Hi all, new to the forum as a registered user, but I have been driving down the oil nerd rabbit hole of valuable information on here for at least a year, and I'm hooked! Thanks to all the contributors here for their great advice and frankly civilized behavior compared to many forums out there. I recently lucked out purchasing an 8kw (running) portable generator from 1991 with a US assembled Vanguard 16hp V twin with force feed lubrication and an external oil filter. Some farmer ran it for 45 minutes when he bought it, changed the oil, and stashed it in his basement for 18 years under a tarp! I have taken this generator to it's knees over the course of a 4 day on and off power outage a couple weeks ago running water pumps, heat pumps, and even the dryer. Started out with synthetic 5w30, but I want something that will stand up to the high oil temps I will see as this thing will sometimes run for a couple days straight. It is set up to run on propane as well, and I am having a 120 gallon tank brought in just for the generator, so fuel dillution shouldn't be an issue (I don't think). The generator is in a kind of lean-to shanty against the side of the house, it has lots of airflow, and the exhaust is ducted outside of it, but it still gets to be 70 plus degrees in there when the generator is running even when it is below freezing outside. My issue is I may need to start this thing and run in super cold temps, I live in NW Washington, but I could see temps approaching 0Â°F, but then once it's up and running, it will be toasty warm, and powering the whole house, potentially for a couple days at a time. Not quite sure where to go. My thought is to run a decent 5w40 synthetic like T6, or Valvoline PBE, which I could probably have on hand for my truck (6.7 Cummins). I currently run Valvoline PB 15w40 conventional in my truck as I only do 5k OCI about annually, but I may start blending in one jug out of three of PBE 5w40 synthetic to get a better winter rating, so I could have both on hand. I can't justify running different oil in the cold months (in the truck or the generator really) as I will only be doing annual oil changes unless I rack up a ton of hours during an exceedingly long power outage. I'd love to hear some opinions of 5w40 synthetic vs 15w40 conventional (or something else that might work better) in this application considering how hot the oil will get, and how many hours I can stretch out the OCI on this thing since it has a nice spin on oil filter. I probably ran for a total of 50 hours in 4 days this last go, but ya never know, it would not be impossible to wind up needing to run for over 100 hours straight. Thanks! I have attached the Vanguard oil recommendations as well.