Jeep oil viscosity chart... riddle me this?

[Poobank]

Looking at my 2001 jeep GC owners manual I'm wondering about this viscosity chart. Why would the 5w30 not cover the same hot side as the 10w30 for the 4L but not the 4.7L? Just don't make sense to me. Maybe I'm missing something, can you guys help me out with this?

 

[CT8]

Cafe

 

[HoosierJeeper]

I have a 4.0 XJ and a 3.7 Liberty (which the 3.7 is a 4.7 sans 2 cylinders)...5w30 in both. For the XJ I'll switch back to 10W30. The Lib has always had 5W30. I'm totally speculating here about why 5W30 isn't "recommended" for summer in the 4.0, but I'm guessing it's because 5W30 could be more prone to shearing and the 10W30 is less prone and 10w works fine for warmer starting. Since 5W30 is more prone to shearing (I think?) and the 4.0 needs a thicker oil, that's probably they spec 10W30 for warmer temps whereas 5W30 might be become too thin.

I'm just guessing on my limited oil knowledge, I hope someone can answer this!

 

[901Memphis]

Sometimes the 10w30 is actually thicker than the 5w30 if we look at HTHS viscosity. This is less of a problem with synthetics, since they shear less.


I will tell you I have been bewildered by these engines tracking used oil analysis over time, some mystical thing happens to them when they run 5w30 and the wear tends to be higher. It doesn't make sense but I've noticed it.

 

[delirious]

Originally Posted By: HoosierJeeper
I have a 4.0 XJ and a 3.7 Liberty (which the 3.7 is a 4.7 sans 2 cylinders)...5w30 in both. For the XJ I'll switch back to 10W30. The Lib has always had 5W30. I'm totally speculating here about why 5W30 isn't "recommended" for summer in the 4.0, but I'm guessing it's because 5W30 could be more prone to shearing and the 10W30 is less prone and 10w works fine for warmer starting. Since 5W30 is more prone to shearing (I think?) and the 4.0 needs a thicker oil, that's probably they spec 10W30 for warmer temps whereas 5W30 might be become too thin.

I'm just guessing on my limited oil knowledge, I hope someone can answer this!


In my opinion I think shearing is the major contributor for the 4.0 getting the 10w30 as the biggest nod.

I really love my WJ OP and I think you'll like yours. They are still a Chrysler product so just be aware but they are one of the last few vehicles (imo) that are easy to work on vs 2005 and onward.

CAFE is another reason for these oil choices. I believe another poster on here, his is dlundblad, posted that 4.0s were spec'd a 40 weight in Europe.

If you want to stay on the safe side follow the owners manual. Either jeep gets an xW-30 so you have plenty of options.

For the 4.7 I think any xW-30 would be fine.

As for the 4.0, it is of my belief that they run better on oils with a higher HT/HS. Thicker xW-30s work great and so do 40 weights. My 4.0 so far has been smoothest on 40 weights but also runs really great with thicker 30weights.

 

[Nick1994]

The 4.0L tends to shear 5w30 oils easier, so unless you really need the 5w for cold starting, you might as well use a 10w30.

From what I hear, 5w30 oils are more shear stable today though than they were back in the day

 

[delirious]

Originally Posted By: 901Memphis

I will tell you I have been bewildered by these engines tracking used oil analysis over time, some mystical thing happens to them when they run 5w30 and the wear tends to be higher. It doesn't make sense but I've noticed it.


I have seen those as well and it gets me worried at times, especially now. I kind of self-justify it by saying it's winter time, which I admit doesn't have any sound reasoning at all :]

 

[Poobank]

After reading the discussion leaning towards the idea that 5w shears more and maybe the ol 4l was pre increased cafe standards. I'm actually running 5w40 in my 4L. My oil pressure seems to drop on the lower side when the oil is hot and motor is worked. Either from a lazy oil pump or clearances or just a messed up electric fan lol.

 

[dlundblad]

In England at least, the 4.0 gets 5w40 or 15w40 depending on temperatures.

The 40 weight was a good choice.

 

[Alex_V]

The 4.0L is an inline six with a flat-tappet cam designed in the 80's by AMC. The 4.7 is an overhead cam (assuming roller) V8 designed by Chrysler in the late 90's. Two substantially different designs, just making it into the same vehicle because Chrysler owned Jeep.

