To convert from the green stuff to the proper Zerex G05 coolant is a time consuming process, but well worth it.
This is what I did...
First I drained the radiator and block. I pull off the small hose that leads to the expansion tank to drain the radiator. If you don't have an expansion tank, pull off the lower radiator hose. Once the radiator is drained replace the hose. The block drain is located on the right side of the block in front of the starter. It takes a 19mm socket. You must remove this as most of the old coolant is still in the block and will not come out via the radiator.
It helps to put the car up on ramps.
Next I removed the thermostat, but left the rubber ring in place.
Then I flushed the system with hose water by attaching a 1/4 inch galvanized pipe nipple approximately 3 inches long to the engine block drain. I then threaded an elbow and a six inch pipe nipple to the one in the block. I cut off some old garden hose and clamped it to the six inch nipple. This way I can back flush the system.
Once I had this set up, I started the engine and turned on the defroster. With the hose running, I flushed the block until the water coming from the expansion tank was clear.
Next comes the flushing steps to remove any rust and grease in the system.
Put the block drain back in.
Fill the system with water by removing the top radiator hose from the radiator and filling it until there is water at the top of the hose, replace it and fill the rest of the way from the expansion tank.
Next put in a cup of Tide detergent. Start the car and run it with the defroster on for about 1/2 hour. Let it cool down then repeat the water flush steps until the water is no longer soapy.
Replace the thermostat. You can reuse your old one if, when you put it in a pan of boiling water it opens fully. I went with a 75 degree one when I replaced mine. It is normally for a 1970's vintage 450, but it works fine in a OM617 engine.
Next you want to do the citric acid flush. drain the system and fill it with a mixture of two gallons water with 2 pounds of citric acid dissolved in the water. (it helps to use very hot tap water to dissolve the acid powder)
Run the car with this as the coolant for a week.
Repeat the steps to flush with water. You will be amazed at the garbage and rust that comes out when you back flush the system. I flush with water at least three times, letting the car cool down between flushes. (don't want to burn yourself )
When the water is clear and does not feel 'slippery' the acid is gone.
Now you can fill the system with 50% Zerex and 50% distilled water.
If you always use the fill from the hose method, you should not have air bubbles in the system.
To purge out any air in the system during any of these steps, put the car on ramps or at least point it uphill. Remove the expansion or radiator cap. Start her up and get her up to operating temperature. Turn on the defroster. Rev her up to 3000RPM a few times. The air should come out of the system.
I know it is a lot of work to do these steps, but you will thank yourself for it when you see how dirty the acid flush water gets. Remember, if you use the correct coolant, you will not have to do this again
