A buddy of mine has a jeep,still under warranty, with 14k miles. He wants the best oil and filter available, price does not matter to him. I told him to go with either Amsoil or Royal Purple, and a Mobil 1 filter, leaning more towards Amsoil oil. It calls for 5W20, but would it be fine running 5W30? It tends to be pretty hot where we live. besides warranty concerns, would this engine do fine on 5W30? it has the 3.8 V6.