Liqui-Moly Radiator Cleaner or RMI-25?

[JHZR2]

I’m going to address the cooling systems on my new 91 350SD, and the 91 300D that I’ve had a few months.

Would like to clean and flush the cooling systems before I take them both over to John Deere Cool Gard II. This can be a slow process over many months as the cars get driven and I have time. I’m thinking while it’s still warm to do a water flush and use a cleaning agent. Any recommendation? These are iron block aluminum head engines so I’m a bit sensitive to that.

Any thoughts?

 

[Trav]

Cheap citric acid powder.

 

[Greasymechtech]

RMI doesn't need to be flushed out. Add it, drive, and drain/refill your coolant in the future. Never have to worry about residual RMI25.

I don't use or recommend flush chemicals.

 

[JHZR2]

Cheap citric acid powder.

Ive done that on my cast iron diesels. Wasn’t sure about aluminum head engines.

 

[Trav]

That was my fear until I see MB was still using it in the later mixed metal engines, since then I have used it in all sorts of mixed metal and all aluminum engines with no issues. No worries, I buy it on Amazon.

Use about a lb per gallon capacity or 10%.

https://www.amazon.com/Spicy-World-Citric-10-Pound-NON-GMO/dp/B002DCPR9C/ref=sr_1_19_sspa?keywords=citric+acid+powder&qid=1665058584&qu=eyJxc2MiOiI0LjExIiwicXNhIjoiMy45MyIsInFzcCI6IjMuODYifQ%3D%3D&sr=8-19-spons&psc=1

Drain the cooling system of all the old coolant
Remove the thermostat and replace it with a "forcibly-opened" thermostat p/n 000 589 63 00
Connect a flushing connection pipe (a tee) p/n 117 589 00 90 00 between the upper radiator hose and the radiator
Connect a tap water hose to the tool fitting
Open the surge tank cap
Set the heater to defrost on cars with automatic CC so the aux coolant pump runs
Start the engine and run it at 2500 RPM
Open all drain plugs and turn on the tap water to maintain a full cooling system at all times while the engine is running
Flush for 5 minutes to remove all old coolant
Shut off engine, shut off tap water, and allow cooling system to fully drain
Install radiator and crankcase drain plugs
Dissolve citric acid powder in 5 liters of water
Fill cooling system with solution and top off with water, bleeding as necessary
Install surge tank cap and start engine
Run engine for 15 minutes at approximately 2500 RPM and blip throttle occasionally
Make certain that coolant is flowing through radiator and heater core.
Open cooling system drains again and turn on tap water to flush cleaning solution from cooling system
Start engine and run at 2500 RPM for 5 minutes to flush all cleaning solution from system
Shut off engine and remove special tool from upper radiator fitting
Reinstall normal thermostat
Make sure that all drain plugs are installed and tight
Remove the surge tank, flush it separately, and reinstall it

 

[BMWTurboDzl]

I’m going to address the cooling systems on my new 91 350SD, and the 91 300D that I’ve had a few months.

Would like to clean and flush the cooling systems before I take them both over to John Deere Cool Gard II. This can be a slow process over many months as the cars get driven and I have time. I’m thinking while it’s still warm to do a water flush and use a cleaning agent. Any recommendation? These are iron block aluminum head engines so I’m a bit sensitive to that.

Any thoughts?

Citric acid
CLR Radiator Cleaner (Lower PH than citric acid)
Prestone HD Cleaner.
CRC Radiator Cleaner

I was looking at these products myself a couple of weeks ago. IIRC all of the above state a 10 minute idle for cleaning. That way you don't have to worry to much about letting the engine cool before flushing out the solution with cool water.

 

[JHZR2]

That was my fear until I see MB was still using it in the later mixed metal engines, since then I have used it in all sorts of mixed metal and all aluminum engines with no issues. No worries, I buy it on Amazon.

Use about a lb per gallon capacity or 10%.

https://www.amazon.com/Spicy-World-Citric-10-Pound-NON-GMO/dp/B002DCPR9C/ref=sr_1_19_sspa?keywords=citric+acid+powder&qid=1665058584&qu=eyJxc2MiOiI0LjExIiwicXNhIjoiMy45MyIsInFzcCI6IjMuODYifQ%3D%3D&sr=8-19-spons&psc=1

Drain the cooling system of all the old coolant
Remove the thermostat and replace it with a "forcibly-opened" thermostat p/n 000 589 63 00
Connect a flushing connection pipe (a tee) p/n 117 589 00 90 00 between the upper radiator hose and the radiator
Connect a tap water hose to the tool fitting
Open the surge tank cap
Set the heater to defrost on cars with automatic CC so the aux coolant pump runs
Start the engine and run it at 2500 RPM
Open all drain plugs and turn on the tap water to maintain a full cooling system at all times while the engine is running
Flush for 5 minutes to remove all old coolant
Shut off engine, shut off tap water, and allow cooling system to fully drain
Install radiator and crankcase drain plugs
Dissolve citric acid powder in 5 liters of water
Fill cooling system with solution and top off with water, bleeding as necessary
Install surge tank cap and start engine
Run engine for 15 minutes at approximately 2500 RPM and blip throttle occasionally
Make certain that coolant is flowing through radiator and heater core.
Open cooling system drains again and turn on tap water to flush cleaning solution from cooling system
Start engine and run at 2500 RPM for 5 minutes to flush all cleaning solution from system
Shut off engine and remove special tool from upper radiator fitting
Reinstall normal thermostat
Make sure that all drain plugs are installed and tight
Remove the surge tank, flush it separately, and reinstall it

So, the other question for this is if I need to use a flush at all vs just a lot of drain and refill.

Neither system has any cooling performance issues, I have more history of running the 300D in the heat with AC, but both are working well.

Is it worth the complexity of that job vs more drains and refills at this point?

That’s why I was thinking about a more gentle long term agent like RMI-25… if anything at all…

Thanks!

 

[Trav]

If its clean I would just drain the radiator and pull the block drain then vacuum refill. That is about all I would do, not a fan of multiple drain and fills for any fluid, get most of it out and refill.
Edit: The block drain is probably just in front of the starter or under the front near the mount shock 8mm allen.