Dirt in radiator from?

[el 56]

Hello gentleman, I am hoping someone can identify what is in my radiator. Engine was rebuilt recently and a new radiator was installed. I noticed after several miles that my radiator had dirt in it. I drained the cooling system but the antifreeze did not mix with the dirt. I then, flushed the system with prestone flush and water but the dirt did not mix with the flush either. My question is where did this come from and how do I clean out the cooling system. Could this be a blown head gasket? The antifreeze looked perfect coming out and the oil in the crankcase looks fine and not contaminated. they only thing I could find was one spark plug that looks suspicious. appreciate any help and advice. Thank you. Videos below of dirt and spark plug.
https://www.youtube.com/watch?v=JRrOlMB ... ZaIww&t=0s
https://www.youtube.com/watch?v=AgQgrnC ... WVWAfZaIww

https://www.youtube.com/watch?v=H_Z0Ss6 ... WVWAfZaIww
https://www.youtube.com/watch?v=0YqZcEN ... WVWAfZaIww

the oil on the threads of the spark plugs is from when i install the plugs, I drop oil on the threads so the plugs wont seize on the heads.

[Kevin Johnson]

What is the history of the car and engine?

[el 56]

engine was given to me from a friend that had is laying around for a few years. He pulled it from a junkyard. It's a SBC 400. I had the engine sent out and rebuilt. Dropped the engine into my car. Drove the car a few thousand miles and noticed the dirt in my new radiator that was installed when the rebuilt engine was.

[Kevin Johnson]

Get a powerful magnet and see if the dirt is ferrous and sticks to the magnet.

All sorts of stories about what can be in old blocks sitting around for years (rodent infestations, etc.). Do you know for a fact that the block and heads were hot tanked when it was rebuilt?

[rebelrouser]

What kind of coolant did you use? Dexcool and other organic type coolants use acids to make a protective coating in the engine, if air bubbles are present it will form a brown muck, ask any GM dealer technician. GM lost a class action lawsuit about their coolant right before they went bankrupt. Your video looks like the same muck. I have had some bad experience with water wetter type additives as well. I had them eat out the seals on my electric water pump on the race car.

http://www.sancarlosradiator.com/dex-cool.htm

[Krooser]

I've seen that crap several times... I simply pulled the t-stat unhooked the lower rad hose and flushed it out for about an hour. Don't stop until you know it's clean.

Same with the radiator.

[JoePorting]

I assume it's coming from the block. There are two drain plugs on the bottom of the SBC block by the oil pan on either side. Pull them out and rinse out the block. They are 1/4 inch NPT plugs, so hopefully you have a four point plug socket.

[Roundybout]

How are the hoses? I had an old farm machine that had crap in it from the hoses internally breaking down. It looked like that.

I don't know what's going on with that plug though. Almost looks like a liberal dose of anti-seize on it.

[midnightbluS10]

You can always add a couple drops of Dawn soap into the cooling system. It's always worked great for me when flushing that shit out of GM engines. Its never caused any issues, either. Last one I did looked like someone took a handful of mud and shoved it into the radiator cap opening, it was so bad. Took all afternoon to flush it all out, but it eventually came clean.

[Kevin Johnson]

Dishwasher detergent and washing machine detergent (note both are machines) are generally low-foam. Foam is typically intended to hide dirt from the human user.

My Father did work on a foaming surfactant intended (initially) for bore drilling for atomic warheads. The foam was very stable and intended to lift tailings out of the bore hole. I don't think foam is needed here.

[Dave Koehler]

looks like the usual rust crud we used to see up to the 80s.
As the man said previously a major flush is in order until it is gone.

[rfast racing]

It could be from stop leak pellets that come in gm crate engines. I've also got them in some reman engines too they are just like the bars leak ones. As far as radiator flush a little clr does a pretty good job on rust in the cooling system

[midnightbluS10]

They also put stop leak pellets in installed engines at the factory, from what I understand.

[SupStk]

I'm wondering if the block was hot tanked and rinsed. When pressure washing its not unusual to see all sorts of crap flushed out of water jackets.
Also curious if it was in the radiator and heater core when the new engine was installed?
A good flush is called for here.

[huero]

I appreciate all the advice gentlemen. I was really worried it was a blown head gasket. I will look into trying to get all the crude out. Can’t thank u all enough.