Obviously, it best to prevent sludge from forming in the first place:

  1. Use a good quality engine oil.
  2. Change the engine oil at regular intervals.  Use the manufacturer's recommendations or use Used Oil Analysis to determine the optimum extended oil change interval.

  3. Plan your trips so that the engine reaches its normal operating temperature as much as possible.

  4. Keep the engine in good tune (ignition timing, carburetor jetting, etc)

  5. Keep the PCV (Positive Crankcase Ventilation) and EGR (Exhaust Gas Recirculation) systems in good working order.

  6. Keep the cooling system in good working order.  Use the recommended thermostat or even consider using a winter thermostat.

 

Often, people acquire cars with engines that have not been well maintained and poorly maintained engines can be severely sludged.  Sludge is not a problem if just coats the interior surfaces of the engine but, if it ends up clogging the oil pump's pickup screen, it can cause severe engine damage.  I recommend using modern, fully-formulated (ie, with additive packages meeting non-obsolete API service categories) engine oils in all engines newer than 1930 because modern oils minimize engine wear and prevent sludge formation.  See Impact of Low Quality Oils on Engine Wear and Sludge Deposits.   The use of non-detergent oil (API SA, formerly ML - Motor Light) is only recommended in vehicles earlier than 1930.