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Thread: 5W40 Vs. 15W40 Oil?

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    sdjimbo's Avatar

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    5W40 Vs. 15W40 Oil?

    Hey everyone, I am sure this question has popped up before; my apologies.

    I have a 12 3500 SRW with 165k miles.

    I am currently running 15W40 and am about to change my oil.

    With February, I am considering trying 5W40 for a few months.

    I live in northern Virginia, so it doesn’t get below 10F very often.

    I just wanted to get some advice from all of you.

    I have seen on other platforms that you get better MPG and cooler temperatures and stuff.

    I thought I would ask the Cummins professional here because I trust the information you all provide to our community more than anywhere else.


    Sent from my iPhone using Tapatalk


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  3. Top Of Page | #2
    CrazyTrain's Avatar

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    Re: 5W40 Vs. 15W40 Oil?

    Quote Originally Posted by sdjimbo View Post
    Hey everyone, I am sure this question has popped up before; my apologies.

    I have a 12 3500 SRW with 165k miles.

    I am currently running 15W40 and am about to change my oil.

    With February, I am considering trying 5W40 for a few months.

    I live in northern Virginia, so it doesn’t get below 10F very often.

    I just wanted to get some advice from all of you.

    I have seen on other platforms that you get better MPG and cooler temperatures and stuff.

    I thought I would ask the Cummins professional here because I trust the information you all provide to our community more than anywhere else.


    Sent from my iPhone using Tapatalk
    Stick with the 15W-40.

    2021 Ram 3500 DRW, H.O., bypass oil filtration, bypass coolant filtration, S&B CAI, 4:10’s
    2wd low loc kit.
    Reacquired 2001 3500, 5.9 nv4500, dually cab and chassis, 5” straight pipe, edge juice w/attitude. Otherwise all stock…..for now.

  4. Top Of Page | #3
    MOD watersupply189's Avatar

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    Re: 5W40 Vs. 15W40 Oil?

    Quote Originally Posted by sdjimbo View Post
    Hey everyone, I am sure this question has popped up before; my apologies.

    I have a 12 3500 SRW with 165k miles.

    I am currently running 15W40 and am about to change my oil.

    With February, I am considering trying 5W40 for a few months.

    I live in northern Virginia, so it doesn’t get below 10F very often.

    I just wanted to get some advice from all of you.

    I have seen on other platforms that you get better MPG and cooler temperatures and stuff.

    I thought I would ask the Cummins professional here because I trust the information you all provide to our community more than anywhere else.


    Sent from my iPhone using Tapatalk
    Stay with the 15W40.

    I wouldn't mess with it if that’s what’s been in it the whole time.

    If you lived in sub-zero temperatures, thinner oil would be better.

    As for improving mileage and stuff. I doubt very seriously that it would improve fuel mileage.

    I’ve been running 15W40 since the truck was new.

    I never had any issues, and I now have 120k on it.


    2016 Ram Laramie 3500, G56, 6.7, CC, 4x4

    2016 RAM 3500 4x4 Laramie Crew Cab ,G56

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  6. Top Of Page | #4

    Re: 5W40 Vs. 15W40 Oil?

    Quote Originally Posted by sdjimbo View Post
    Hey everyone, I am sure this question has popped up before; my apologies.

    I have a 12 3500 SRW with 165k miles.

    I am currently running 15W40 and am about to change my oil.

    With February, I am considering trying 5W40 for a few months.

    I live in northern Virginia, so it doesn't get below 10F very often.

    I just wanted to get some advice from all of you.

    I have seen on other platforms that you get better MPG and cooler temperatures and stuff.

    I thought I would ask the Cummins professional here because I trust the information you all provide to our community more than anywhere else.


    Sent from my iPhone using Tapatalk
    OK, I will say the opposite, so don't hate everyone.

    I run the 5W40, specifically Amsoil, in my two-gen RAMS only because it's Amsoil.

    Their cold flow test and general tests are impressive, but for some reason, 5W40 is the only weight oil they list for my 2016 and 2018.

    Like you, I remember wondering if it was OK to run that oil year-round.

    I called them, and they said yes, it is absolutely.

    I also run it with their bypass system 60k mile filter.

    I am not trying to sell you anything.

    I prefer their oils based on the results of independent tests I have seen over the years and on my vehicles.

    Plenty of other great oils are out there, and if you want to stick with 15W40, stick with it.

