Found this over at Valvoline-Technology.com
Link Here
Thermal Characteristics of New and Used Diesel Engine Oils
SUMMARY:
Used diesel engine oils were found to have increased thermal conductivity in comparison to new oil. The magnitude of the effect is dependent on the concentration, size and dispersion of soot particles, as well as the oil composition. While soot in the engine oil is generally deleterious to engine performance for wear and deposits, no negative effects on thermal performance of the oil itself, indeed even slight positive effects are expected, for oils which maintain soot in stable dispersion. The relevance of this finding to thermal control in modern diesel engines is briefly discussed.
Link Here
Thermal Characteristics of New and Used Diesel Engine Oils
SUMMARY:
Used diesel engine oils were found to have increased thermal conductivity in comparison to new oil. The magnitude of the effect is dependent on the concentration, size and dispersion of soot particles, as well as the oil composition. While soot in the engine oil is generally deleterious to engine performance for wear and deposits, no negative effects on thermal performance of the oil itself, indeed even slight positive effects are expected, for oils which maintain soot in stable dispersion. The relevance of this finding to thermal control in modern diesel engines is briefly discussed.
