Same engine, different SAE grades over time?

[Six_in_a_row]

I understand that car brands sold internationally can have different SAE grades recommended for different markets. Several posts have explored this in detail.

I want to ask why this is true over several model years in North America, or at least in the United States. It would appear that a previous year’s recommendation would work for a more recent year. I can’t believe that drastic engineering changes to internal dimensions, clearances, and components would make sense or justify an SAE grade change. That would be much more than tightening tolerances, which is not (I believe) part of my question.

Please allow me to use as examples the Jeep 4.Ol and Jeep 3.7l sold over several model years. I found this data on the Jeep web site in the “owners” section that allows you to download owners manuals for previous years. This is not a criticism of Chrysler, but rather a statement of my bewilderment.


Jeep 4.0l

1999 Cherokee, over 0F and above 100F 10w-30 (preferred)
below 32F 5w30,

1999 Cherokee from my shop manual, over 0F and above 100F 10w-30 (preferred), below -20F to 100F 5w30
(Is this an editing error?)

2004 Wrangler, below 32F 5w30,
over 0F and above 100F 10w-30 (preferred)

2004 Grand Cherokee, below 32F 5w30,
over 0F and above 100F 10w-30 (preferred)

2005 Wrangler, below 32F 5w30
over 0F and above 100F 10w-30 (preferred)

2006 Wrangler, 10w-30 for all temperatures
(There is no mention of any other SAE grade. Yup, this is not a mistake!)



Jeep 3.7l

2004 Liberty, below -20F to 100F 5w30 (preferred),
0F to above 100F 10w-30

2005 -2006 Liberty, 5w30 for all temperatures

2005 Grand Cherokee, 5w30 for all temperatures

2007 through 2010 Liberty, Cherokee, and Commander; 5w-20 for all temperatures

* * *

Can we go back in time for a SAE grade recommendation?

Likewise, can we go forward in time for a SAE grade recommendation?

Thanks for your help!

 

[Michael_P]

Or what about the same engine sold in other parts of the world with similar climates with different oil requirements?

Maybe I'll try 5w20 in my boat even though it calls for 30-40wt. It is a Chevy 8.1 after all. (Just kidding)


FWIW, I wonder if those Jeeps with the heavier oil recommendations have worse EPA fuel economy estimates than their later model siblings.

The Ford Modulars have stayed the same clearance wise, but have also had different oil weight recommendations depending on year and country. They seem to run well on a variety of weights at the same temp.

No questions or answers, just mentioning.

 

[Hokiefyd]

This has long confused me also, but since I don't have any engineering knowledge of the data from which the recommendations were made, I tend to stay away from conjecturing a guess. Because that's all it'd be: a guess.

My former 2003 Grand Caravan took 5w30 oil. My current 2007 Chrysler Town & Country takes 5W-20 oil. Working knowledge is that it's the "same" engine, but nobody has any real knowledge if anything's different inside. All we have is a change in the recommended viscosity grade. A million and one persons will blame the EPA and CAFE, yet the EPA's fuel economy estimates didn't change, so I'm not sure what motive Chrysler would have to go to a 5W-20 oil when many of their current vehicles continue to use 5w30 oils (standardization of bulk lubricant inventory seems unlikely to me). In addition, the 4.0L V-6 engine in their newer minivans requires a 10W-30. Not even a 5w30! If CAFE is the reason for the switch to 5W-20 on the 3.3L/3.8L engines, why not also the 4.0L engine? Surely, there's an engineering reason behind this. I just don't know it.

 

[mechtech2]

They could not spec an oil that was not existing yet.
5-20s are proven tough, but needed to be developed and tested.

As to 10-30 vs. 5-30, they should be very similar when hot. the 5-30 may even be thicker, depending on which one you get.

The '5' first number is better than a 10, because it flows better when cold. Maybe they conservatively thought that the `10-30 was more stable in construction.
This is also shown to be not a problem.

 

[Hokiefyd]

Yeah, I can't figure why they spec'd the 10W-30 vs. a 5w30, for the 4.0L V-6 engines. Overall, it looks like the 10W-30 tends to be a bit more stable. Maybe that engine is a monster on oil. It's related to the 3.5L engine as well.

