Pre-warming a diesel’s coolant allows the engine to start cleanly and emit lower levels of pollutants compared to cold starts, and extends the duty cycle of the exhaust system’s diesel particulate filter, according to tests sponsored by Webasto Thermo & Comfort North America, a maker of coolant heaters.
Emissions from two cold-start tests, one at 40 degrees Fahrenheit and the other at 75 degrees, were compared to pre-heated, 155-degree starts of a 2005-model International DT-466 diesel running on a dynometer. Metering of the exhaust showed that pre-heating the coolant resulted in.

  • 27% fewer particulate-matter emissions compared to the 75-degree “normal ambient” start and 66% fewer PMs versus the 40-degree “winter” start;
  • 29% reduction in carbon monoxide during winter conditions, and a 62% reduction during normal ambient conditions;
  • 40% fewer NOx emissions; and
  • fewer particulates sent to the filter, which extends the time between required cleanings and saves maintenance money.

Pre-heating the engine does not have a significant effect on hydrocarbon emissions, said the test results from ESW America Inc., an independent laboratory. The coolant heater was a 5-kilowatt Thermo Top C provided by Webasto.  

“The independent testing results show that pre-heating engines improves DPF performance and longevity, along with extending the duration between cleaning cycles on engines that do not run a heavy duty cycle,” said a statement from Webasto.
“Even engines in warm climates of 70 - 80 degrees Fahrenheit, for example, are not completely warm until they reach 130 degrees Fahrenheit and higher for optimal performance. Webasto coolant heaters provide optimal temperature at start-up.”