In addition to being a cold starting aid, the grid heater on the 5.9L Cummins reduces emissions while the engine is cold due to the fact that more complete combustion occurs with heated air than air at ambient temperature, particularly while the engine is below operating temperature. The secondary benefit is reduced cylinder washing (wet stacking) while the engine is cold and therefore less fuel dilution during the warm up process.
Heater Grid Cycle Times
The following chart outlines the operation of the grid heater on the 12v 5.9L Cummins diesel.
Intake Air Temperature |
Heater Grid Cycle Time |
Post-heat Cycle (engine running) |
>59° F |
No cycle |
none |
59° F - 15° F |
~ 10 seconds |
yes |
15° F - 0° F |
~ 15 seconds |
yes |
<0° F |
~ 30 seconds |
yes |
Grid Heater Deletes for Cummins Diesels
The heater grid is not a particularly restrictive device, although it can be removed in favor of increased airflow, less air turbulence, and therefore the potential for more power. A heater grid delete is a machined or cast spacer designed to replace the heater grid between the intake manifold and air horn. The modification is not permanent and can always be reversed by simply reinstalling the heater grid. As such, this modification is something Cummins owners can try, test, and remove if the results are unsatisfactory - the heater grid delete spacers are not particularly expensive. Many suggest that performing a heater grid delete can yield measurable increases in boost.
The disadvantages of deleting the heater grid include:
• Difficult cold starts - The heating grid is a cold starting aid. While an engine may still start at low temperatures without the heater grid, it will be more difficult to start and the engine will take longer to reach operating temperature. The heater grid reduces starting effort in ambient temperatures below 59° F.
• Cylinder washing during warm up - Low intake air temperatures, combustion temperatures, and increased warm up times will increase the likelihood and severity of wet stacking while the engine is cold.
While the modification is recommended for high performance applications and/or warm weather use, it's a relatively simply upgrade with the potential to increase performance. Actual horsepower/torque gains will vary considerably, with heavily modified engines benefiting to a higher degree.