is crankcase oil cleaning necesary?

This is a big yes, because the oil on the crankcase becomes contaminated with other fluids and solid waste, if you don't change the oil regularly or at manufacturer specs. your engine will ruin before of time.

You replace the oil and filter in a motor every 3,000 miles and that is necessary!

Only if there have not been proper oil changes.

No. No manufacturers recommends crankcase oil cleaning in their maintenance procedure. They do however recommend regular oil change intervals. As long as you use good quality oil at the correct weight and replace it as recommend, you will never need crankcase cleaning.

Oil does 3 things; lubricate, cool and hold contaminants.

yes

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