The power vent on top of the water heater is designed to mix enough room air, with the combustion air, to bring down the temperature of the combined air, so that it will be low enough to be vented in PVC. If the blower screen or wheel becomes filled with dirt/lint the air flow will be reduced, causing the unit to overheat. You can clean out the power vent using compressed air or with a vacuum cleaner

The motor itself usually has no oil ports to worry about.