I am the second owner of this Jeep and I have had it for the last 30,000 miles. I change every 5000 miles with 10 w 40 and have not had any issues yet. Good oil presure no noises and no leaks YET, I dont have to add any between changes. I'm good with it. My wifes 09 Liberty takes 5 w 30 I think. I dont change it dealer does.

 

This is just my 2 cents, from working in an auto parts store for the past year...unless you have had the vehicle from early mileage...I would say less than 40,000 miles, I would not recommend running a full synthetic. Full synthetics, no matter the weight, are much thinner than conventional, or even high mileage oils. This is a debate that could go on for days, months, years even...My suggestion, run what motor oil you feel comfortable with. I have 216,000 miles on my jeep, it does have a valve cover leak, I do occasionally see small oil spots in my garage. I run 10w40 Mobil Clean 5000, with Lucas Stop Leak, every oil change. I have even debated switching over to Rotella T 15w40...I do not change weights for winter or summer and have no problems. I think I read your jeep has 140,000 miles...my best suggestion, if you have no leaks, no other issues with your 4.0...stick to Jeep specifications...

 

Bottom line is this... As you can tell ten people are gonna give you ten different answers on this site. If you like conventional, then go with it,,, and if you like synthetic, run it

 

Anywhere from 5W-30 up to 10W-40. Choose your brand, enjoy the jeep.

Personally, I say 5W-30.

 

There's no such thing as a viscoisity chart for synthetic oil and a different chart for conventional oil. Why would, lets say 5W30 synthetic be "thinner" than 5W30 conventional? It's not......just one of the many oil myths.

 

Alright guy I'm pretty sure I'm gunna be using valvoline 10w-40

 

....but why?

 

 

155,000, I run 10-30 and Lucas oil additive.

 

Because the thicker oil helps with the rings on your piston better and I'm using the Lucas additive too works good

 

Because the thicker oil helps with the rings on your piston better and I'm using the Lucas additive too works good
And valvolines been around since the beginning of cars lmao I thought that was pretty cool

 

 

Says who?

In engines lubrication is not about adhesion, its about flow. Hence why I recommended 5w-30.

 

Ok listen take 5w-30 and 10w-40 and put some on two different figures there's not that big of a difference buddy just compare them and if you run 5w-30 take your oil cap off and Yal see like a smoke come out of the oil hole on the valve cover that means your running to thin of a oil 10w-40 will help with that and let it run for ten minutes or soo then take the oil cap off and let me now if what I said happens alright bud

 

And by the way who told me this great information would be my automotive teacher at fscj and I understand what your saying but a little bit thinker oil helps alot