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Discussion Starter #1
Have a 2002 Grand Cherokee w/4.0L straight six engine.

Manual recommends 10w-30 oil for 0 deg and up and 5w-30 for 32 deg and lower. At this time of year temps are likely to go lower than 0 deg before the next change, but it's also going to be over 32 deg much of the time. I always have this dilemma at this time of year.

Have the recommendations changed at all over the past ten yrs? Can I just use one or the other year-round? If not, how do I solve the dilemma?
 

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Welcome to Allpar. As long as your engine is in good mechanical condition, you should be fine with 5W-30 year round. The slightly lighter viscosity may also afford you slightly better fuel economy. Lighter grades are great for colder temperatures.
The heavier grade 10W-30 0r 10W-40 may be good for reducing oil consumption or engine noise, if that is an issue.
 

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The chart in the OM is where I got the range I quoted. It shows a bar starting from 0 deg to > for 10w-30. The second bar starts at 32 deg and goes down to
 

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KOG
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I've used 5W-30 in all of my gas engines for a long time, but the 4.0 requires 10W-30 for warranty in my climate so I use it as I have a lifetime powertrain warranty. I think it would be better to use 5W-30, but what do I know? My engines usually don't last a great deal longer than 300K or at least I've sold the car by then.
 

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Theres a lot of people running HDEO xW-40 in these engines with good results.
 

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During the winter if I started a car and drove a couple of miles to the store occasionally and the temperature hovered around -20F I would be sorely tempted to switch to 5W-20 or even a synthetic rated 0W-20 Next time you're bored in mid-winter and have nothing better to do, put a bottle of 0W-20, and 10W-30 outside in sub zero F weather and in the morning dribble a little out and see how thin they are or aren't. Made a believer out of me.
 

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KOG
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The problem remains that you aren't dealing with an engine when it's under warranty. You're dealing with lawyers who wish to void your warranty if they can find an excuse. You must use the specified oil or you're done.
 

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Discussion Starter #9
Well, the engine in question in the OP is long out of warranty.

The oil temp range in the OM is really limited. 10w-30 for everything above 0 deg. seems reasonable. However, winter in MI certainly goes below 0 quite frequently and by quite a bit. The range for 5w-30 for 32 deg and lower seems to be awfully limited. It will surely go above 32 deg just as frequently.

Will 5w-30 be safe enough to use year-round... or not?
 

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Virginia Gentleman
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Will 5w-30 be safe enough to use year-round... or not?
You'll be fine. Though it's not the same engine, I had three 2.5's that logged over 800K miles between them and all I used was 5w-30 for the entire "life" of each engine - year round. Now where I live (eastern VA) does not get below 0*F often - coldest we usually get is mid teens, but we do get over 100*F frequently in the summer.

Your vehicle is a 2002 and unless you have a lifetime extended warranty (or do you?), there are no warranty issues.
 

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KOG
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Out of warranty I'd use 5W-30 or even 5W-40 such as Rotella Synthetic.
 

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Albeit my 3.0 has only 70,000 miles, I found it interesting that it did not complain driving through very hot weather coming out of México. I use 5W/30 and all the thermometers read above 120 degrees Fahrenheit for over 200 miles distance. The one is Lukeville AZ, at the border patrol station read 122F. Sheesh, the thermometer in Laughlin Nevada read 101F at midnight. I guess the newer oils are better than the stuff we had fifty years ago. I would have thought I needed straight 40 for temperatures like that.
 

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Virginia Gentleman
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Today's oils are far better than they were just five years ago. Why do you think the max oil change interval is up to 8,000 miles on some new models.?
 

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KOG
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Perhaps they got a clue. I've been on annual changes for the older 3.3s for 20 years. Sometimes over 15K. Engines clean and fine at up to 250K miles.
 

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a 0W- 20 would at lower temperatures behave like a 0W- 40 and
a 0W-40 would behave like a 15W- 40 at operating temps.
Note that a 0W- 20 would be avfully thin in an engine designed for a xW-40 at operating temperatures.
Also noteworthy is a number called VI or viscosity index, the higher the number is the change of viscosity decreases
due to temperature changes- ok good just get the highest VI or ?
Well this opens next can of worms.
Every baseoil has a natural VI number wich the blender modify or just use, the natural value is wery stable and wont change unless
the oil is severly mis used- like overheating, extreme soot loading, extreme oci´s etc.
If the base oil doesent have a correct VI theres ways to fix it by using VI improvers, these have a tendency of behaving like a "Thickener"
when the oil gets hot..sounds good doesent it..well it usually doesent matter but these adds get worn out with use and
here comes the great debate about syn vs dino.
Very simplified, a 5W-40 syn usually doesent need any VI improvers since the base oil already is a 5W-40 but
the dino one needs to start with a baseoil that is say 5W-20 and improved with VI improvers so theres not as much robustness and wear tolerancens in the dino as the syn.
Note however that oil chemistry has gone a long way and theres a diminising line between dino´s and syns with some very high performing group 3
oils like most hdeo´s wich are severly hydro cracked dino basestock- one could argue if these are dino´s or syns.
Conclusion...choose the lower number for your lowest temperature and the higher by the book or like me a grade higher (30 -40).
I use a good hdeo 10W-40 in eveything due to the fact that i get it in 25 liter cans for a very good price compared to passcar oil.
Yes i know now every one will yell at me because of the mds in hemis...well these engines are not normal, the exception of the rule..or?
 

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Discussion Starter #16
It would be a bit easier to stock just one oil for both vehicles, but it's not a big deal. Our Sebring recommends 5w-30 as the 'preferred' oil. !0w-30 is the 'preferred' oil for the Jeep. I have no problem using It.
It just seems odd that the 5w-30 has such a limited temp range for the Jeep, considering that it's the preferred oil for many other engines. That same oil chart also applies to the 4.7HO engine. Doesn't seem like there are many places where the temps stay below 32 for the length of an oil change.
Considering that the OM recommendation is over 10 years old, is there a contact at Chrysler that would know if that chart is out-dated or modified?
 
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