I just did mine and am very satisfied with it. I'd go ahead and change out the thermostat if you haven't recently.

You should drain as much old coolant out as you can, take out the thermostat, put the housing on, and flush out the rest of the bad coolant with water. You'll need to repeat the fill, run, drain exercise to get all the green stuff out. Make sure and turn on the heater. Then add the Prestone superflush and follow the directions.

I didn't get all the old coolant out when I put the Prestone flush in, so I think that the old coolant/gunk nullified the flush. I really think you need to take out the thermostat and flush the system with water to make sure and take full advantage of the flushing.

I'm going to have to redo mine to get all the oil out.

Once you run the flush for the prescribed run time (6 hours), you need to repeat the process of drain, fill with water, run, drain. Then fill with Zerex.

And, the Zerex coolant isn't that expensive and I got it at Pep Boys.

Sholin

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What else, '73 MB 280 SEL (Lt Blue)
Daily driver: '84 190D 2.2 5 spd.