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Oil Viscosity and Gas Mileage

Discussion in '80-Series Tech' started by alaskacruiser, Nov 13, 2003.

  1. alaskacruiser

    alaskacruiser

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    I've got a Q4U (as they* say)...
    Is it generally true that higher viscosity oils will give you lower gas mileage? The reason I ask is that I'm currently running Mobil 1 Ow-40 and I notice my gas mileage has gone down vs. the old dino 10w-30 I was using.

    Also, does using a higher viscosity oil provide any additional protection against wear? (assuming you are using it in the appropriate climactic conditions).


    *they = people who spend way too much time on computers
     
  2. Wayne

    Wayne Bought by His blood, kept by His power

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    I'm not a mechanical engineer, but lower viscosity oil should improve gas mileage because parasitic drag on the engine's reciprocating parts (primarily the crank shaft and connecting rods) and oil pump is reduced, which in turn requires less energy to make power, which = improved gas mileage. How much improvement...... who knows????

    Wayne S :D
     
  3. cary

    cary

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    This is one of those questions that can only be answered by "it all depends." Generally, a thinner oil will give slightly better fuel economy. This is one of the reasons that you see the trend toward lighter oils in new cars in the US, first xw-30 oils now xw-20 oils. I believe that the general rule is for every grade lighter you go, you will gain 1.5% in efficiency. Note that Mobil 1 0w-40 is one of the very few 40 weight oils that is certified as energy conserving by the API.

    That said, the rules don't always hold true. Look at post by Jim Chow and the responses to his post on Bobistheoilguy.com. It appears that on some older vehicles you may get an increase in miliage from better sealing with a slightly heavier oil.

    As far as protection of heavier weights, it depends on the individual vehicle. New hondas turn in incredably low wear numbers with 20 weight oils, BMW's seem to like 10w-60. Most cars seem happiest with a high 30 weight to low 40 weight. Also, driving conditions will effect the needed weight. If you are running at the track you will generally want to go up a grade because the higher oil temps the car will see will thin the oil out. I will see what my numbers look like with M1 0w-40 in a few weeks.

    Cary
     
  4. 91fj80

    91fj80

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    BMW's like 10w-60??
    my mechanic told me 15-50 was too thick for my 96 328i, he said it would mess up the hyd lifters.
     
  5. cary

    cary

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    It seems to depend on the model. The new M3 or M5 requires it. A couple of guys on bobistheoilguy.com have been using it and getting great numbers. You are correct that many models in cold weather have had trouble with thick oil and the vanos system. I have found that my Wifes 525 is quiter and stopped burning oil when I went from Mobil 1 15w-50 to M1 0w-40. I would stay with an xw-40 in the 528i, but if warm climates there is no problem with 15w-50.

    Cary
     
  6. cary

    cary

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    Fresh from Bitog, on BMW's:

    The update on the 0-40 from another dealer I visited today is that it is being made available due to a TSB (Factory Bulletin) to resolve ticking, clatter and/or valvetrain compaints from customers. I'm assuming in cars that use the BMW 5-30 synth (all models) as the M models specifically require the 10-60. He assured me it wasn't a direct replacement for the 5-30, nor was it specifically for the new 5 series. Guess it's just another band-aid to get people through the end of the warranty period...

    Very intersting....
     
  7. firetruck41

    firetruck41

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    OT along with the rest of you, no cruiser specific content. I've put ~50k miles (95k on it now) on our 525iT w/M50 non-vanos engine with 15w50 Mobil One, I've had plenty of problems with the car and spent lots of money to get it in good shape, but never had an engine problem or oil consumption (yet).

    It's for sale, for you BMW enthusiasts who can't live with out the best looking 5 series ever made, the E34 Touring wagon (way better looking than the sedan :flipoff2:) $7950 obo
     
  8. Pitbull

    Pitbull

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    Just wondering why you guys don't use Mobil 1 5w30 in you LC's? The owners manual calls for 5w30 so I just run the Mobil 1 5w30 since it is synthetic and I figured it would provide good wear protection. Change it every 5000 miles, been using it for around 100K miles out of the 130K on my 95 LC. Now I only get around 15 mpg. :(
     
  9. landandsea

    landandsea

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    [quote author=firetruck41 link=board=2;threadid=7509;start=msg63271#msg63271 date=1068856726]
    .... 525iT... the best looking 5 series ever made
    [/quote]

    You just hurt my 540iT's feelings...

    Ed