we have a 2010 GC with the 4.0L engine....according to manual and the cap it requires 10 w-30 oil....i was wondering if it is ok to try 5w-30??? i am looking for better fuel mileage.i have tried synthetics at that grade but no real change...in the old manuals in cars they used to list alternative grades depending on climates but the CD manual doesn't..thanks for any suggestions...

 

Engines these days are pretty picky with the oil. If it specifies 10w-30, then you use 10w-30 or get other issues.