Drained the oil on 2003 Fatboy for oil change. Refiled oil tank and could only put 1.5 quarts back in tank before it ran out filler spout. What would cause the tank to not drain completely? Bike was o

Oil feed line goes from bottom of oil tank to lowest engine fitting
Oil return line goes closest to oil filler spout and then inboard of oil feed line on engine
Breather goes next to return line but inboard of it and then to highest engine connection near lifter cover.

If I remember right, your oil tank is under the transmission, which has two drain plugs.

You might have removed the one for the transmission, so check it's fluid level.

Stand the bike upright. Remove the dipstick from the oil tank. Remove the drain plug on the bottom right side of the frame. While the oil is draining, replace the oring on the drain plug. Remove and replace the oil filter, after filling the new filter half full of oil. Replace the drain plug. Put 3 quarts of oil in the oil tank. Replace the dipstick. Start the bike and check for leaks. No leaks, you're done! I use HD Syn 3 synthetic oil in my '04 Fatboy, but you can also use a conventional 20w50, as long as it's made for use in and air cooled motorcycle. Don't use car oil!

The Oil Capacity is 3.5 qts. (3.3 L) are you sure you pulled the right drain plug, and drained the ENGINE oil? The engine oil drain hex bolt is located on the right side of the motorcycle and is removed/installed horizontally.
Transmission oil drain hex bolt is located on the left side of the motorcycle and is removed/installed vertically.

From the right side of your bike, look for a large hose coming out of the backside of the oil tank at it's lowest point. Follow the hose down behind the transmission on down to a clip on the lower tube of the frame behind the exhaust pipes. There is a metal plug in the hose. Simply take the hose out of the clip and reroute it below the frame. Remove the plug and the oil tank filler cap and the oil will drain out. Refill with three quarts of 20W50 oil.

Good Luck
Steve

On the softail model Harley Davidson's the oil tank is external and sits up higher than the engine crank case and oil pump. when these bikes sit for an amount of time the oil gravitates from the tank to the crank case. starting may seem sightly harder and seem like the battery is going dead. the bike should be started in knowing that you had oil in it to start with and no giant leak puddle underneath of it. warm up the engine and then drain the oil out of the tank. the reason why your filler cap popped off is because you had probably 2 1/2 to 3 quarts to much engine oil in the bike. so drain the oil from the tank at the drain pug at the bottom of the hose on the high (right side ) of the bike where the swing arm meets the frame (it is a 5/8 socket) put the drain plug back in run the bike for about 5 minutes inspecting with a flashlight continuously that oil is circulating back into the tank. then dran it again and replace with new oil.

The oil pan is on the bottom of the transmission on your Dyna Wide Glide. To change the gasket start by draining the engine oil and transmission lubricant by removing both plugs on the bottom. Once drained, disconnect the hoses going to the oil pan. Remove oil fill cap, remove two screws and remove the oil spout, pull up on the dip stick cover to remove it. Now, remove the allen head bolts and remove the oil pan. Replace gasket and all bolts. Torque all bolts to 7-9 foot pounds. Refill with oil. Transmission take 20-24 ounces of transmission lube and the oil tank takes 2 quarts 14 ounces of oil if you did not replace the oil filter. Since the oil filter is still full of oil, if you put the full three quarts of oil in the tank, the oil cap will blow off when the oil gets hot as it's overfilled. Good luck

Are you sure you pulled the right plug. How much oil came out?

Probably didn't hurt it, my 2002 was ran for 2000 miles 1 1/2 quarts low on oil due to dummies putting only 5 quarts of oil back in it after changing the oil. It takes 6 1/2 quarts. It didn't hurt it at all.

Fatboy, drains from the oil tank bottom right side rubber tube goes down to frame, bolt in frame is plug. Have to get to it from underneath. This is only engine oil. After oil change three quarts, if change filter 3.5 quarts.
Hope this helps.

JP