Well I may be a country bumpkin rube, but seems to me, Chrysler Engineers that designed and tested the motor might know more about the best oil viscosity to use in their motors than Ferrari Owners and Mechanics.
Of course 0W-20 might work fine in your motor, why don't you post your oil pressure readings for different ambient temps, engine temps, rpm and load? And we'll compare.
There's a saying in the Engineering and Test communities; One Test is worth a Thousand Expert Opinions
. Chrysler did a Multitude of Testing, and your Ferrari Forum, you don't have to read half his post to realize the guy is NEVER going to address individual application and actual result, and stay in the general. So, let me think, hmmm, yea, that was hard, I'm going with the Manufacturer's Recommendation.
The 0w-20 will flow better in cold temperatures - yet still provide the protection of the recommended 20 weight when fully up to temperature. An excellent selection regardless of where you live.
Synthetic flows betters at all temperatures, especially cold, than conventional of equal viscosity, so just switching to synthetic of the same viscosity would provide those benefits.
Overlay or compare the viscosity charts for 0W-20 vs 5W-20, you'll see the viscosity is lower at all temps up, often even at the 100° mark and past it as well.
Oil is NOT digital, multi-viscosity does NOT mean it magically changes to a different viscosity oil when it reaches another temperature. Multi-viscosity oil means its an oil with modified viscosity, they plot the measured viscosity and describe the modified viscosity by what reference oil viscosity it is closest to at 2 different temperatures, low and high.
Plot one line with points (0,0°) and (20,100°) and another line (5,0°) and (20,100°) you'll find the 0-20 is lower than 5-20 the entire range until they converge at 100°, and although its actually a curve, its the same thing, 0W-20 will be a lower viscosity through just about its entire temperature range than 5W-20, except at its high temp measured point.
As well, to achieve a wider viscosity range often requires the use of more additives that are especially the ones more likely to sheer and degrade with use and time and burn, leaving deposits in the motor. The sheering of the additives causes viscosity to drop faster and the oil to degrade faster and protect less the longer it is in the motor. Narrow range viscosity oils also tend to broaden the band of higher viscosity and drop off less in viscosity at the higher temp points past the high temp measuring point. If anything, if several multi-viscosity oil meets the conditions you operate, its more advantages to pick the narrower range of viscosity.
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Don't get me wrong, switching to 0W-20 is NOT that big of a change from 5W-20, especially if you are also switching to synthetic. Good quality oil and more frequent oil changes are going to eclipse the slight viscosity difference in protecting your motor.
BUT, far better qualified people have tested your motor and found the best viscosity oil to use, they published their recommendations in a book and put it in your glove compartment, so why NOT just read it?
OR you could go to a Ferrari forum and listen to someone tell you his analysis of oil, totally isolated from the individual application, which he NEVER address's, and decide he must know more about your Jeep than the engineers that designed and tested it.
If anything, the manufacturers have been leaning toward the lowest viscosity possible for energy savings ratings, I don't know why you would want to go lower, unless your operating in temps far lower than intended for you vehicle.
How are those Ferrari tires working out on your Jeep? I mean if Ferrari owners use those tires, it must be better than lowly old Jeep Engineers select for your Jeep.
How is your tornado air system doing creating all that extra HP? and those Extra Energy Spark Plugs? After all, we all know the engineers designing cars never try this stuff, if a 5 dollar part really made an extra 25HP, they would never think to include it with the vehicle as OEM.
Please, this is the thinking you get when people start musing about oil viscosity and how they know better than the designers that tested the motors, as too what would be the best oil viscosity to protect your motor. Its all B.S., like I said before, if your experimenting with different than recommended oil viscosity and do NOT have an oil pressure gauge on your vehicle, IMO, you're a FOOL. And if you're one of those people, I have a Tornado Gas Saver to sell you, its just a little piece of sheet metal that will improve your gas mileage and make more power.
Cause the guys selling this know more about your Chrysler Engine than the engineers that designed and tested it, thats why this works.