I use a small centrifuge. Oil is heated by a 2400 watt 120V water heater element. Fluid circulation is accomplished with a Toyota Camry power steering pump driven by a 1 hp 120V motor. Pressure regulation is accomplished manually using a bypass circuit. Oil is heated to 155 degrees F with thermostatic regulation. Oil returning to the tank from the filter is dumped onto a flat plate and allowed to splash before returning to the tank to encourage moisture and light solvents to separate and evaporate. Oil viscosity prior to the start of cleaning is measured and adjusted using a drip test similar to checking paint consistency before spraying. Used gasoline engine oil or ATF is filtered separately from used diesel oil. Diesel oil has much more soot and the dispersants it contains work against the soot settling out. The end result is that obtaining clean waste diesel oil takes more energy so I filter it in smaller batches.

Most people seem to use the logic that the OE fuel filter is 10 microns so filtering to some nominal smaller micron size is sufficient. This completely neglects the quantity of smaller particles which may be present after filtering. Running a large quantity of small particles through a system designed for clean fuel will still cause wear. Just because 1000 grit sandpaper won't remove paint quickly doesn't mean it can't damage a finish. I have tried filter bags, paper, carbon, screen, and several other methods to clean oil and I feel the centrifuge is the most time and energy efficient to get oil to a point that I feel is acceptable. The only thing I'd like to change is to switch to a larger centrifuge to clean the diesel oil better.

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