Fishy, not removing the oil fill cap and thereby not allowing the atmospheric pressure inside the engine to equalize is not going to allow the oil to flow out as quickly or as thoroughly, leaving some dirty oil in the engine. This will definitely cause more damage than the millions to one odds of a leaf, etc., blowing into the oil fill hole. I mean, that could happen when topping off the engine oil level too as the oil fill cap has to be removed. I sure hope you top off the engine oil and don't let it run low for fear of a leaf blowing into the oil fill hole? :blink:
Take a sealed gallon of milk and punch a hole into the bottom. The milk will leak out, but not very quickly. Now take the top off that gallon of milk and the milk will come gushing out the hole in the bottom much, much faster as the atmospheric pressure has been equalized. The same principle applies when performing an oil change; removing the oil fill cap, pulling the dipstick before removing the oil pain drain plug and oil filter.
When performing an oil change, removing the oil fill cap and pulling the dipstick before removing the oil pan drain plug is standard operating procedure for any competent auto center. In other words, this is the way the pro's do it.:thumbsup:
As for the o-ring, he addressed that, stating the oil drain plug for his car has a permanent gasket attached to the oil drain plug.
However, he did neglect to mention about eating his Wheaties for breakfast!