Fuel mileage 5w-40 vs 10w-30 in newer dsl pickups

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I have a 2014 F250 PSD, and have put 80K on her so far. Have run T6 (5w-40) for many OCIs, 15w-40 for some OCIs, and 10w-30 for only one OCI. The 10w-30 OCI was a few years ago, and it got the best mpg. I'm not too particular about mpg, so I can't recall by how much but I'd guess 0.5 mpg or so. Is it possible something else caused it - sure. Many things affect my mpg, such as cetane, temperature, fuel, oil, etc., but my belief is that the 10w-30 gets the best mpg. However, I don't use 10w-30 in general because it's not recommended for towing and bio fuel which apply to me.
 
Originally Posted By: another Todd
So then I am basically hearing no real difference in 5w-40 vs 10w-30 in diesel pickups. So why would anybody use a 10w-30? I think it is proven the 5w-40 provides better protection if you load it down or get it real hot.
I think in OTR trucks it can make a difference just due to the very long runs they make with the fairly constant speeds they are driven. In LD diesels which see a wide variation in operating conditions, it may or may not make a difference. I am running 10W-30 now just to see how it works, but I prefer 5W-40 synthetic or 15W-40 synblend.
 
A 10w-30 conventional or blend might also be cheaper than a synthetic, and that holds particularly true if OCIs aren't being extended as would ordinarily be possible with a 5w-40 synthetic. So, there are valid reasons to choose a 10w-30 HDEO.
 
Originally Posted By: another Todd
So then I am basically hearing no real difference in 5w-40 vs 10w-30 in diesel pickups. So why would anybody use a 10w-30? I think it is proven the 5w-40 provides better protection if you load it down or get it real hot.


Per UOA I have always had stellar performance with 10w-30 currently in my 6.7 and previously
in my 6.0.
Many years ago I tried three runs of 5w-40 in my 6.0, by far the worse UOA's I had ever had, wear metals shot up, and viscosity was lower than any 10w-30 run.
 
Originally Posted By: another Todd
So then I am basically hearing no real difference in 5w-40 vs 10w-30 in diesel pickups. So why would anybody use a 10w-30? I think it is proven the 5w-40 provides better protection if you load it down or get it real hot.


So then why are ALL the OEM heavy diesel mfg's, factory filling their engines with 10w30?
 
Originally Posted By: BoiseRob
Originally Posted By: another Todd
So then I am basically hearing no real difference in 5w-40 vs 10w-30 in diesel pickups. So why would anybody use a 10w-30? I think it is proven the 5w-40 provides better protection if you load it down or get it real hot.


So then why are ALL the OEM heavy diesel mfg's, factory filling their engines with 10w30?
In long distance, fully warmed up, steady state speeds-there is a measurable difference. That's what's driving the low HTHS FA-4 oils, the engine builders have to build an engine that can handle them.
 
Isn't the switch to 10w 30 to help achieve fuel mileage efficiency set by government MPG goals? Thus, all mgfs of diesel engines moving to that as a factory fill? Whether that is good or bad for engine longevity...not completely sure either way. UOAS over time will tell...but I have seen some on here that don't look all that bad. Once my stash of 5w40 is gone I might try running it. Just not sure why ford recommends 10w 30 for normal usage and 5w40 & 15w40 for bio diesel and 5w40 for severe usuage...which I lean towards. My application is keeping me in the 5w40/15w40 area...right or wrong...don't know.
 
Originally Posted By: bullwinkle
Originally Posted By: BoiseRob
Originally Posted By: another Todd
So then I am basically hearing no real difference in 5w-40 vs 10w-30 in diesel pickups. So why would anybody use a 10w-30? I think it is proven the 5w-40 provides better protection if you load it down or get it real hot.
So then why are ALL the OEM heavy diesel mfg's, factory filling their engines with 10w30?
In long distance, fully warmed up, steady state speeds-there is a measurable difference.
I agree and as I said before for the average LD diesel owner, I doubt there would be any MPG difference that can be attributed directly to the oil versus other variances.
 
Originally Posted By: mbacfp
Isn't the switch to 10w 30 to help achieve fuel mileage efficiency set by government MPG goals?

Sure, that's important. But, just like in passenger cars, the average user is never going to tell the difference in fuel economy between one grade and another. It makes a difference in the grand scheme of things, but certainly isn't going to be significant in an average fillup for a normal motorist.
 
Yes, individualy MPG savings will be insignificant (unless you drive a lot)...however in the aggregate (from a public policy perspective) that should add up to less oil used in the overall economy.
 
Yep, for sure. Personally, I cannot calculate a difference between SN/GF-5 5w-30 and CJ-4/SM 5w-40 in my G37. Of course, that doesn't mean it's not there. My dad would be shaking his head right now at me. He was never a fan of thicker oils, particularly where they really weren't necessary.
wink.gif
 
While the mpg game might play into some of the reasoning why OEM's are factory filling with 10w30 in diesels now, it could be more than that. I have extensive UOA's on both 15w40, 5w40, and 10w30 on my commercial truck. Of all of them, the 10w30 actually seems a little more sheer stable over the oil change interval. Not that the others are failing in any way, but the 10w30 holds original viscosity more closely. The 5w40 was the worse for sheering almost out of grade, at least in my engine. I see no appreciable change in wear numbers or anything else by using a 10w30. But I did get a up tick on mpg over 4 mo periods from one year to the other using 10w30. And those are not lie-O-meter mpg numbers, but actual pump to pump calculated averages.
 
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