<p data-pm-slice="1 1 []">Buying a used Nissan engine without thorough inspection is one of the most financially damaging mistakes any vehicle owner can make. Always begin by requesting complete mileage documentation and import certificates, particularly for Japanese domestic market sourced units that typically carry lower verified mileage. Request a compression test to confirm consistent cylinder pressure readings throughout the entire engine. Carefully inspect all external surfaces for active oil leaks around valve covers, oil pan seals, and the rear main seal area. Check the dipstick oil carefully for any milky contamination indicating head gasket failure. Research model-specific issues before purchasing. Only buy a used Nissan engine from suppliers offering a minimum thirty-day warranty with clearly enforceable return policy terms.