If the used oil sample smells burnt, is the oil bad?
If the oil smells burnt, it is possible that some fuel has contaminated the oil. Check to see if the oil also feels thin and if so, send the sample of oil to the lab for verification. The oil needs to be changed only if there is substantial fuel dilution, resulting in a viscosity drop of greater than 15% of its original value. If the viscosity drop is not so substantial, the oil can continue to be used, as a certain amount of fuel dilution (below 4%) is not abnormal. But inform the vehicle owner about this fact and request him to get his truck engine checked.
