Can 5W-20 be mixed with 5W-30?

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Thread: Can 5W-20 be mixed with 5W-30?

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    Default Can 5W-20 be mixed with 5W-30?

    My friend left me about 1 quart of 5W-20 oil and I was wondering can I mix that with 5W-30 for my Tundra? Any oil experts out there think this is okay to do? It's Mobil 1 Synthetic and that's all I run now since I have over 100k on my truck. I don't want the 5W-20 to go to waste! Thanks again!
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    Default Re: Can 5W-20 be mixed with 5W-30?

    That one quart wont matter. It'll thin it out a tad, but we are talking about 5 quarts of 30 weight to one quart of 20 weight. I doubt the truck will notice.
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    Default Re: Can 5W-20 be mixed with 5W-30?

    NO...The Truck will blow up!!!!



    No. should be fine. 5W-20 is a relatively new weight that I think got started with the Honda V-Tec engine line. This time of year, especially if you are in a cold climate, won't matter.

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    Default Re: Can 5W-20 be mixed with 5W-30?

    I read somewhere you should never mix weights of oil. Use it in your lawnmower.

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    Default Re: Can 5W-20 be mixed with 5W-30?

    In such situations, I have been known to add a quart of similar, but not identical, oil to my Toyota Supras. My cars have never presented any problems as a result of my somewhat cavilier actions! I say "go ahead and pour it in."
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    Default Re: Can 5W-20 be mixed with 5W-30?

    Mixing viscosities doesn't matter- your final "weight" is the average of whatever you add. My wife's car runs 10w30 and takes 4.5qts. I just buy the 4qt jug of 10w30 and top it off with 10w40 or 20w50 (for my Land Cruiser) - whatever's nearby when I'm changing the oil. The Land Cruiser holds 8 qts so I've always got some sitting around. Been doing this for years with no issues.

    You can't mix between regular/synthetic blend/full synthetic but mixing weights, especially if they're by the same manufacturer, is no problem.
    Last edited by KCfj40; 01-10-2008 at 08:11 PM.
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    Default Re: Can 5W-20 be mixed with 5W-30?

    No mixing of synthetic blend?
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    Default Re: Can 5W-20 be mixed with 5W-30?

    Quote Originally Posted by Tundragod View Post
    No mixing of synthetic blend?
    Syn blen is by definition a mix. But, I'd say why not just change the oil w/ the same type.
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    Default Re: Can 5W-20 be mixed with 5W-30?

    Quote Originally Posted by Marty358 View Post
    I read somewhere you should never mix weights of oil. Use it in your lawnmower.
    Use ONLY straight 30w in your lawnmower...seriously.

    Mixing weights is not a big deal. The bottom line is, are you getting a weight that's appropriate for you application and climate.

    Mixing synthetic and dino is not a big deal...it's just that you are diluting the synthetic with dino, which is a problem if you are doing extended drain intervals.

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    Mech. Engr. / Mechanic single's Avatar
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    Default Re: Can 5W-20 be mixed with 5W-30?

    Quote Originally Posted by shall36 View Post
    Use ONLY straight 30w in your lawnmower...seriously.
    My lawn mower calls for 15w40. Go with the mfg. rec.
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    Default Re: Can 5W-20 be mixed with 5W-30?

    Wow...that's a new one. B&S, Techumseh, and the other run of the mill air-cooled lawn 4-stroke engines have used straight 30W for years. Remember, when that engine heats up, the oil drops to 15W. In warmer climates, not the best things for an air-cooled engine. Maybe some of the new engines with oil pumps can use the 15W oils?

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    Default Re: Can 5W-20 be mixed with 5W-30?

    Quote Originally Posted by shall36 View Post
    ...Remember, when that engine heats up, the oil drops to 15W. In warmer climates, not the best things for an air-cooled engine. Maybe some of the new engines with oil pumps can use the 15W oils?
    I think your a little confused how a multi weight oil works. When a 15W-40 heats up it's viscosity doesn't drop to 15 weight. It's viscosity does drop as heat is applied but it wouldn't drop anymore than a straight 40 weight oil would. The "15W" rating simply means that at a set temperature (0 degrees C ?) the 40 weight oil will act (have similar viscosity) as a straight 15 weight oil would. It's still thicker when cold (you can't change fluid dynamics entirely), just not as thick as a straight 40 weight oil would be at colder temperatures.

    My Honda lawn mower calls for 10W-30 and has had M1 in it since new. I'm thinking about putting 5W-30 in it next time as I've used up all my M1 10W-30. That way all the engines in my "fleet" will be on the same oil.
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    Default Re: Can 5W-20 be mixed with 5W-30?

    You're right....I'm bass ackwards...
    Last edited by shall36; 01-11-2008 at 08:40 PM.

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