Oil change interval, why is there a time limit?

It won't hurt anything if you run it closer to your 15,000 mile interval. I just changed mine today and it had just over 7,000 on it since the last change. I just change mine annually because it doesn't cost much since I do it myself. I know Cummins says 15,000 miles between changes but it might take awhile for me to get comfortable with putting that much mileage on my oil.

All it takes is to spend a few bucks for an oil analysis. That will tell you if your oil still has any life left in it and will help you make an informed decision in the future.

Timely post, lol.

I just changed the oil in my C7 Cat and 7500 Onan yesterday. The book gives variances on miles based on usage. It's been 1 year and 8 mos since I the moho and had ALL the fluid & filters changed.
Well, I changed the oils and filters yesterday (made a HUGE mess as usual BTW) but, the engine oil had 8k miles on it, the genny had 270 hrs on it. Genny book says 500 hrs, I figured a year and some change wouldn't hurt.

Since I’m not an expert I follow manufacturer’s recommendations ..miles, hours and/or time. I trusted GM (or Chrysler) with a bunch of money...now disbelieve them on oil changes? Does Artum have an opinion on voiding the warranty for failing to change the oil? If “it should last the miles” is good enough for you... Isn’t for me.

I think many people park their rigs during winter, and if you have used the oil since the previous winter started, it's good to change it. But if you are a regular user, and run it for awhile every month for an hour or more, it should last the miles.