Hmmmn I have been working in, and around, machine shops since I was 12 years old (Ya, back to the old overhead shaft, single motor powers the entire shop days!). and then as an engineer designing various machinery. I'm now 76, and recently retired, so that means 64 years of experience with mechanics, and lubrication. Everything I read on this forum, tends to show that people are draining the oil, and it seems to take about 2 1/2 quarts of oil to bring it up to proper level. All of the HD manuals, etc that I have seen say the oil capacity is 3.6 quarts..... Lets see..... 3.6 minus 2.5 leaves a quart +- of the old oil in the system. Where that is is a darned good question. It could be that the oil tank isn't draining completely, It could be in the crankcase. It could be in the oil passages, and oil lines, or most likely it is a combination of all of these places. Regardless of where it is, the end result is that only about 2/3 of the oil is being replaced when we do a "normal" oil change. I will concede that if an oil change is done regularly at the proper interval for the type of oil being used, it shouldn't make any significant difference. I suspect that is the, quite reasonable, assumption the people who wrote the HD manual made. I. also, suspect those same people assumed, as I normally would, that the amount that remained in the system would be a few ounces, certainly not a quart, when they said to ignore it.

Why that much is left in the system is a darned good question, with a myriad of possible answers. That it is left is, certainly, at a minimum, fairly common. If this problem was only in my bike, I would pass it off as a quirk of my bike (perhaps the scavenging pickup is not at the lowest part of the crankcase, perhaps the drain hose isn't at the bottom of the oil tank). The problem is that the fact that so many seem to be reaching full oil level with just 2 to 2 1/2 quarts leads to the conclusion that something is amiss.

Now, since I wrote my original post, I have been riding my bike regularly, although not too far each ride, and the oil has become quite a lot lighter in color, to the point that it is now pretty close to the color that I would expect it to be with the mileage it has been driven. I suspect this is because the new filter is working, and the old one was not working as it should have been. Perhaps the old one was plugged up, and being bypassed..... who knows.

My plan, as of now is to ride this for 2000-2500 miles, purge the old oil out to the best of my ability using the procedure I outlined in an earlier post, and fill it up with new oil, and a new filter. If it takes 3 quarts, or a little more, I will assume a lot of oil was left in the system in this last oil change. If it still only takes less than 3 quarts, I'll be damned if I know what is going on!