I don't usually do this but this time around, I'm going to second the use of Mobil 1 in these engines.
I've never worried too much about the viscosity numbers. The older ones called for 5w30 and the newer ones called for 5w20. The engine as far as I can tell did not change. So 0w20 5w20 0w30 5w30 10w30.
A previous Dodge engine a friend of mine had needed a quart of something thicker. It had an actual pressure gauge and it had a cold start clatter on winter mornings. This took care of the clatter and increased the oil pressure a little. So the first time I heard mine clatter on a cold morning start, I went and asked if I needed to do this with the 3.7L and in doing that, I have seen the oil passages on these years ago. I personally would not put anything thicker than __w30 in these engines, nor would I ever put cheap crap in it that might varnish or gum up worse. Just would not do it. I've seen what happens and it is not pretty.
I usually go with the intention of buying Mobil 1 5w30 but if it is sold out I just reach for one of the others. I assume the 5w20 is for fuel economy for the manufacturer where a 0.001 MPG increase matters. In my useage, I have never been able to tell an MPG difference. So I don't usually get the 5w20 or 0w20. It don't get all that cold here either.
Anyways, in my opinion this engine likes the Mobil 1 oil. I've ran the standard, the EP, the high mileage, the high mileage EP because again I usually shoot for the 5w30 and they usually have one of those in 5w30. Seems to like any of it fine.
I did however switch over to high mileage oil because I started leaking. I did not know at the time it was because I was having weird PCV valve issues. Prior to that I had never tried any of it. It of course did not slow the leaking because it was pressure pushing it out. After resolving the PCV issue it slowed the leaking to weeping. And it has kept on weeping. Right now it has the black bottle Valvoline Synthetic high mileage for over 150k in it because someone talked me into trying it saying that it would stop the weeping. I will be draining that out as soon as I get a chance because I can absolutely tell a difference. It just don't sound good. I don't know what it is, but I can detect a noise at idle sometimes that I have never heard before.
Anyways, Mobil 1 for the win for me. I try to buy it on sale and usually save most or all of the extra coin it costs. It's been working great for me for almost 240k in the Jeep. Over 330k in the truck before it. My Acura Turbo specs Mobil 1 5w30 only on the oil cap. The Mazda gets it too. Water outlet just broke on it like a month ago. No doubt in my mind the oil saved the engine. My mowers and ATV's also get their respective Mobil 1.
I am not some fanboy. It just works for me. It's saved my ATV racing engines several times when I had issues that should have fried them. I've torn those engines down and they look brand new inside still. I have one that should be rebuilt at minimum twice a season. I raced it 7 seasons, plus recreational riding hours. It still has the same compression it had when it was originally broken in. I probably should tear it down this winter and replace the crank, rod, piston, valves and springs, just for fear of metal fatigue... in other words to prevent a catastrophic failure like a broken crank, rod, piston, valve coming through the bottom, side, or top of the motor, just from fatigue, because at this point that is what I know is going to happen before it ever generates enough wear to loose an compression. And it is much cheaper to prevent than turn it into a basket case.
