Mixing engine oil (different grades) advice?
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This is a discussion on Mixing engine oil (different grades) advice? within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; Is it ok to mix different grades of engine oil (0w-40 to 10w-40) when topping up if oil levels are ...

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    Mixing engine oil (different grades) advice?

    Is it ok to mix different grades of engine oil (0w-40 to 10w-40) when topping up if oil levels are dropping? The dealerships used Mobile 1 fully syn 0w-40 now they have all changed to Mobile super s 10w-40 apparently due to the poor fuel quality we get here in RSA. What about staying with the same grade but different brades eg Mobile mixed with Castrol? Hope you experts can shade some light for me thanks.

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    He simply abides. SD_GR's Avatar
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    Mobile is in Alabama.

    Mobil and Castrol both state that their lines contain products that are miscible.

    API oils are all miscible. ACEA oils are all miscible at the very least within "letter" classes (in practice, everything with anything at least IMO).

    The short answer is "yes."
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    Quote Originally Posted by SD_GR View Post
    Mobile is in Alabama.
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    Quote Originally Posted by SD_GR View Post
    Mobile is in Alabama.

    Mobil and Castrol both state that their lines contain products that are miscible.

    API oils are all miscible. ACEA oils are all miscible at the very least within "letter" classes (in practice, everything with anything at least IMO).

    The short answer is "yes."

    Spelling and typing obviously not my strong point.

    Ok so it is fine to mix the 2 brands of oil, what about topping up with 0w-40 into 10w-40 (mobil). I am half way between a service interval (12500km) and checked the oil level after car stands over night and level is at low, is this normal or is the oil consumption too high? Thanks.

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    I read your comment in the original post regarding having to change to 10W-40 due to a fuel problem and do not understand the reasoning. In any case, the difference between a 0W-40 and a 10W-40 is that the 0W will flow better when the car is cold. Since it is now summer, I can't imagine you'd care, so that's not a concern. If you are in Sutherland in winter, use a 0W or a 5W... you get the idea.

    The oils are miscible. You can add one to the other in any proportion and they will form a solution.

    Check your owner's manual and see if Subaru RSA specify a 10W-40. If you are under warranty and they don't specify a viscosity or type of oil, don't use it. Follow their requirements to the letter if under warranty. In practice it will make no difference for you while it's still summer. When winter comes around, if the temperatures drop low enough to warrant the use of a 0W vs. a 10W, adjust accordingly.

    You seem to be using 1L for 5,000+ km. This is actually fine IMO. In your manual or at the dealer they will tell you what they consider the "worry point" for oil consumption. Here, it is 1L per 1,600 km, and I've not had a car do that (yet?). Keep in mind two things: Use is not linear (it does not occur at a steady rate usually) and use is not constant but varies with use pattern, season, and oil type. So in any case check often and keep it topped up.
    Last edited by SD_GR; 01-06-2011 at 09:54 PM.
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    Mixing oil types/brands/viscosities isn't really a big deal. As long as you have enough oil in the system, it'll all mix together.
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    Quote Originally Posted by SD_GR View Post
    I read your comment in the original post regarding having to change to 10W-40 due to a fuel problem and do not understand the reasoning. In any case, the difference between a 0W-40 and a 10W-40 is that the 0W will flow better when the car is cold. Since it is now summer, I can't imagine you'd care, so that's not a concern. If you are in Sutherland in winter, use a 0W or a 5W... you get the idea.

    The oils are miscible. You can add one to the other in any proportion and they will form a solution.

    Check your owner's manual and see if Subaru RSA specify a 10W-40. If you are under warranty and they don't specify a viscosity or type of oil, don't use it. Follow their requirements to the letter if under warranty. In practice it will make no difference for you while it's still summer. When winter comes around, if the temperatures drop low enough to warrant the use of a 0W vs. a 10W, adjust accordingly.

    You seem to be using 1L for 5,000+ km. This is actually fine IMO. In your manual or at the dealer they will tell you what they consider the "worry point" for oil consumption. Here, it is 1L per 1,600 km, and I've not had a car do that (yet?). Keep in mind two things: Use is not linear (it does not occur at a steady rate usually) and use is not constant but varies with use pattern, season, and oil type. So in any case check often and keep it topped up.
    Yeah I asked the technical guys at head office here in South Africa why they decided to change the oil they put in the cars he told me that due to the poor quality of fuel we get here (95 Oct) using 0w-40 somehow stains the pistons or something, Iím not sure if itís just some story he made up or maybe they had cars that experienced problems using this grade of oil.
    Checked the ownerís manual recommends 5w-30, seems like 10w-30 and 10w40 is also acceptable. Thanks for the info guys.

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