I have run water injection on various engines since about 1978. In small doses, it is very effective at cleaning the piston heads. I currently use in on my 87 300D I run on vegetable oil, and on my 93 cummins 5.9 6BT that also runs on 100% waste vegetable oil. I use it to keep the pistons clean and to reduce the tendency for the vegetable oil to gum up the pistons. I set the system to use approximately 1 gallon every 300 miles.

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Turbo300Mercede
87 300D W124
83 240D W123
80 300 TD Wagon W123, 4 Speed from 79 240D, SLS Rear Suspension