 

[Six_in_a_row]

Originally Posted By: Michael_P
Or what about the same engine sold in other parts of the world with similar climates with different oil requirements?

Maybe I'll try 5w20 in my boat even though it calls for 30-40wt. It is a Chevy 8.1 after all. (Just kidding)


FWIW, I wonder if those Jeeps with the heavier oil recommendations have worse EPA fuel economy estimates than their later model siblings.

The Ford Modulars have stayed the same clearance wise, but have also had different oil weight recommendations depending on year and country. They seem to run well on a variety of weights at the same temp.

No questions or answers, just mentioning.


Michael,

There can be a big difference between 10w-30 and 5w-20 in the the Jeep examples. I see your analogy with proposing to run 5w-20 in your hard working Chevy boat engine!

 

[Six_in_a_row]

Originally Posted By: Jason Adcock
This has long confused me also, but since I don't have any engineering knowledge of the data from which the recommendations were made, I tend to stay away from conjecturing a guess. Because that's all it'd be: a guess.

...snip...


Jason,

I'm glad to discover that there are others out there who are curious! I for one would be grateful if an active auto engineer would carefully jump in here!

 

[Johnny248]

you guys realize that engine internals actually change over the years and with different models right? For same model year 4.0 Cherokee has different pistons than the 4.0 in the Grand Cherokee. So I'm sure that sometimes they spec oil for different reasons, but it also does not mean that they don't change oil passages, or tolerances or materials, or other internal engine parts.

 

[demarpaint]

Originally Posted By: Johnny248
you guys realize that engine internals actually change over the years and with different models right? For same model year 4.0 Cherokee has different pistons than the 4.0 in the Grand Cherokee. So I'm sure that sometimes they spec oil for different reasons, but it also does not mean that they don't change oil passages, or tolerances or materials, or other internal engine parts.


Good points, engines sometimes have slight changes internally and externally from one model year to another, even though the engine is the same. Could be as simple as changing the threads for the oil filter mount [no effect on oil viscosity], to a better piston or ring, different valve guide, bearings, etc, etc, etc. So oil specs can change. It could also be a change in oil pumps.

 

[OilNerd]

True, but sometimes the same engine, same model in different model years is spec.'d differently. For example, the Buick LeSabre with a GM 3800 Series 2 motor - 10w30 preferred in '02 and 5w30 preferred in '04.

 

[beast3300]

Originally Posted By: OilNerd
True, but sometimes the same engine, same model in different model years is spec.'d differently. For example, the Buick LeSabre with a GM 3800 Series 2 motor - 10w30 preferred in '02 and 5w30 preferred in '04.


The oil pressure relief spring was changed in 04 to push higher oil pressure. I used 5w30 all of 2009 in my Regal with no problem (including track duty).

 

[Hokiefyd]

Originally Posted By: Johnny248
you guys realize that engine internals actually change over the years and with different models right? For same model year 4.0 Cherokee has different pistons than the 4.0 in the Grand Cherokee. So I'm sure that sometimes they spec oil for different reasons, but it also does not mean that they don't change oil passages, or tolerances or materials, or other internal engine parts.


Yes, absolutely. And this is my point. Most people default to the standard "CAFE" reasoning, when there's often a very valid, and engineering-based reason behind the change in viscosity grade spec.

Problem is, we typically don't know what that reason is. For example, what changed with Chrysler's minivan engines between 2004 and 2005 to make 5W-20 the only recommended grade in 2005 and beyond? I dunno.

 

[OilNerd]

Originally Posted By: Jason Adcock

Yes, absolutely. And this is my point. Most people default to the standard "CAFE" reasoning, when there's often a very valid, and engineering-based reason behind the change in viscosity grade spec.

Problem is, we typically don't know what that reason is. For example, what changed with Chrysler's minivan engines between 2004 and 2005 to make 5W-20 the only recommended grade in 2005 and beyond? I dunno.


Sure, but because of the CAFE rules, we don't know if it's new engineering, just for CAFE purposes, or a bit of both. From what I understand of CAFE, whatever oil grade they spec. for CAFE testing, automatically becomes the "preferred" grade.

If a different grade is spec.'d for just a minute improvement in MPG and one grade is as good as another in the engine, it would be nice to know that.