I stated in some other threads here recently concerning high oil consumption and associated issues (carbon in the head porting & combustion chambers, pinging, etc) with the 3.8L that I intended to make the switch to a higher viscocity oil once my warranty expired. Well, did an oil change a couple of days ago and threw in 6 quarts of Shell Helix 15W40, & I thought I'd breifly share my findings here.

Wow, what a difference; it is like someone opened the hood one dark night & snuck in a 3.6L Pentastar while I wasn't looking! Motor runs smoother & quieter than it ever has before with absolutely no sign whatsoever of any of the usual ticks & taps from the valvetrain, seems to be more responsive and more powerful (according to my seat-of-the-pants dino) and according to the readout (I'll know for sure when I do the manual calculation the next time I fill the tank) I'm actually getting better mileage (an extra 1.5MPG) than I was on the 5W30, even though the reason Chrysler specifies the thin oil is purely because it's supposed to get an extra half MPG.

It's too early yet to tell if there is any change in oil consumption through the PCV system but I'll know in 3 or 4K miles when I next change it out again; I pulled the PCV line & flushed it out with degreaser so it's clean as a whistle now, so I'll know for sure when I pull it again at the next oil change to inspect it. Obviously I can get away with running a higher viscocity oil as I'm in a hot climate, & the 5W20 that Chrysler specifies is a winter-weight oil suitable for below freezing temperatures. What I need is an oil that protects better at the extreme operating conditions that my JK sees over the summer months (110F ambient temps and extended periods of idling in traffic during this hot weather, high RPM & low gears in 4WD on the beach, etc). I also specifically chose an oil that does not conform to the latest "emmisions friendly" API specifications as it contains higher levels of anti wear additives (zinc & phosphorus) that these newer oils aren't allowed to have (because zinc & phosphorus apparantly wear the cat converters out faster).

So all in all, very pleased. I don't even have 50K miles on my JK yet however the motor felt like it had done closer to 100K miles running that thin oil; it now seems much happier runing an oil of a thicker viscocity that this motor was originally designed by Crysler to run on before they changed the spec to the thin stuff for "economy reasons".

 

I live in Houston where most of the year it is 90F plus. I have often thought of using 10w-40 like I did in every other car I have owned for 30 years. Next oil change I might just try it.

 

I'm interested in knowing how this works over time. Anything that helps that poor little engine be all it can be gets me listening.

 

Sounds interesting. I had never considered this but might give it a try. I am in a hot climate as well so you make a good point.

 

x2, I just got the last of my "dealer included/service warranty/free" oil changes. My next oil change is out of my pocket and I am going to a heavier synthetic (Royal Purple)

 

I noticed a significent decrease in engine noise when switching to 5w-30. I'v sent off a sample of my used oil since switching, and every wear metal is within universal averages except for copper, which seems to be excessivly high in every UOA (used oil analysis) I have seen for the Wrangler 3.8, including those who use 5w-20. I imagine there are lots of people on this forum who would be very interested in seeing a UOA of your oil when you drain it. That will give us a hard answer to the question of using thicker oil. I usually go through Blackstone labs and they charge $25.

 

very interesting, thanks for sharing.

keep in mind you want the oil to be thin for proper lubrication and cooling...thiker oil does flow as well when not hot... but that just part of the big oil war...

it would be cool if you send it to the lab to get an idea...this can be a Festivus Miracle

I had sent mine to the lab (it was Mobil 1), now I'm using Shell Hyper and will send it again.... then I will use the Amsoil Oil filter and will send again....Yes I'm a Mechanical Engineer... I love science...

 

So you were originally running 5w20 or 10w30?

 

Subscribed....I'm interested in long term impact

 

I haven't used 15w40 but, I use 5w30 in the winter & 10w40 in the summer. 30k on my Rubi & it runs great & doesn't use a drop of oil. No difference at all in mpg either.
5w20 is the wrong weight oil for the 3.8 in the JK.