I just purchased my second Jeep Wrangler (a 2011 Unlimited Rubicon). The biggest car mistake I ever made was getting rid of my 2005 Rubicon (you can't get the 4.0L straight 6 anymore).
Anyway, I was searching about recommended engine oils and came across this forum. After reading this thread I decided to join and post a reply.
I was suprised that there were no discussions about oil viscosity versus oil usage (and whether or not anyone had experimented with heavier oils to see if it helped their oil usage problem). I personally would have no trust in a 5W/20 engine oil unless I lived close to or north of the Artic Circle. Obvioiusly, this is a bit of an exaggeration, but if you do look at recommended viscosities versus temperature a 5W oil isn't absolutely necessary until somewhere near -20F. Now, I do run 5W/30 in my wife's Excursion in the winter but I switch to 10w/40 (Mobil 1 high mileage) in the summer. I just don't trust a thin oil to provide adequate film strength under heavy loads in the summer. It's probably adequate protection for bearings but it may not be adequate for the piston rings and cylinder. Does anyone remember the good ole days when we ran 20W/50? (I grew up in South Ga, very close to FL). What about the diagrams in the owner's manuals that showed 10W/30 oil good down to about 0F? The OHV engine hasn't really changed. The main reason OEMs recommend 5W/20 is fuel economy, NOT because it's better for engine protection (except in extremely cold climates).
For anyone who wants to learn more about motor oils for your car Noria corporation has a very good article available. Unfortunately it costs $15 but for me it was worth the money. It has more than 70 pages of information regarding motor oils and how to choose what's right for you (economics versus protection). Sometimes it's too technical (unless you are a chemical engineer), but most of it is very readable. Here's a link: http://store.noria.com/How-to-Select...load-P105.aspx
I am by no way affliated with them. I merely work in an industry (power generation) where I consider these kinds of articles professional development literature.
Somthing I learned is that multiviscosity motor oils are really thin oils that are made to act thicker and not thick oils that are made to act "thinner" in the winiter. If the VI's (Viscosity Improvers) shear down (which can happen but is less commen nowadays) you are left with an oil that is too thin to provide the necessary protection. When I bought my wife's 2003 Excursion from Carmax I went to a heavier oil at the first oil change. It made too much noise on start up. It hasn't been until the relatively recent past that general aviation aircraft started using multivisocity oils.
I haven't even seen the new Jeep I purchased as I'm out of the country, but after readinig this thread I've warned my wife to check the oil level every time she puts fuel in it.
Maybe this forum will replace my previous favorite (Turbodiesel Register) where I previously read and posted quite often.