1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

[off topic] fuel economy and synthetic engine oils

Discussion in '80-Series Tech' started by Jim_Chow, Nov 12, 2003.

  1. Jim_Chow

    Jim_Chow

    Messages:
    2,479
    Likes Received:
    5
    Joined:
    Apr 28, 2003
    Location:
    Turquoise Trail, N NM
    For anyone interested, I have been running Shell Rotella T synthetic 5w40 for a while (WalMart, $13/gal) and recently switched to M1 10w30 (WalMart, $17/5 qts). Fuel economy consistently was 5% lower w/ the M1 10w30. Fuel was the same (chevron 91, mtbe additive), driving routes were the same (commuting, avg speed of 35-55mph, 22 mi each way, most flat, temps around 80-85/50-60F in So. AZ).
    Vehicle is a '86 4runner, 22re 4-cyl, 153K mi, new valve seals/cam/rockers/exhaust valves/HG/header+cat+catback 25K mi ago, original lower block. No cruiser content, other than how to possibly improve fuel economy based on the choice of motor oil. :) Also, oil burnoff in my '01 honda prelude SH (1 qt per 3K mi on dino 5w30) was eliminated after switching to M1 Delvac 5w40. That's obviously a thin oil issue. Damn CAFE! I saw that the recommended oil in Japanese motor mags is M1 5w40 or other brand 10w30's and 10w40's, not 5w30's (guess they think 5w30 is too thin?).

    Here are some responses....
    ---------------------------------------------------------
    I just started useing Rotella T 5w40 in my Wife's 2003 VW Golf 2.0 about 4 months ago. Initially, I used Mobil1 5w30 immediately after break-in. We decided to switch over to Rotella strictly based on lowering maintanence cost since I change it every 3-5k miles. (...also because 5w40 is the recommended weight per VWoA) We've noticed no change in MPGs with the switch, just a slightly fatter wallet.
    ---------------------------------------------------------
    It's not Rotella in particular, it's the thicker oil. I have seen the same thing when I switched from 10W-30 to 10W-40 in my SAAB and so have other people. Try any 10W-40 or 5W-40 oil and you should see same fuel economy numbers as with Rotella.

    The theory I have is that the thicker oil reduces internal friction more than energy wasted due to thicker oil. This seems to be the norm for engines with 70k-80k miles or more.
    ---------------------------------------------------------
    40 wt. might also create a better ring seal than thinner oils in higher mileage engines.
    ---------------------------------------------------------
    If that's an '86 4Runner, then I suspect that it has a few miles on it. If that's so, then you are probably getting some blow-by with the lightweight M1, whereas the heavier 5W40 is giving you better compression and therefore better fuel economy.
    ---------------------------------------------------------
     
  2. firetruck41

    firetruck41

    Messages:
    5,732
    Likes Received:
    24
    Joined:
    Mar 27, 2003
    Location:
    Camas, WA USA
    I just picked up Rotella T synthetic 5w-40 for my next oil change, it's significantly cheaper than the M1 10w-30 I've been using, and I hope it helps with consumption. Fingers crossed!
     
  3. Qball

    Qball

    Messages:
    3,413
    Likes Received:
    2,025
    Joined:
    Jul 26, 2012
    Location:
    SoCal
    I've changed between light and heavy oils and do not notice any fuel economy differences. My block has 220k on it and it doesn't drip much either.
     
  4. DARKNESS

    DARKNESS SILVER Star

    Messages:
    1,750
    Likes Received:
    631
    Joined:
    Jan 6, 2013
    Location:
    Golden, CO
    When did you switch? I notice a difference in mileage when gas stations switch from summer blend to winter blend.
     
    Qball likes this.
  5. BiggestAUfan

    BiggestAUfan

    Messages:
    63
    Likes Received:
    7
    Joined:
    May 30, 2009
    Location:
    Gulf Coast
    What's the difference between the 5 or 10 before the W and the 30 or 40 after?
     
  6. Hornd

    Hornd SILVER Star

    Messages:
    2,469
    Likes Received:
    1,339
    Joined:
    Dec 18, 2013
    Location:
    Toledo, OH
    Trying to pinpoint a 5% MPG difference with accuracy is highly improbable but not impossible.
     
    Last edited: Jun 8, 2016
    John McVicker likes this.
  7. scottryana

    scottryana

    Messages:
    8,781
    Albums:
    1
    Likes Received:
    4,716
    Joined:
    Feb 2, 2004
    Location:
    Richmond, VA
    Yeah I am with darkness. I would bet any difference seen was due to more ethanol in summer gas mix.
     
  8. OLD DAWG

    OLD DAWG

    Messages:
    126
    Likes Received:
    11
    Joined:
    Mar 6, 2010
    Location:
    Montrose, CO
    We definently notice the summer/winter blend thing as well. As far as oil, find one your vehicle and wallet likes and go with it. What I've noticed over way too many years is that certain vehicles like certain oils as well as fuels better. It's just like women prefer certain wines over others. Give them what they like and life becomes easier.
     
  9. n00g7

    n00g7

    Messages:
    460
    Media:
    4
    Likes Received:
    258
    Joined:
    Oct 3, 2014
    Location:
    Lone Star State
    Cold and Hot weight. If you live in cold climates you might go with a lower cold number... On my Jeep in VT I run 10W-40 summer and 5 or 0W in the winter (just depends on what's sitting around). Just do two oil changes a year, sometimes no filter as it doesn't get that many miles on it.