I have seen several posts about servicing Onan generators with attempts at writing a walk thru for service. I just completed service on my 12.5 hoping the pictures assist.
1) Once you have the cover off, drain oil remove dip stick oil will drain faster, R&R oil filter. Refill oil 6 quarts
2) Remove three bolts holding coolant reservoir, leave cap on and remove, leaving all coolant lines attached.
3) Air filter can now be accessed, R&R air filter. Be sure to place cover with one way valve facing down
4) Fuel filter remove two bolts on side and remove filter, place over oil drain pan and R&R lines (you will note the lines are different sizes) they can't be installed "backwards"
5) I leave the fuel filter out to check for leaks
6) Push and hold "off" switch after about 2-3 seconds you will hear a click and the fuel pump will run. (generator won't start) Hold for 15 to 20 seconds checking for leaks and re-priming filter.
7) Start generator, check for oil leaks, fuel leaks and general operation.
Congrats you saved $$ and now your doing your own basic generator service.
https://drive.google.com/drive/folde...3Te48JpYbNfXCk