Difference between 10W-30 and 5W-20?

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Okay to use 10W-30 motor oil if owner manuel says to use 5W-20?
Update : It's a 2005 Mazda 3 w/120k miles.
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It sounds as if you have a late model Ford or Toyota. The lower the first number, the faster the oil pump forces a greater volume of oil to frictional surfaces at start-up. *It's good medicine because 80% of all engine wear occurs during cold and hot starts. You'll also get better fuel economy because the oil pump turns easier.

You do as you like with the selection of oil viscosity. Keep in mind while the car is under warranty and you have an engine problem, the oil is the first place a dealer looks. I wouldn't be caught dead with an out of factory recommended oil in the crankcase.

Form your own conclusion by reading what the advantages and disadvantages of *viscosity index improver's.


Alignment, syspension and brake shop.
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  • catmandew answered 4 years ago
    10W-30 oil is thicker, both when cold (the first number) and when at operating temperature (the second number). Higher number is thicker.

    Since I don't know what kind of car you're talking about, or much of anything else about the circumstances involved, I would be hesitant to say it would be OK.

    With certain Variable Valve Technology engines, oil weight is critical to proper operation of the engine, and noticeable driveability symptoms could result.

    And yes MARTYN, there is such a thing as 5W-20 engine oil. In fact, it's probably the most commonly specified weight for vehicles currently being produced.

    re; Additional Details

    OK, well now we're getting somewhere at least, although I still don't know which engine you have. If it's the 2.3L MZR engine for example, thicker oil could definitely cause some problems. The S-VT system is one of the types of VVT that rely on the right weight of oil being used, to work properly.


    "Mazda S-VT — Continually varies intake timing and crank angle using an OIL control valve actuated by the ECU to control OIL pressure."



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  • Naughtums answered 4 years ago
    It is absolutely not OK. If it was OK, your owners manual would say it is OK. This isn't a 1972 Buick you are driving but a modern car built to modern tolerances.


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  • MARTYN answered 4 years ago
    You should only use the oil specified by the vehicle manufacturer.

    I've never heard of 5W-20, but the lower number, the "winter" rating, tells you how thin the oil is when cold. the higher number, how thick it is (its viscosity) when the engine is hot.

    Thinner oils are more efficient and improve economy.

    I wouldnt use an oil thats too thick at operating temperatures, unless of course its a very old engine.

    If it says use 5W-20 (is that correct?), then use that oil.


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