Typical. Probably looked it up on wikipedia!! LOL.

 

Probably runs a popular Facebook group

 

You guys are such cynics!!

I love it.

 

15w40 is acceptable in a 4.0 in a hot climate, but I wouldn't run it in a cold climate.

Like stated before the 4.0 is not a diesel, and isn't really similar to a diesel AT ALL besides maybe its flat torque curve. Many diesels run 15w40 due to the high temps and shearing that an oil will see in a diesel engine. I know a 6.0 powerstroke for example is very hard on oil and will shear a 15w40 considerably due to the high pressure oil system running the fuel injectors. Many diesels are getting away from oil shearing systems like that and some even recommend 10w30 heavy duty oils over 15w40 and 5w40. Oil technology has greatly improved over the years and oils are much more resistant to breakdown.

 

Please understand I was not trying to dis' Cruiser. And, since I don't really know him, I didn't know how credible he was. It appears his credibility was long ago established.

As mentioned, being a service manager or technician doesn't really establish credibility. I was thinking the dealership in central AZ likely used 15W-40 not because it's what's best, but rather because they could buy it cheap, in bulk, and use it for everything from Neons to Ram 3500 diesel pickups.

Unfortunately, my experiences at Jeep dealerships has been less than stellar. Shortly after I bought a new 1997 XJ, the front rotors and calipers were completely shot. I lived near the ocean in Southern Virginia where multiple Jeeps were having problems with corroding rotors and calipers. Jeep even issued a recall for this problem.

I took my XJ to the dealer in Hampton, Virginia where they quickly told me my Jeep had no brake problems. Now, just that morning, I raised the front end and discovered I could not turn the wheels by hand. The calipers were stuck and the pads were seriously dragging. I asked the technician about this and he just said he connected my Cherokee to the computer and it didn't show any codes (!!!). I asked about the recall and they said it didn't apply to the Hampton Roads Virginia area.

I didn't have time to deal with this. I needed my Jeep to be driveable. I took it to a mechanic I trusted who told me had been replacing many new Jeep brakes because the factory examples had two piece rotors that were junk and the calipers sucked. He replaced both and they were fine for many years thereafter.

 

Slight correction here. Heavy diesels are specified with 40-weight oils because they need the higher shear stability and temperature tolerance. Operators choose 15w40 because synthetics are expensive. Let's not confuse the two.

6.0 PowerWank is not a great example, it's hard on everything lol.

10w30? In which engines? Not all diesels are the same...

Neons? Ram 3500? Cruiser was doing this stuff when Jeep was owned by AMC, out shortly after Chrysler showed up. I can understand your hesitation, though, as Chrysler has pulled this **** a lot. Particularly with XJs, once they were no longer under warranty, they stopped selling the actual fluids that were SUPPOSED to go in it, and just used whatever was cheap/on hand. You'll learn this if you have an AW4 transmission...

 

How cold? 2004 owners manual says 10-30 is ok for temps above zero degrees and 10-30 is PREFERRED from 32 to 100 degrees (not 5-30).
So with that in mind 15-40 should be ok for temps above 10 degrees.
Now lets talk some common sense....this same engine in the sixties was recommended to run straight 20 in winter and 30 in summer. Straight 20 is one he!! of lot thicker than a 15-40 multi-grade oil. For a 4.0 throw the idea of using 5w out the window unless you live in arctic conditions....it simply does not fit the design of this engine. It is NOT even recommended in my 2004 owners manual except for temperatures below 32 degrees! 10-30 is the recommended OEM weight. In a mild climate and high mileage engine 15-40 makes alot of sense.

BTW....the 4.0 bottom end is very similar to a diesel. True 15-40 has a higher shear but when your lugging up a trail hill that is exactly what you need.

 

Put 10w30 in your 4.0 and start it when its 20 degrees out. Watch how long it takes the oil to get to the top end. I did and now I run 5w30 in the winter. Diesel oil (known as heavy duty engine oil) has many benefits. I run it in air-cooled outdoor power equipment. I don't think it is needed in the 4.0 unless in desert climates. I've done a few UOAs with plain old Pennzoil 5w30 and 10w30 and had single digit iron wear numbers. I drive "spiritedly" and tow a trailer occasionally. The bottom end of a diesel is under a lot more stress than a low compression 4.0L is. Diesel oils also have lots of additives which protect the engine from contaminants like soot. My friend's Cummins will turn the oil black after being run only a few minutes.

Also, following recommendations from 10 years ago is somewhat silly since oils have improved immensely over the last 10 years.

 

I agree with you, especially in CT. That is why it is worthwhile to let your engine warm up. The diesel engines I have worked on also take awhile for the oil to get to the top when cold but they still have a record of longevity. Those rockers have enough residual oil left on them to adequately lubricate for several minutes. There is not a significant advantage to get worked up over. The 4.0 has had many 300+k miles stories on all types of oil including 15-40.

 

Yeah the main idea is to change the oil haha. Even then some people don't like they should and still get 300k.

 

This thread is good times.

I'm not sure what you meant when you typed that, but SAE20 is much, much, much lighter than SAE40.

The reason you had to change grades based on season was simply that viscosity-improving polymbers didn't exist. SAE10 is too thin at operating temperature to be useful in an automobile, sooo SAE20 was the best compromise for an engine that ran SAE30 in the summer.

 

We used that oil because it fit the specs for our climate per the factory manual.
I never would have skimped on oil just to make a few cents on oil changes.

 

re-read my post, I said 15-40. 15-40 cold is thinner than cold SAE40. Straight weight 40 in the old days was like molasses on a cold winter day. I used to have trouble pouring it through a funnel.....no such pour-ability problem with 15-40.

 

I used 15-40 here for years. 20*? How about 0*? I live where it gets frickin cold in the winter. A mile high with little to no cloud cover to hold the heat in overnight.
No issues.

Once again I feel compelled to post this:

Why is it that those of you who HAVEN'T done something are telling us that HAVE done something, that it doesn't work the way we have experienced by actually HAVING done it?

 

Unless they changed how they measure viscosity, 40w today would be the same as 40w from the "old days" , and the same as even "older" days