You can use 10w30 in the summer. I suggest you purchase at least an owner's manual. Preferably a shop manual. Check out ebay.
GN4 Honda oil only.
10w-40 G4
Any kind of DOT 3 brake fluid.
A Honda 400ex is rated to hold 5 quarts of motor oil. This includes the oil stored in the oil pan and the filter which are replaced during an oil change.
i use a 20w-50 jaso rated oil. the 50wt. because its an air cooled motor
I prefer GN4 oil 15-40 weight. You can probably use whatever weight u prefer, but keep in mind that the thinner the oil the more likely your atv's clutches will want to slip (not good) -my400ex89 "Go big or go home"
On a 400ex the engine and transmission share the same oil. So when you change the oil in the engine you are changing the transmission oil as well. That is why you need an ATV or motorcycle oil designed for wet clutches.
about 2 qt.
1.9 us quarts
2.3 quarts
2.6 quarts
2.6 Quarts