 

[dlundblad]

Originally Posted By: JeepWJ19
Originally Posted By: HoosierJeeper
I have a 4.0 XJ and a 3.7 Liberty (which the 3.7 is a 4.7 sans 2 cylinders)...5w30 in both. For the XJ I'll switch back to 10W30. The Lib has always had 5W30. I'm totally speculating here about why 5W30 isn't "recommended" for summer in the 4.0, but I'm guessing it's because 5W30 could be more prone to shearing and the 10W30 is less prone and 10w works fine for warmer starting. Since 5W30 is more prone to shearing (I think?) and the 4.0 needs a thicker oil, that's probably they spec 10W30 for warmer temps whereas 5W30 might be become too thin.

I'm just guessing on my limited oil knowledge, I hope someone can answer this!


In my opinion I think shearing is the major contributor for the 4.0 getting the 10w30 as the biggest nod.

I really love my WJ OP and I think you'll like yours. They are still a Chrysler product so just be aware but they are one of the last few vehicles (imo) that are easy to work on vs 2005 and onward.

CAFE is another reason for these oil choices. I believe another poster on here, his is dlundblad, posted that 4.0s were spec'd a 40 weight in Europe.

If you want to stay on the safe side follow the owners manual. Either jeep gets an xW-30 so you have plenty of options.

For the 4.7 I think any xW-30 would be fine.

As for the 4.0, it is of my belief that they run better on oils with a higher HT/HS. Thicker xW-30s work great and so do 40 weights. My 4.0 so far has been smoothest on 40 weights but also runs really great with thicker 30weights.


You beat me to it. Lol.

 

[delirious]

Originally Posted By: dlundblad


You beat me to it. Lol.


Yes but at least I give you credit where credit is due, my friend :]

 

[aquariuscsm]

Alot of cars still spec 10W30. I was in a Honda dealership the other day and they have a current lube chart in the parts dept. The S2000 still specs 10W30 in warm-hot climates. There was a Nissan tsb awhile back that said "All Nissan vehicles use 5W30,except 300ZX* (*refer to owner's manual). *Which states 5W30 to be used only at 59F and below,not when racing,and/or driving at extended high speeds. 16F and above,use 10W30,10W40,15W50,and 20W50. Every spun bearing incident I've seen in cars like mine were always running 0W30 or 5W30,which is forbidden in the Z32 fsm,in the conditions they were being used. Me,I have no desire to try to out think the Nissan engineers,as I feel they are a teeny tiny bit smarter than me

My car sheared Synerlec RP 20W50 down to a 10W40 within 3000 miles (sheared it down into the 14 range,which is "thin" for a 10W40,which some are in the 15+ range).

If your car specs 10W,that's what I'd stay with.

 

[Pagophilus]

You're all reading this wrong, though I admit it's easy to do. The chart does NOT indicate that 5w30 doesn't cover the same hot side as 10w30.

The end of the range is specified by the pointy end. The flat end is not where the range ends. It's where they stopped drawing the line. In other words, 5w30 covers from around -30C to 0C, and then it's the same as the 10w30 oil.

All these charts work the same way. Some of these ranges only specify one side of the range but don't indicate how far the other side extends. Yes, confusing to the uninitiated.

 

[SR5]

Originally Posted By: dlundblad
In England at least, the 4.0 gets 5w40 or 15w40 depending on temperatures.

The 40 weight was a good choice.


They feed the 4.0L six 40 weight oil in Oz too.
15W40 mineral, 10W40 semi-synthetic or 5W40 full synthetic.

 

[Ducked]

Originally Posted By: 901Memphis
Sometimes the 10w30 is actually thicker than the 5w30 if we look at HTHS viscosity. This is less of a problem with synthetics, since they shear less.


I will tell you I have been bewildered by these engines tracking used oil analysis over time, some mystical thing happens to them when they run 5w30 and the wear tends to be higher. It doesn't make sense but I've noticed it.


You SEEM to be saying that "thinner" oil gives more wear, and that this doesn't make sense.

This doesn't seem to make sense.

 

[KCJeep]

I think some on this thread have the 5w confused with weight which is not correct, that is the winter starting indicator.

Regarding 5w30's in the 4.0, I have used them for short runs in the winter with no issues, but I am firmly convinced the 4.0 thrives on thick 30's or 40's on the thin side. You can go thicker but frankly I think it is overkill and pointless. Numerous used oil analysis have shown the 4.0 will shear a 5w30 down a good bit in short order. Not really a good thing since the 4.0 does better on thicker oil. My best used oil analysis ever was on Pennzoil 10w40. Currently running 0w40 this winter, best of both worlds!