Just picked up a new (used) moho and taking it out tommoorrow might and I noticed the oil in the genny is a bit low. I just want to top it off until I get back to drop it and tune it up. What type of oil do I use?

Here's the Onan Specs. I use 10w-40 with 100hr change intervals.

TABLE 1. OIL VISCOSITY VS. TEMPERATURE EXPECTED AMBIENT TEMPERATURES
SAE VISCOSITY
GRADE
32° F (0° C) and higher 30
10° F to 100° F (–12° C to 38° C)
15W-40
(OnaMaxTM)
0° F to 80° F (–18° C to 27° C)
10W-30
10W-40
–20° F to 50° F (–28° C to 10° C) 5W-30

ONAN suggests using ONAN oil 10-40 they have Valvoline Mfg the oil for them and they have ANTI FOAM AGENTS ADDED to the oil. The crankcases of the Generators typically only hold 2 to 2 1/2 quarts of oil and because of the RPM they can foam causing engine damage. Onan only suggests going to the heaver viscosity when you have like a 1500+ hours on engine or if you are consuming lots of oil