It has been a long time , but we used water methanol (ADI, anti-detonation injection) on the R-2800-CB16/17 on the Convair 440 and the DC 6.
I also recall using water methanol on the Darts on the Viscount 806X and the Convair 640. The Convair 580's that were with Frontier also had water methanol injection. We leased a couple of them, and they were different in that regard.
Most of the time we had barrels of water methanol available, but if there wasn't any we used straight water. It nede a flush afterwards.
I have heard of incidents with the Darts were the wrong fluid was used (in one case jet fuel, in another Varsol cleaning fluid); resulting in dual engine failures on take off.