Synthetic 15w-40 vs 5w-40

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13
Location
DC Metro
It used to be that in that if you ran conventional you ran 15w-40 and if you ran synthetic then there was no 15w-40, so you ran 5w-40. Typically for me, it would be Rotella, T4 vs T6 (since you don't know how much of each there is in a synthetic blend if I felt like saving some money I would get a gallon of one and 2 of the other and mix them rather than buy the T5).

Lately, I've noticed 15w-40 T6 and other full synthetics showing up and as I'm about due or an oil change I've been wondering if there is an advantage in using 15w-40 over 5w-40 assuming that they are both the same type and brand oil (looks like some of the same in showing up in the other brands like Delvac...)? Since at operating temp they should both be about the same, but the 5W should be better on cold starts I'm wondering why Shell and others are suddenly coming out with a 15W40 synthetic. I know the conventional answer is that you should run as tight a "spread" as possible for your temp range because it takes more viscosity modifiers to make a larger spread which makes the oil more susceptible to shear damage, but I thought that the way synthetics are made that isn't an issue?

FWIW, this is in a 5.9 Cummins Ram that is likely to see temps 0-100*F during the next oil change interval, though 90% of that will likely be in the 50-90* range (here in the DC metro area we will get cold nights getting down into the 0-5* range once or twice a year, but we've had something like 30something days straight getting over 90* so far this summer and almost 50 that it hasn't gotten below 70*F)
 
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2,560
Location
wv
" I'm wondering why Shell and others are suddenly coming out with a 15W40 synthetic. "

Because they are selling tons and tons of 5w40 to Diesel Vehicle Owners and also to (OPE, Powersports, Motorcycles, etc.)


" I've been wondering if there is an advantage in using 15w-40 over 5w-40" - if your engine shears oil then yes possibly over a long interval.
 
Messages
246
Location
Iowa
my take is marketing, 15W40 is a common HDEO viscosity so people associate that with better (synthetic and 15W40 = (y)).

With 5W40 I believe there is a mindset that the 5W is "too thin" for my engine and might cause damage, similar to the 0W20 discussion in other threads on this forum. I would hazard a guess that most oil consumers don't understand what a multi weight oil even means.

For your application I'd evaluate what is your end goal. If you aren't going to extend the OCI then why switch? There are plenty of 5.9's running around out there with hundred's of thousands of miles on them running conventional 15W40. FWIW, my 6.7L is good on 15W40 down to 0F but generally sits in my attached garage overnight and I usually plug it in because I like the immediate heat on a cold morning.
 
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172
Location
Brazil
I can get a 5W40 SN A3/B4, 229.5, A40 for the same price of the conventional 15W40 SL E7, 228.3, that i'm using on my 94 engine. The only reason why i am still using the HDEO is that i think the higher HTHS and base oil viscosity will give me better oil pressure and protection. With an OCI of 6 months and 2k miles and living in temperatures above 60 °F, i don't see the reason to change on an engine that is working great with conventional oil for the past 26 years.

But if we had the 15W40 synthetic (not avaible here yet) i would love to try it out, especially if the price was similar.
 
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3,858
Location
Slovenia EU
I had 5w40 (Elf nf 900 5w40) in my LC....the point is that Landcruiser has small "gearbox" on that particular engine....which drives its injector pump...that set ob gears is lubricated with its engine oil...and because of that is a great oil shredder...

It consumed 5w40 like crazy....but 10W-40 HDEO is constantly @ full mark ;)
 
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1,653
Location
Caldwell Idaho
5W-40 all things equal is inferior to a 15W-40 due to the thinner base oil blend and the viscosity improvers needed. That being said and as mentioned the 5W wil lbe better below 0*f for cold pumpability. I use 5W-40 in my tractor because I change oil once a year and I want the cold pumping in the winter if there is a cold spell and the temps drop well below freezing and I need to clear the road or something..
 
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221
Location
SC Coast
i know when I had my 6.0 Powerstroke the 5w-40 helped alot with the cold starts and "stiction" issue in injectors. the 15w oil would normally smoke more on start up and take a minute or 2 to idle smoothly.
 
Approvals.

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Messages
646
Location
South Carolina
I had 5w40 (Elf nf 900 5w40) in my LC....the point is that Landcruiser has small "gearbox" on that particular engine....which drives its injector pump...that set ob gears is lubricated with its engine oil...and because of that is a great oil shredder...

It consumed 5w40 like crazy....but 10W-40 HDEO is constantly @ full mark ;)
I've also experienced that.
 
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12,668
Location
Middlesex County CT
This is a great point and can't be stated enough. There was an Australian poster who used to shout this quite often. He convinced me anyways haha 😅

Except CAFE doesn't say to use a thinner oil; it is a standard which the automakers must meet; many automakers have chosen thinner oils as one of the ways to meet the standard.

You can say "consensus"; Odd that the mfg that specify those thin oils have no problem making cars that routinely reach 300K miles.

Thick might protect better, but to a level unnecessary for passenger cars. A 12 lb maul drives nails more easily than a hammer, but I don't see carpenters carrying them around. j/k
 
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13,359
Location
Kendall, FL
Except CAFE doesn't say to use a thinner oil; it is a standard which the automakers must meet; many automakers have chosen thinner oils as one of the ways to meet the standard.

You can say "consensus"; Odd that the mfg that specify those thin oils have no problem making cars that routinely reach 300K miles.

Thick might protect better, but to a level unnecessary for passenger cars. A 12 lb maul drives nails more easily than a hammer, but I don't see carpenters carrying them around. j/k

Exactly.
Not sure why CAFE was brought up in this thread. Neither grade is resource conserving.
 
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