GM engine 5.3 L83, mileage 365k and some change. The engine is clean, praise be to God. I am its first owner, and it has never been opened. I change the oil at most every 5,000 km with 0w-20 oil. I have never changed the viscosity since I bought it, and the oil is rated for 10,000 km, but I change it at 5,000 km. The reason for selling is (modification project).