the best way is to fill the crankcase with diesel fuel to the top .... turn the motor over for a while with the plug out and the ignition disabled .... drain and refill with oil .... good to gooooo

 

The diesel fuel trick works every time, that is what I use when doing a blown head gasket that leaks coolant into the oil on a car/truck etc..
it really cleans things up and breaks down the sludge.

then a couple oil /filter changes