A new motorhome owner with a Cummins X15 engine, experiencing recurring high oil temperature alarms and engine shutdowns, shared their recent experience on a motorhome forum. After a recent oil change and following advice to “run it like you stole it,” the owner embarked on a 180-mile trip through Arizona. This journey provided valuable insights into the X15’s oil temperature behavior.
Observations on the Road
Initially, the oil temperature gradually climbed to 259 degrees Fahrenheit before stabilizing and then decreasing to around 239 degrees. After a lunch stop, temperatures remained in the 240-255 degree range. However, during a significant mountain climb, the temperature exceeded 262 degrees, triggering a check engine light (CEL) but no shutdown. The CEL extinguished itself once the engine crested the hill and the oil temperature began to fall.
Understanding the Cummins X15 Oil Thermostat
Based on this experience, it appears the X15’s oil thermostat opens around 259-260 degrees. The CEL likely illuminates when the oil temperature surpasses 260 degrees, indicating the thermostat isn’t opening quickly enough or the engine control module (ECM) is programmed too close to the 260-degree threshold. The owner hypothesizes that the rapid temperature increase during the climb might cause a delayed thermostat response.
Cummins X15: A Different Engine
Cummins acknowledges that the X15 runs hotter than other engines in their lineup, with a higher oil cooler and thermostat setting. While the X15 handled normal driving conditions well, the CEL during the mountain climb raises concerns. The owner plans to continue investigating this issue with Cummins and Spartan.
Oil Analysis Results
An oil analysis performed at SPEEDCO revealed a clean bill of health with two warnings related to oil viscosity (V40C and V100C). Further investigation is needed to determine if the viscosity is too high or too low, but initial speculation leans towards excessive viscosity.
Next Steps
The owner intends to contact Cummins and Spartan again, armed with the new data from the road test and oil analysis. The goal is to determine if the 260-degree thermostat opening point is appropriate for the X15, or if adjustments to the thermostat or ECM programming are necessary to prevent high-temperature alarms and potential engine damage. The investigation into the viscosity warnings will also continue. This ongoing dialogue with Cummins and Spartan will hopefully lead to a resolution for the high oil temperature issue in this Cummins X15 powered motorhome.
