Dieselsmoke

The most desirable temperature to properly combust diesel fuel is around 650 degrees. At idle you might be running around 200-300 degrees, not quite enough to properly burn the fuel. What happens is called "wet stacking" and if done often enough can cause damage. If you have to leave it running for extended periods of time just to like was mentoned above, use your hand throttle to keep the RPM up a bit.

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