This study explored the effect of oil dilution with biodiesel and ultra low sulfur diesel fuel on acidity and corrosion in two lubricants with API service ratings of CJ-4 and CI-4+. The oils were diluted to levels of 0%, 5% and 10% with ultra low sulfur diesel fuel (ULSD), 20% biodiesel (B-20) and 100% biodiesel (B-100). For each case, the mixture of fuel and oil was subjected to oxidation tests using a procedure similar to ASTM D6594. The oxidation resistance of the CJ-4 and CI-4+ lubricants was similar in each case. The advanced formulation of the CJ-4 lubricant gave comparable overall performance to the CI-4+ lubricant, despite reduced levels of metallic additive compounds. The highest levels of lubricant degradation occurred when the lubricants were diluted with B-100. A substantial increase in acidity was observed when the oils were diluted with B-100. Moderate levels of copper and lead corrosion were observed in the tests with no fuel dilution, and dilution with ULSD. An order magnitude increase in corrosive wear was seen in the tests with B-100. Lower corrosion occurred with the CJ-4 lubricant.

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