Cummins X15 vs ISX15 April 23, 2017, 04:56:58 pm Beginning with the 2018 Cornerstone models, the ISX15 will be replaced by the updated X15 platform. The ISX platform had only one 15-liter option, the X series offers two: The fuel-friendly X15 "Efficiency" Series geared toward line-haul and regional markets, and the X15 "Performance" Series, built specifically for heavy-haul, RV and other demanding applications.Several hardware changes were made to improve performance on the X15 engine, including a high-flow EGR cooler and piston cooling nozzles and exhaust valves to improve reliability. The X15 Performance Series now boasts 605 horsepower in its top model. That is right 5 more HP for 2018 Cornerstones!Increased braking power has been made available through out the full operating speed of the engine, especially from 1,300 to 1,700 rpm, right where you need it the most. So now you will get more engine braking at normal driving rpms.They have also introduced the Single Module aftertreatment system with the X series. This combines all exhaust cleaning functions (VOC, DPF and SCR) into a single canister. This saves up to 60 percent space and 40 percent less weight than the previous aftertreatment system. Improvements to the DEF doser will provide an improved spray pattern to reduce DEF consumption, how much will be interesting find out as the ISX15's consumption can be rather healthy.The oil change, oil filter and fuel filter service intervals have increased. Cummins rates oil change intervals for RV's at 15,000 miles or 12 months. Fuel Filter change interval is 15,000 mi or every 6 months. Typical RVers will have to change based on time vs miles so you may not see any benefits here.