I have tried Blue Devil, and the Evaporust. I did use Cascade dish washer powder. All worked to a degree or so. The Evaporust came out black. I still had some 'dirt' in the engine. This was on a Jeep 4.0L. I do think the Evaporust does remove rust or converts it. The Oxcylic acid sounds interesting.
I'd probably start with Prestone for a cheap clean and degrease. Then Evaporust or the Blue Devil Complete. If that don't get it, then Citric Acid or the Oxcylic acid.

Don't Rush It
 

Leave the cleaner in there for a few days worth of driving to let it work really well .

Ive used the commercial cascade powder product and also simple green to remove greasy sludge from a cooling system, they work great. But only work if you know a few ways how to flush it.

A difficult example is a nissan qr25de which has two thermostats. Most mechanics dont know or bother to remove the block drain plug which is hidden near the power steering pump. (Old model as new are ehps)

If you dont remove that plug and dont remove the bottom thermostat elbow, you will not be able to flow water and debris from those spots.

For super plugged cooling systems, oxalic acid works great too. If you have leak stop mud in the system then the red 20 minute coolant flush sold at commercial parts stores is the one you want.

But again, you need to work out how will you get liquid in and out of all the galleries.

Simple Green
 

It specifically states DO NOT USE HOT WATER so I'd not think using it in any cooling system would be wise .

For the jeep 4.0 engine, you need a zero charge coolant filter as it has the same issue as old toyota 1fz engines of land cruisers.

It has some heavy contaminants in it from the factory which dont come out with flushing, the filter catches all those as they get picked up and pushed around.

We may have scared the OP off with all the horror stories :D

I left them over night at times. It was earlier in the year. The temps were getting down near freezing. Also, I did not have the Jeep plated at that time. So I did not drive it much. I let it idle for 1/2 hours or so. Still, point taken. I do think I had a dirt build up at the rear cylinder wall water jacket. I notice this on another 4.0L when I did freeze plugs. Still, when I took off the water pump to hose it out, it looked clean.

Lol nope, I'm still here. I've read the posts and will go through with the plan I have formulated. It was maintained at Mercedes for a long time before I bought it by the service manager who owned it, so I'm confident a simple flush will fix me up. I have no overheating issues or anything, so this should be a simple preventative maintenance. I am going to have to find a picture of what the block drain looks like and exactly where it is (all I've been able to find is its near cylinder 5) so I can attack it quickly and get it drained. I have a turbocharger right in the way so I can't see it from the top and I don't want to be under this car forever fiddling with trying to figure out which part of the block is which 😁

Sounds like a plan! :)

Block drain is on the passenger side of the block, towards the rear. Encircled in yellow in this pic:

https://encrypted-tbn0.gstatic.com/i...mcsRA&usqp=CAU

From this thread:

http://www.peachparts.com/shopforum/diesel-discussion/251889-om603-what-these-pictures.html

That's exactly what I needed! You've been a huge help, thanks!

How many different engines did you use to test the different soap solutions?
 

I think that might be an important factor because if you used several soap solutions then used the citric acid you followed the traditional method of degreasing the engine cooling system before using citric acid.

I also wonder if the interweb research included petroleum oil rather than pig fat and veggie oils.

I'd like to see the data on your extensive research.

I have used the old hot rod method. Floor stripper one gal. in cooling system with water. I removed thermostat. Let run 30 minutes drain refill 4 times with one gal vinegar, and two times plain water.

Sounds like something someone who works for Big Soap would say. :laugh3:

Honestly just giving another data point, and an offhanded one at that. I'm just telling you, in my experience, greasy cooling system parts get the most clean with citric acid alone versus the popular detergents alone. Easy to test if you want, or not. I literally don't care.

But also, dish and laundry detergents aren't exactly designed to break down petroleum either, so it's not a surprise to me that they didn't work all that great. This is really more about the detergents and less about citric acid. Might as well run Purple Power through the cooling system if we're so fixated on oil being in there.

also, you can run pure 100% white distilled vinegar in the cooling system for a few days of actual operation, then drain and flush.

BIG SOAP?
 

Citric acid is a good cleaner. I showed photos of the soap cycle and the 10% citric cycle on a thread a while back. Soap indeed did part of the job.

If there's an issue with cleaning an engine cooling system it's the process. Drain fill, drain fill drain fill. It took me better part of a week to do each cycle using first water to rinse the system, then soap to try and knock some of the crud down, then water to rinse the soap, then citric acid to finish the crud removal the water to rinse the citric acid out. I used a sump pump to circulate the liquids and let it pump for about 15 hours each cycle.

Each cycle required me to remove the block drain plug. I can walk out now and remove that plug without getting under the car. I know, that's something to brag about, right?

There are probably many ways to clean an engine cooling system but being that I'm 69 yr/old and probably won't ever do it again I tried to follow all the rules and use the best method I could find.