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..

huh.. what did you pay for? I wonder if they should have kept at it until it was clean. that would annoy me

muric acid is nasty stuff to clean out.
don't do it.

find a brewing store near you, pick up a pound of citric acid. 6 bucks when I got it and a gallon of vinegar.

get a big hose to bypass your radiator and pull the thermostat.

dump about a qter of each in and water in and run it for a bit, then let it sit till tomorrow.

drain and flush it again. you might have to do that a couple of times.

then get the seats in the hotrod.

When they were done it looked pretty good.

There was a little coolant spilled on the radiator. It was a typical bright green. The coolant that backed up through the open cap was green but a shade or two darker than what was spilled on top.
It was not the mud slide brown stuff that came out of the engine when I got there.

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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.

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Especially if you start dumping acids in to clean everything up.

My 318 flushed clean, but still had a couple inches of crap behind the freeze plugs.

My GY3 71 Challenger was a California car for nearly 30 years. Apparently they never used antifreeze, because the cooling system suffered from the same thing you're describing. It's a small block, and had a leaking freeze plug in the back of the block. I was going to fix it when I replaced the transmission, but when I popped it out and saw what was inside.. I pulled it out, removed all the freeze plugs and used a pressure washer to clean out the block. About a half a yard of crud came out! Installed brass freeze plugs, and put it back in the car. I had the radiator flushed and put it back in, and never had anymore trouble with it gunking up. I know you don't particularly want to pull it, but that may be the best option. It will cost you more time than money. Good luck.

I have heard of people having good luck with Cascade, no joke.

I'm with JDMopar on this one ... the block is going to have to come out ,be disassembled, and cooked clean.
I had a 73 440 that was the same way , I must have flushed it a dozen times and got the same result, when I took it apart and pulled the freeze plugs the area around the cylinders were solid with sediment ...