10w30 in the summer and 5w30 in the winter WHY

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My 02 Jeep 4.0 160,000 miles jeep recommends 10w30 in the summer and 5w30 in the winter why? Temp here can hit a low of -40 but average -30 for about 1-2 weeks. Summer 70-85 (seen 100 maybe 15 times in 30 years. Or we can use Arizona in the desert. If 5w flows faster at start up weather it's hot or cold outside and both oils are 30 weight at operating temperatures what advantage does 10w30 have over 5w30?. I tried an experiment winter 2016. Left 5w30 Valvoline HMSB in during the summer and found 5w30 to be quieter and (piston slap) went away faster at startup summer and winter then 10w30. The slap is gone at 210 temp quicker with 5w30. Is there some advantage to 10w30 that I am not getting? Is it all about oil shear rate between the two oils?. Are oils so much better today then 16 years ago. Would jeep change their recommendation if the oils today we're around in 2002? Does conventional shear more then synthetic or synthetic blend Thank you.
 
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It's a 4.0, it'll run (generally loudly) on just about any weight of oil. I use 10W30 winter & either 10W40 or 15W40 summer, due to low oil pressure. I can't imagine Valvoline synthetic MaxLife 5W30 couldn't handle anything a 4.0 could throw at it, short timing chain, etc.
 
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In general, a 10W will have a thicker base oil with less viscosity index improved (VII) needed to be a 30 weight at temp. This makes them better, in general, in high temp, high shear environments over a 5W.
 
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Originally Posted By: 1JZ_E46
In general, a 10W will have a thicker base oil with less viscosity index improved (VII) needed to be a 30 weight at temp. This makes them better, in general, in high temp, high shear environments over a 5W.
What would be a good indicator for the OP? The vis @ 100 C from the VOA?
 
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Originally Posted By: littleant
. Would jeep change their recommendation if the oils today we're around in 2002? Does conventional shear more then synthetic or synthetic blend Thank you.
My 2008 Chev 6.0 called for 5w30 year round. I ran full synthetic. It has 160,000 miles and does not use a drop.
 
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Originally Posted By: Snagglefoot
Originally Posted By: littleant
. Would jeep change their recommendation if the oils today we're around in 2002? Does conventional shear more then synthetic or synthetic blend Thank you.
My 2008 Chev 6.0 called for 5w30 year round. I ran full synthetic. It has 160,000 miles and does not use a drop.
I realize HTHS is for any surface under high shear, but couldn't the main bearings be under yet higher shear than the cylinder walls? Meaning, I'm wondering if HTHS matters more to bearings than to cylinder wall lubrication.
 

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The last time I saw viscosity vs temperature curves for different grades, I noticed 5W- buys you around 15°F over the 10W- viscosity. In other words, 10W at 50°F has the same viscosity as 5W at 35°F at startup. Not a whole lot of difference considering the temperature swings we get from one week to next. For perspective, contrast this with the fact that many manufacturers okay 5W-30 for use over a 100°F ambient temperature range.
 
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My take is that I might get an oil with a lower NOACK loss if I buy a 10W30 from a given line of oil for summer use rather than a 5W30 (look at the Amsoil SS PDS as an example), but it can be very hard to get real information that will prove this is the case. I'm just glad that SN Plus is going to include some 10W30s, that grade was not part of the dexos1 Gen 2 specification (or dexos2 for that matter).
 

littleant

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Snagglefoot I looked at a bunch of voa on the forum and it appears Valvoline Castrol HM SB has The highest vis @ 100 C. Downloaded a bunch of pdf's to compare all HM oils (Val-pennzoil -QS) seems Valvoline has SB and full synthetic HM. Pennzoil has conventional and full synthetic. Would go with the thickest 5w30 highest vis @ 100 C
 
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No one re writes oil recommendations for 2002 Jeeps 16 years down the road. Oil is different/better today. You would be fine running 5W-30 oil year round in your Jeep. My 1994 Wrangler has lived on that oil for the last 12 or so years.
 
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Originally Posted By: Snagglefoot
Originally Posted By: 1JZ_E46
In general, a 10W will have a thicker base oil with less viscosity index improved (VII) needed to be a 30 weight at temp. This makes them better, in general, in high temp, high shear environments over a 5W.
What would be a good indicator for the OP? The vis @ 100 C from the VOA?
HTHS is a better indicator of base oil thickness. For example, many 10W-30s have a slightly higher HTHS for the same KV100 figure, which probably means less VII was used to get to the same KV100 figure. VII flattens our (temporary shear) in HTHS test. The HTHS is what matters. KV100 is sort of a meaningless number.
 
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I think M1 HM 10w30 with it's 3.5 HTHS is the perfect oil for these jeeps but that's just my opinion.
 
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I have a slight weep at the rear main seal on my 4.0 XJ. I like the higher weight to reduce the week as well as avoiding shear. I tend to use the cheapest synthetic xW30 or xW40 I can find and change out at 5k. The 4.0 runs pretty hot so can sludge oil. I also use a Fram Ultra XG8A oversized filter and swap every 3 oil changes.
 
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Originally Posted By: 1JZ_E46
In general, a 10W will have a thicker base oil with less viscosity index improved (VII) needed to be a 30 weight at temp. This makes them better, in general, in high temp, high shear environments over a 5W.
+1 smile
 
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Originally Posted By: littleant
Jeepwj19 and svhanc you both use the longer filter and 5w30 synthetic oil just different brands. Do either of you have any piston slap.
I don't know if I have piston slap or lifter tick, but ever since I've owned (60k miles accrued) it has always ticked very loud on every cold start no matter the outside temperature. I've come to accept it smile. And no, I don't use 5w30. I use 10w30.
 
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I've run 10-30 winter and 10-40 summer for years , seems to do just fine in anything I've owned
 
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