Question 75Motor Plants - 1st Asst/Chief

The correct answer is A) diluted with fuel oil. A decrease in the flash point of diesel engine lube oil indicates that the lube oil has become diluted with fuel oil. This is because fuel oil has a lower flash point compared to the lube oil, so the presence of fuel oil in the lube oil will reduce the overall flash point of the mixture. The other options are incorrect because: B) contamination with sludge would not necessarily decrease the flash point, C) dilution with water would increase the flash point, and D) contamination with carbon would not directly impact the flash point.