still required in the Ford Gold, and the Cat ELC speced coolant it is supposed to be checked also, with additives available for both formulations.

The advantage of the newer speced coolants is to run LONGER before needing to check/add SCA, not to eliminate them.

I thought Cat EC-1 coolant was silicate free. I know there is an additive to enable it to run longer, but isn't it silicate free?