I just bought a 2005 Nissan UD 245 series truck. It runs well, no smoke, no water in engine but when I open the radiator capp I found a fair bit of oil in the water. I flushed the radiator and filled it up with new coolant and ran it for 20 minutes only to find loads of oil in the radiator again? Could I have a problem with my oil cooler, water pump or do i have a blown head gasket or a cracked engine...I need some basic advice before i rush off to mechanic and open my wallet. you help is much needed.