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10W30 or 15W40?

Discussion in 'Early CJ5 and CJ6 Tech' started by 69Willys, Feb 29, 2012.

  1. Feb 29, 2012
    69Willys

    69Willys Las Vegas, NV

    Las Vegas, NV
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    The "How do you start your engine" thread prompted me to post this. I've been doing a lot of reading about motor oil in old threads here and all over the net until my head is spinning. When I got my Jeep I removed the oil pan and found a layer of sludge on the bottom. I cleaned it out and then ran some Seafoam in the new oil. I used Castrol 10W30 because I was told it had lots of detergent. I changed the oil several times since then, always with 10W30. The Jeep always started great-- choke out, 2 squirts and fired up. The oil pressure was around 20+ at idle and 30+ at speed. I could hear some clacking when winding out 2nd and shifting to 3rd. Then, because of what I've read about zinc, flat tappet engines, etc, etc, etc, I decided to try some Rotella T 15W40. Now the Jeep is a little harder to start as if it's trying to overcome the resistance of the thicker oil--doesn't always start on the first try and have to crank it a little. Even after it's warmed up, it seems to be battling the thick oil, idling roughly enough to make me increase the idle speed on the carb. The oil pressure is now up to 30 at idle and 40+ at speed. The clacking is greatly reduced or gone and the leaks are fewer. Did I do the right thing in switching to the 15W40? If it matters, the weather here has been in the upper 60's low 70's. It will stay over 100 all summer. Which weight oil would you recommend?
     
  2. Mar 1, 2012
    curtcanada

    curtcanada L, L, and the POH!

    Western Slope, CO
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    I changed from 10-30 to 10-40 last summer, and experienced the exact same thing. Tried tuning it, and still couldn't get it to run as smooth. Went back to 10-30, since the engine wasn't getting worked hard, and the temp gauge was staying cool. Ran much better.
     
  3. Mar 1, 2012
    66cj5

    66cj5 Jeep with no name

    NorthWest Indiana
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    run straight 30w in mine (per factory manual). ran 10w30 for a while, but had too low of oil pressure when it warmed up at idle (could hear the valve train slapping)
     
  4. Mar 1, 2012
    colojeepguy

    colojeepguy Colorado Springs 2019 Sponsor

    At the foot of...
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    Have always ran 10W40 in mine-never any problems, even though my :v6: is all original and has 160K miles on it.
     
  5. Mar 1, 2012
    homersdog

    homersdog Tulsa, Ok 2020 Sponsor 2019 Sponsor

    Tulsa, OK
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    In my Dauntless I have always run 10w40 havoline or castrol, never considered another grade. Some of the lifters are slow to pump up some times but they get there after a few minutes.
     
  6. Mar 1, 2012
    mwinks-jeep

    mwinks-jeep I still love snow, Godspeed, Barney!

    Beautiful Bucks...
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    Any thoughts on 20/50????
     
  7. Mar 1, 2012
    '74Renegade

    '74Renegade Active Member 2019 Sponsor

    Fair Oaks, CA
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    I've been using 20/50 for 15+ years in my 304 with no ill effects. Keeps the oil burn down to a manageable level.
     
  8. Mar 1, 2012
    69Willys

    69Willys Las Vegas, NV

    Las Vegas, NV
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    Judging by how my Dauntless ran with the 15W40, I doubt it would even turn over with 20W50 in it :shock:. I just replaced with 5W30 Valvoline to try to quiet the valves more quickly on startup. Took it for a ride--running good again--good oil pressure--idling smooth again.
     
  9. Mar 1, 2012
    Mike C

    Mike C Member

    Austin, TX
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    I run 15 40 Rotella T in most of my carbureted vehicles. I even switched from Valvoline 20 50 in the Camaro because the full throttle pressure was too high. 10 40 was too low at idle. the 15 40 was the Goldilocks mix. The MB gets straight 30w and the A1 gets straight 40w. My F head oil pressure is still low with the 40, but at least acceptable.

    I have a 2N Ford Tractor that I run straight 30w in. It fires up at 30 psi cold, but after 20 minutes of operation it barely wiggles the needle off the pin. And I've been mowing with it like that for 9 years! My hope is the A1 will soldier on with the 40w.
     
  10. Mar 2, 2012
    1960willyscj5

    1960willyscj5 Well-Known Member

    Mesa, Arizona
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    20w-50 in the Willys F-134.
    Doesn't get that cold here, rarely below freezing. And above 100ยบ F from the beginning of April (usually) until the middle of October.
     
  11. Mar 7, 2012
    mwinks-jeep

    mwinks-jeep I still love snow, Godspeed, Barney!

    Beautiful Bucks...
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    Hmm OK so this goes back to my need to be taught about oil. Since i plan to drive this baby in snow a lot, do not use 20/50?
     
    Last edited: Mar 7, 2012
  12. Mar 7, 2012
    Warloch

    Warloch Did you say Flattie??? Staff Member

    Falcon, CO
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    That is correct - I only use 20/50 when I am in high heat and high load situations on any motor.
     
  13. Mar 7, 2012
    1960willyscj5

    1960willyscj5 Well-Known Member

    Mesa, Arizona
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    The books all say use 30 weight all year round.
     
  14. Mar 7, 2012
    69Willys

    69Willys Las Vegas, NV

    Las Vegas, NV
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    The 5W30 I'm running right now is perfect for me. Even on cold startups I have almost no valvetrain noise whereas I used to have 7-10 seconds of loud ticking with the heavier oils. I may go to 10W30 in the heat of summer but, for me, the 5W30 seems like a good, modern alternative to the recommended straight 30 weight.
     
  15. Mar 7, 2012
    1960willyscj5

    1960willyscj5 Well-Known Member

    Mesa, Arizona
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    Are you using Fossil Oil or Synthetic?
    They do act different.
     
  16. Mar 7, 2012
    69Willys

    69Willys Las Vegas, NV

    Las Vegas, NV
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    Fossil...Valvoline Max Life High Mileage in the red jug
     
    Last edited: Mar 7, 2012
  17. Mar 8, 2012
    duffer

    duffer Rodent Power 2019 Sponsor

    Bozeman, MT
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    Same here in the 3B. 20-50 for summer, 15-40 winter. Just about everyone you talk to will have a different opinion.

    For my off road adventures, I am usually running around 500 rpm and 180 to 190 degrees. I want full oil pressure at that rpm/temp so I am wasting gas mileage pumping against the pressure relief spring (set at 60 psi) in the big block pump but it works and has worked for several decades.

    My 60's vintage Case diesels all run straight 40, as per specs. If I use them when it's cold, I always plug them in-too painful to watch the oil pressure gage otherwise.
     

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