I recently purchased an 04' Hemi Ram. Two years ago I owned an 05' Hemi. The 05' uses 5w20 oil and the 04' calls for 5w30. Can anyone explain why the two different years call for different weight oils? Does anybody have any tech info about the two different engines as to why the change?

 

Wow, that is strange. I got a buddy with a 04 and his calls for 5w-20.

 

It's marked on the oil cap and it says it plain as day in the owners manual.

 

You are correct, and I've asked that question many times, other than a couple PCM code changes, the '04 and '05s are basically identical. Nobody, including Chrysler service managers and Mopar performance shops guys have really given me an answer on it.

I have an '04 and always ran 5w-30 until I went to a 180* thermostat then went to 5w-20, figured the cooler operating temp would like the slightly thinner oil, plus, since it was recommended for the '05s, would do no harm.
I even had a service manager swear they didn't go to they went to MDS in the '06s, but I made him look it up and he could only scratch his head and shrug his shoulders...

 

I run them both on my truck. 30 in summer, mix in fall and spring, 20 in winter.

 

I'm not disputing you man, just saying I know an 04 that has 5w-20 on the oil cap, I saw it myself.But either way I don't think either oil would hurt anything.

 

They change the recommended weight randomly because they arent chemical engineers nor fluid dynamics scientists. They really have no clue what the optimal oil for your engine may be.

However, here is a nice write up from a guy who does. A very good read.

http://webpages.charter.net/bosorio/MotorOil.doc

 

GM a few years back went to the lower weight oil to improve the gas mileage in the EPA testing. The thought was a tenth here and a tenth there and you started to pick up MPGs. The choice of tires was influenced by the rolling resistence and so on. Similar to xfeejayx, I use 5W-30 in summer, 5W-20 winter but do not mess around in Fall or Spring. My mileage is down to 10-12K a year, so I am only changing the oil twice a year.

 

yea my mileage is double that. I started picking up oil on sale the last few times, and of course it's never on 7 quarts worth. So I just dump in whatever I had of the last batch then the new 30/20 depending on the season.

 

It's a mileage thing. The thinner oil produces a bit less drag.