More cooling system cleanliness issues

I had the Imperial's cooling system flushed again today. Once more, what went in green came out looking like mud.

I'm really not sure what else to do about this thing.

The car sat for 14 years.
Heater core was bypassed long ago. It leaks.

I drained the icky coolant (not pure water) and refilled.
The car ran hot.
Radiator flush from the parts store was used.
Car still ran hot.
Hoses and water pump were replaced. Radiator recored.
Block drains were pulled. Water was run through block until it came out clean. Engine was fired up with block drains open. When the block drained clean water it was revved up to blast out nasties. Both drains would spray filth. This continued until only clean water came out. It took the better part of an hour to do this.

The car was driven about 4,000 miles and taken to a shop to do a radiator flush. The coolant looked like mud.

Today, 10 months (and 2,000 miles) later, the same shop flushed the coolant again. The coolant looked like mud.

The coolant went in bright green. When the engine was started and brought up to temperature the coolant was noticeably darker than it went in. I think it's on it's way to becoming mud again.

No stop leak products have been used as far as I can tell.

Short of pulling the engine and doing a complete tear down and chemical bath how can I get the cooling system clean?

No, the transmission cooler is not leaking into the radiator.

Did you try adding vinegar or a mild acidic?

engine oil getting into coolant?

I had the same problem with my '81 Dodge D150 with a slant 6, and the heater core by-passed (150,000 miles) I flushed it out and used GM Prestone Dex-cool extended life antifreeze/coolant. After 5 months...no more sludge! I can still see thru it the coolant when I open the radiator cap. It is translucent red in color.

Can you get at the freeze plugs ? Pull a couple on each side and get in there with a hi pressure hose ???

It's not getting a milkshake. Oil contamination is not an issue. It just seems to be full of rust and other nastiness.

I had all the receipts from the original owner. The car never had any major work done. No notes were made concerning the heater being bypassed. The AirTemp II servo was bypassed as well. It has the cracks that are all too common. The heater hose was simply doubled back and connected to the water pump housing.

The car had 65,000 miles when I bought it. It is now at 71,000.

I have not tried acids. The flush I bought had an acid base.

I have avoided pulling the freeze plugs. There is no good way of getting to them in the car. I would have to pull the engine. That is not high on my to do list.

Is it overheating? If not what does it matter that coolant looks like mud?

The car runs nice and cool.
If it's hot outside and I'm running the A/C on the freeway it will run warm but not dangerously hot.

I want the cooling system clean to help the engine stay cool and reduce the chances of clogging an ultra hard to find radiator and heater core.

Maybe I should install some sort of coolant filter.

do a reverse flush yourself or take it to a garage you trust that has a coolant exchange machine. It sounds like this is driving you nuts, as it would me, so maybe you are at the stage where you would spend some money just to move beyond it.

I would not mess with the freeze plugs. In my opinion that is a nuclear option

I've been known to drain the system, put in a gallon of vinegar top off with water, run till warmed up and let sit over night, then do a power flush. However, that I reserve for mildly crusty engines not sure how it would work for you. But one thing does come to mind. If it's that rusty internally then the original steel freeze plugs are probably iffy at this point. You may just be on limited time till one starts leaking.

its probably loaded up with an inch or 2 of rust at the bottom of the block behind the freeze plugs. I had a 383 with the same thing.You can probably tell where and how much with a temp gun. I did pull the motor due to gasket leaks and at that time i used Mauriac acid to clean it out, not sure i would use it in a running motor maybe if it was very diluted but that would be a lot of fill and drains..

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do a reverse flush yourself or take it to a garage you trust that has a coolant exchange machine.

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I had a local shop with a coolant exchange machine do their thing twice.
Their guys were fairly disgusted at what came out of the radiator.