    I can't say I have seen mileage increase or anything, but my Blackstone lab tests looked awesome before testing this oil.

    I will say that if you have a 5th Gen, I won't screw around with any other weight of oil than what they call for.


  7. Top Of Page | #5
    sdjimbo's Avatar

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    Re: 5W40 Vs. 15W40 Oil?

    Quote Originally Posted by rsl0311usmc View Post
    OK, I will say the opposite, so don't hate everyone.

    I run the 5W40, specifically Amsoil, in my two-gen RAMS only because it's Amsoil.

    Their cold flow test and general tests are impressive, but for some reason, 5W40 is the only weight oil they list for my 2016 and 2018.

    Like you, I remember wondering if it was OK to run that oil year-round.

    I called them, and they said yes, it is absolutely.

    I also run it with their bypass system 60k mile filter.

    I am not trying to sell you anything.

    I prefer their oils based on the results of independent tests I have seen over the years and on my vehicles.

    Plenty of other great oils are out there, and if you want to stick with 15W40, stick with it.

    I can't say I have seen mileage increase or anything, but my Blackstone lab tests looked awesome before testing this oil.

    I will say that if you have a 5th Gen, I won't screw around with any other weight of oil than what they call for.
    Thank you for the information.

    I will stick with the 15W40 but with the higher-end synthetic oils like AMSOIL or Hot Shot Secret oil.

    I know it's expensive, but I'm starting to believe you get what you pay for.


    Sent from my iPhone using Tapatalk


  8. Top Of Page | #6
    Watch Dog! Corkey's Avatar

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    Re: 5W40 Vs. 15W40 Oil?

    I run the 5W40 full synthetic with the Lucas oil stabilizer.

    You'll get twice the miles before needing to change the oil.

    I swear any Lucas products are worth their weight in gold.

    II 60HP STICKS, II 33% CP3, II S464 2ND GEN SWAP, FASS 165 TITANIUM SIGNATURE SERIES, AFE INTAKE HORN, S&B FILTER, 5" TURBO BACK, ALPHAREX HEAD LIGHTS, 38X13.5X20 RAZOR M/T, MOTO METAL RIMS, 6" LA LIFT KIT, COMPLET MM3 KIT, BUILT TRANSMISSION, 6 BOLT REDHEAD STEERING BOX

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  10. Top Of Page | #7
    I WILL STAND! AK Bob's Avatar

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    Re: 5W40 Vs. 15W40 Oil?

    I follow the recommended oil type and weight in my owner's manual.

    For me, it’s Rotella T6, 5W40 year round.

    The oil weight should be selected based on the anticipated operating temperature range.



    2014 RAM 3500 (Aisin) 3.73 4X4 Limited Crew Cab Long Bed DRW. Oil Bypass Filter, Fuel Filtration Kit, Cold Air Intake, City Diesel Actuator and 50 Gallon Aux Fuel Tank.

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  12. Top Of Page | #8
    MOD watersupply189's Avatar

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    Re: 5W40 Vs. 15W40 Oil?

    I run the Hot Shots black diamond 15W40, which has higher zinc content for better protection, and you can go two to three times longer between oil changes.

    Just change the oil filter at the manufacturer's recommendation.

    This black diamond is only for deleted vehicles.


    2016 Ram Laramie 3500, G56, 6.7, CC, 4x4

    2016 RAM 3500 4x4 Laramie Crew Cab ,G56

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  14. Top Of Page | #9

    Re: 5W40 Vs. 15W40 Oil?

    What's everyone's oil change interval mileage?

    I am curious.

    I won't lie. Even running the bypass and Amsoil, I hate letting it get near 25 percent oil life on the dash and probably do overkill oil changes.


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  16. Top Of Page | #10
    MOD watersupply189's Avatar

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    Re: 5W40 Vs. 15W40 Oil?

    Quote Originally Posted by rsl0311usmc View Post
    What's everyone's oil change interval mileage?

    I am curious.

    I won't lie. Even running the bypass and Amsoil, I hate letting it get near 25 percent oil life on the dash and probably do overkill oil changes.
    Even though I'm running the Hot Shots black diamond, and they state that the oil life can be extended a lot, I constantly change mine every 12 months and 10 - 15k miles.

    I'm paranoid about letting it go longer than that. LOL


    2016 Ram Laramie 3500, G56, 6.7, CC, 4x4

    2016 RAM 3500 4x4 Laramie Crew Cab ,G56

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