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Thread: 15w-40 vs 5w-40

  1. Top Of Page | #11
    Basic Member hray's Avatar

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    Re: 15w-40 vs 5w-40

    You'll be fine with either. Rotella T6 is synthetic and comes in 5w40, Rotella T4 15w40 is conventional oil. I'm pretty sure you won't find a full synthetic in 15w40. Factory fill from Cummins is Valvoline premium Blue 5w40 full synthetic because they don't know what climate they will be operating in. It's fine to switch between the 2 weights. I use VPB 15w40 or Rotella T4 15w40 depending whom has it on sale at time of oil change. Currently using VPB, I also keep 3 gallons of oil and a extra filter between oil changes so I don't have to hunt for sales. When I use the spare oil I go on the look out for sales to restock. Hray


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  3. Top Of Page | #12
    HKBIGDADDYDIESELDAN's Avatar

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    Re: 15w-40 vs 5w-40

    Quote Originally Posted by hray View Post
    You'll be fine with either. Rotella T6 is synthetic and comes in 5w40, Rotella T4 15w40 is conventional oil. I'm pretty sure you won't find a full synthetic in 15w40. Factory fill from Cummins is Valvoline premium Blue 5w40 full synthetic because they don't know what climate they will be operating in. It's fine to switch between the 2 weights. I use VPB 15w40 or Rotella T4 15w40 depending whom has it on sale at time of oil change. Currently using VPB, I also keep 3 gallons of oil and a extra filter between oil changes so I don't have to hunt for sales. When I use the spare oil I go on the look out for sales to restock. Hray
    X2 I always try to get oil on sale and stock up also been using Valvoline Premium Blue on 4 Cummins motors great oil never one lick of a problem with nearly 1 million miles of use

    2012 Cummins Ram 6.7L MM3 tuner full 5" Flo Pro TBE Exhaust LWBCC 4x4 Mag Hytec Double Deep Transmission Pan , Mag Hytec Rear Diff Cover
    Airlift part # 57595 7500lbs airbags ,Nitto Ridge Grapplers 35/12.50/20 on XD 829 Big Hoss ll Satin Black Machined Dark Tint 20 x 9 with + 18 offset rims,MM3 Tuner With full Custom Tunes by Ray at DRD , Autometer A13117 Pillar Pod , Edge 98004 mount adapter , Mag Hytec front diff cover, SuperNova V4 LED Headlight Bulbs

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  5. Top Of Page | #13
    mr.travo's Avatar

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    Re: 15w-40 vs 5w-40

    Good info in here.

    I was looking online the other day and came across Rotella 15w-40 full synthetic.

    https://rotella.shell.com/en_us/prod...motor-oil.html

    Any thoughts on using this?

    I am in TX where the summers get pretty hot ~100 degrees.

    Thanks!

    Since the DRD delete, this truck is 100 times better! Outstanding fuel mileage and plenty of power. Thank you Ray!!!

    2006 Ram 2500 4x4 5.9 --Traded--
    2007 Ram 3500 4x4 5.9 G56 --Sold--

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  7. Top Of Page | #14
    Aj Grubb's Avatar

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    Re: 15w-40 vs 5w-40

    5W-40 T6 is just fine for any and every climate you will experience in the USA.

    It will not be too thin in hot weather.

    Run it with confidence.


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  9. Top Of Page | #15
    mr.travo's Avatar

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    Re: 15w-40 vs 5w-40

    Thank you AJ!

    Since the DRD delete, this truck is 100 times better! Outstanding fuel mileage and plenty of power. Thank you Ray!!!

    2006 Ram 2500 4x4 5.9 --Traded--
    2007 Ram 3500 4x4 5.9 G56 --Sold--

  10. Top Of Page | #16
    Rambling Rump Ranger! SyN's Avatar

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    Re: 15w-40 vs 5w-40

    Remember: The W rating is for Winter 5W / 15W - Once either oil has reached full operating temp = Both oils are @ the 40W viscosity (No real world difference)

    The 5W-40 viscosity does contain way more viscosity improvers... Not a big deal but some oil gurus say less is better for lower wear #s - hence why 10W-30 HDEO is becoming so popular.
    Thousands of OTR drivers are switching to the 10W-30 viscosity due to higher fuel savings with No Sacrifice in engine wear.

    SyN Disclaimer: I am by no means blabbing any bad info about the 5W-40 viscosity! (Billions of miles have been accumulated on 5W-40 & 15W-40) Each viscosity has its own ideal situation.

    Edit: Due to popular believe Castrol proved years ago that most engine wear occurs within the warm up to operating temp process - Not @ Start Up - This is why (cold) start up idling is frowned upon. Plus in some cases this is where a good amount of fuel dilution takes place...

    2017 Bighorn (Delmonico Red & Chrome) CC-HD2500-4WD-6.7L-3:42w/Anti-Spin
    Oil: -SHELL- Rotella T6 5W-40 & T5 15W-40 combo w/LF16035
    68RFE/BW44-46/Power Steering: -Red Line- C+ ATF
    Frontend & Rearend: -Red Line- SAE GL-5 75W-90NS
    Many Small Mods: Interior & Exterior
    Mileage: 28,541

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