The two pictures above show socks that have been placed over the exhaust pipes of a diesel-engine pick-up truck and a BlueHeat Coolant Heater. The dirty sock on the left was put on the exhaust of a 2005 diesel-engine pick-up truck for 10 minutes. The clean sock on the right was placed on the small exhaust pipe of a BlueHeat Coolant Heater. This is by no means scientific, but it is interesting to view the difference.