Thinking that Hurricane Dorian might head our way, I changed out the initial fill of Mobil1 10w-30 HM for some Rotella T6 5w-40 on Labor Day after 15 hours of shakedown runs on the target loads. Dorian passed us by, so on Saturday I thought I might give it a go with the T6 to see how it performed. Target loads means hooking it up to the home via a transfer switch and switching all available circuits over to the generator. This includes two refrigerators and a chest freezer. Just to make it interesting, I switched it into ECO mode and then fired up the dishwasher in a sani-rinse cycle with heated dry. Towards the end of that the gas oven went on, which requires electricity to run the ignitor and gas valve.
And the verdict is? For three hours generator was throttling up and down a lot, but never bogged down or stalled. My network infrastructure, meaning FiOS ONT and two downstream routers, never blinked.
This is completely subjective, but I think the motor sounded a little louder with the T6 than with the 10w-30. It could be my imagination, plus it was 74F vs. 90F the last time the generator had run on the 10w-30. Something tells me either would be fine for standby use.