I inherited a 2009 Jeep Liberty 3.7l with 40k on the odometer. I have read that the 3.7l can have problems with engine oiling in different ways and sludging. We used to have an older KJ which called for 5w30. This 2009 specs 5w20. Would there be any benefit running 5w30 vs 5w20 at normal intervals? I would assume (and you know what they say about that) the 5w20 switch was for efficiency / fuel economy? I just want to do my best to make sure I don't run into any avoidable problems with this engine which isn't generally held in the highest regard.