I've seen a lot of posts, and I want to know how to tell if mine are on their way to needing replacement.
I'm suffering from: very slight rise in oil level, 2 mpg drop in mileage, no smoking on startup, no rough idle issues.
IF they're going bad, are they covered on the 100k Cummins warranty? Im now at 80k and don't want to miss the boat if they're something I can get covered...

 

Best thing to do is pull a sample and send it in for analysis. That will tell you if there is fuel in the oil. I had 2.5% fuel at one time and the dip stick never showed it and it never smelled like diesel. But there was a problem. Drop in mileage might be from fuel filter etc. But yes your engine warranty covers injectors to 100,000

 

Thanks very much, that's exactly what I was looking for. I just changed the oil so I'm going to get 1000 or so mi on it then send it in.
Thanks again