9 Cummins ISX Problems [ISX12, ISX15] Oil Capacity

The Cummins ISX diesel engines are used in RVs and trucks.

Owners have reported these problems:

  • Leaking EGR valve
  • Camshaft flattened
  • Cracked and Dropped cylinder liners
  • Turbocharger lags
  • excessive oil consumption
  • Excessive smoke, white, blue, black
  • Timing wedge fails
  • Rough idle
  • Lack of power

Video explaining various issues:


isx12 Specs:
6 cyl
385 – 650 hp
1450 – 2050 lb-ft
bore 130mm, stroke 150mm
2660 dry weight
48 qts of 15W40 oil


isx15 specs:
6 cyl
400 – 450 hp
1450 – 1750 lb-ft
bore 137mm, stroke 169mm
18.9:1 compression
50 quarts of 15W40 oil
dry weight 3186 lbs


You can change the oil with these tools:
1/2 inch wrench to remove drain plug
drain pan

It is a solid engine that can last for 300k miles or more with a rebuild. One owner has reported 1.5M miles.

The ISX is used in Monaco Signature and American Eagle Motorhomes.

It looks like this: