Someone mentioned the corvette manual saying to changing from 15w30 to 15w50 for track use. That's strictly because during track use, the engine is operating at much higher speeds, so the oil temperature and pressures are going to be a lot higher than when you're driving to the golf course. The 15w50 oil during track conditions will have the same viscosity as the 15w30 oil will have during normal driving.
That was me and that is NOT why GM recommends...
They recommend 5w 30
But for track use they recommend 15w50
I point this out simply because....the question (silly question like all these oil thread questions) is would a 20w50/60 hurt the Jeep engine.
The Corvette engine is a fairly expensive piece of equipment...no? It's warranted, no?
Yet GM RECOMMENDS using this "OH MY DEAR LORD 50w is way too thick of oil"....oil.
There are two real reasons they won't commit to running 15w50 all the time. (Don't let anyone bullshit you. I talk to these reps all the time. They chuckle at these grand daddy said to use oil debates)
GM has no control over people who operate their vehicles in extreme cold temps. They can recommend when the temperature reaches 15°(F) or lower to allow an engine to warm up before putting a load on it (driving) but that doesn't mean they will. Moreover most people won't operate their Vette if it's extra cold 0° but there can be some that will...
Thus the need to protect themselves...
Second reason is a monster.
A big bad fire breathing monster called the EPA.
The EPA might be the most powerful organization in the world. FBI,CIA,BATF(E) included...the EPA possibly has the biggest **** of them all.
They put insanely immense pressure on these mfg's to comply/appease.
A thinner oil "can possibly" do two things. Eek out better MPG...and again ...("possibly") provide longer catalytic converter life.
The EPA doesn't need concrete evidence. If they think something "might" or "possibly" add MPG or pro long the catalyst life and or efficiency of it...
Well you better just etch that shit in the Moses stones then because it's fact.
The ultimate point is this...
A Jeep engine is not some high tech expensive piece of equipment. Matter of fact it's much closer to an industrial engine, tractor engine than a modern day passenger car engine. They were sloppy coming off the carrier.
Ever see the inside of an industrial engine like that after spending 50 years of running conventional SAE 40? Prolonged hours of idle speed....on/off...under heavy loads...etc,etc
Ever see one inside that wasn't maintained?
And that's the key. All these oil horror stories by that weird Tom Hanks like neighbor guy (everybody has that neighbor)
Brand X doesn't sludge more than brand Y... brand A won't blow your engine...
But most importantly what you never actually know is
N
E
G
L
E
C
T
Neglect will kill an engine. Period!
A 50/60 weight oil keeping it changed won't hurt that 4.0 one tiny bit. (Provided this isn't arctic temperatures)
Not one bit!