its very easy. theirs a oval plate underneath the gen , take the screws out and the drain plug is in their. open the gen door and remove the cover and the fill tube is their. here in Florida I use 30-w oil just over a quart. theirs is no filter on the 4000 gen. you should have a manual in your thor pouch.
Did you receive the generator manual in the bag of manuals from Thor that the dealer was supposed to provide? The maintenance section details everything you need to know about periodic maintenance and service.
Ed & Bev Felker
Retired USAF Col and retired Nurse
Traveling with Lily & Bella ('Teddy Bear' breed)
2015 Vegas 24.1 (E-350)