Why not use 0w16 in a 0w20 engine?

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4
Location
Alabama
Long time reader, first time poster - I drive a 2018 3.5L 2WD Tacoma, 25K miles, just out of toyota care. I rarely haul, and it's my daily driver over flat terrain. It's never seen a hard day's work, and couldn't crawl over a (already flattened) Coke can in the grocery store parking lot. I don't hypermile, but I do limit my speed, and drive like my grandpa on the way home from a fishing trip. Lifetime average MPG is 23.5, with recent fuel economy nearing 25 MPG after the change in driving habits. I live in the SE, hot AF in the summers, but fuel economy usually increases through July in this truck. I'm always looking for something to try, and that led me to a question that I would like a few opinions on. With the availability of 0w16, and the upcoming change to GF6, why shouldn't I use 0w16 to improve fuel economy? I'm ready to be burned at the stake, but hear me out. Pennzoil's 0w16 100C viscosity is stated at 7.4, which puts it firmly in the 20 grade category. The low temperature viscosity is near that of Mobil 1's cold temperature rating (low 4K's). The difference is of course in the HTHS, at 2.3 instead of 2.6. I've read in multiple posts here that 0w16 requires a variable displacement oil pump. I'm not sure I fully understand why that is necessary, when a fixed displacement pump will move the same volume of fluid, regardless of the viscosity. It seems as if the oil pump should move the same amount of 100C 16 grade, as 100C 20 grade at any given temperature, the difference being the energy required to do so. Can someone offer a quick explanation as to why this is so? My other reasoning is that I can use pretty much any oil that's commonly available and not suffer any realizable consequences. I can run XwY up to {10,40} and be fine, from what I've read on TW and other forums with UAO. Why is this case really different? There's also my wife's 5th gen CR-V, which can (her's doesn't) suffer from fuel dilution, and come out with perfectly fine UOA, starting from 0w20, and that's with a GDI/turbo! Alternatively, what's the lowest 100C viscosity 0w20 on the market? I've sorted through PQIA's database a few times, but they all seem to generally be in the 8.4 range. Thanks, Kyle
 

Astro14

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If you're hoping to get better MPG out of a Toyota truck by changing oil, you're going to be disappointed. The Tacoma is a great truck, but it has not ever been fuel efficient, and that tiny change in oil viscosity won't make a measurable difference. But in hot AL summers, too low a viscosity carries some risk. Stick with the factory recommendation.
 
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KBentley57

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Alabama
Thanks Astro, I'm not hoping for an improvement, per se - though I'd take one if it came 'for free'. It's more a what-if question to help me understand the new standards. The blurb on fuel economy was for those who are familiar with this truck, and know that achieving that kind of FE means very low average engine load. I know that there's no way to tell, beyond running it and collecting data. However, if there's something I overlooked, I'd want it shoved back in my face, IE "0w16 is only made of silly putty, for use in playschool engines you big dumy." Maybe my mind is starting to run rampant, I've been working from home for about two weeks, and am starting to get a little bit fidgety!
 
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2,343
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South Carolina
[email protected] is in the same range for W16 and W20 but that's not your enemy. HTHS is the enemy in older engines for 0W-16. It has been laboratory engine tested that an HTHS of 2.6 is the absolute minimum for engines not designed to run on W16 oils. This is where the fuel economy gains are with W16 but makes them prohibitive for engines not designed to use them.
 
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Connecticut
I'm curious what grade is specified for this engine in the rest of the world. I suspect it's heavier than 0W-16. Personally I'd go with a heavier grade in the Southwest.
 
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KBentley57

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Alabama
I see. I was trying to reason out why the KV values of the 16 grade (and other grades witheachother) co-reside with the 20 grade, I suppose HTHS and KV values are not necessarily correlated between/within grades? On a side note, if you have a good source of literature for that HTHS 2.6 lab test, I'd be curious to read it. Thanks!
 

KBentley57

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Alabama
@Sam 0w20 in the US, I've read 5w30 elsewhere, but I can't confirm that. @simple_gifts I've pretty much maximized the extent to which I control my speed/acceleration. I check my tires pretty regularly, I'm thankful that the dash has a TPM display so I can keep an eye on it. Just tossing around some ideas.
 
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There are way too many variables in this kind of experiment. I'm not a scientist but since you are then you should have realized this. Driving habits. Tire inflation Engine upkeep Outside temperature Gasoline pump variables Weather besides temperature. ( wind for example) Driving route. ( hilly versus flat. Altitude And a whole bunch more. To cut to the chase, you won't notice any difference. Run the oil grade that is recommended by the auto manufacturer.
 
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35,636
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NY
Originally Posted by Yah-Tah-Hey
Toss it in. It's your vehicle and your choice.
+1 It's hard to say if it's a good idea or not. You'll get some educated guesses, uneducated guesses, but little to no long term real world data. Having said that you'll find out eventually if it was a wise choice or not, my guess is it will take years to find out.
 
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In recent years Subaru has switched from using 5w30 as their standard factory oil viscosity to 0w20 on most of their vehicles not primarily because of minimal fuel economy savings but rather because of environmentalist regulations regarding carbon emissions. The additional fuel savings that may come from using a lighter oil are really just a thrown in, CAFE standards are what it is all about be it Subaru, Toyota, or any other brand automaker.
 
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South Carolina
Originally Posted by KBentley57
I see. I was trying to reason out why the KV values of the 16 grade (and other grades witheachother) co-reside with the 20 grade, I suppose HTHS and KV values are not necessarily correlated between/within grades? On a side note, if you have a good source of literature for that HTHS 2.6 lab test, I'd be curious to read it. Thanks!
I looked and cannot seem to find the paper. It was old but relevant to today's (prior 0w-16) engines. Problem is I have hundreds of saved papers to go through!
 
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