Harleys don't mix oil with their gas. Harleys have "dry sump" oil systems; instead of there being an oil pan in the engine, a Harley has an oil tank under the seat. The grade you want is 20W50.
Increase circulation and oil cooling. Not all Harleys have external tanks
No.
the crankcase vents through the breather system.
Typically its either worn or broken Piston compression rings.
on all Harleys prior to the twin-cam the oil pump has two lines attached.the one closest to the outside is always feed to the oil pump and it attaches to one of two stubs at the bottom of the oil tank. The other line that attaches to the oil pump is the return, and unless it routes to and through an oil cooler, it goes to the top of the tank, next to the large round cap under the seat. the other stub underthe tank is the breather line and it goes to the nipple just above the oil pump. Another nipple pokes out behind the oil pump. It goes to an end breather filter, or to oilt the rear chain.
to read a oil tank you have to get a oil stick that its long and then put it in the oil tank
The oil pump moves the oil from the tank through the engine and filter and returns it to the tank the way the heart circulates blood.
Some truckers use the oil from an oil change as added fuel in the tank. In this case it will Not ruin your tank
No oil tank inside the house.
It depends on experience of different oil tank removal company.
When does an oil cooler work? When air is blowing through it. When is the oil too hot? When it is idling in heavy traffic. That is the reason HD doesn't install oil coolers on Harleys, though they will sell anything that you will buy, as that is the business they are in.