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Any one know about the mixing of engine oils

alan kearnalan kearn Posts: 911
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in General Discussion #1
I do my own oil changes (VW Polo 1.4 TDI PD engine) usingMillers recommended semi synthetic 505.01 oil and I have about 3 litres left from last year. Millers have now discontinued this type of oil replacing it with a full synthetic oil. My car takes around 4 litres of oil so can I mix the 3 litres of semi synthetic oil left from last year with about 1 litre of the new full synthetic oil that Millers now recommend for my next oil change.A alternative I presume would be to buy a different manufacturers 1 litre bottle of semi synthetic oil (to make up the 4 litres) required for my engine.
The bottom line I suppose is, can you mix semi synthetic and full synthetic oil



Thanks

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    Blackjack DavyBlackjack Davy Posts: 1,166
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    #2
    Generally the recommendation is don't mix them. Use all of one or all of the other.
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    howardlhowardl Posts: 5,120
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    #3
    If that was me I'd put a litre in in a bottle in the boot for topping up, if needed.
    keep the other 2 stored somewhere.
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    Chris FrostChris Frost Posts: 11,022
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    #4
    Have a think about what happens in garages when a car goes in for work that includes topping up the oil. Do you see garages with absolutely every make and grade of oil? Or do they just top up with whichever brand is carried in that big 205 litre drum in the workshop. :)

    Adding a higher grade oil as a top up won't be a problem unless the engine manufacturer specifically states "Do not use xyz type oil". Millers XF Longlife fully-synthetic meets or exceeds 505.01 API CF. This is the same spec as the semi-synthetic Millers XFE.

    If you're still worried then here's the answer.

    Take the Millers spec for their semi synthetic (API CF / 505.01 / Ford M2C 917A / ACEA B3) and go find a litre bottle of the same spec from a different brand. 3 litres of Millers + 1 litre of Mobil/Castrol/Gulf/Motul/Fuchs/whatever = 4litres of the same grade semi-synthetic. Gulf Tec Plus 5w-40 semi-synthetic engine oil would do. Happy days. :)
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    Waj_100Waj_100 Posts: 3,739
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    #5
    You can mix the semi synthetic with the 1 litre of fully synthetic, but the PD engine should have PD oil, like this....http://www.uk.commaoil.com/passenger-vehicles/products/view/177/DPD5L


    If a modern diesel engine has a Diesel Particulate filter (DPF) then you can only use an oil with low ash and that is compatible with DPF fitted vehicles.

    Using the correct oil nowadays is crucial to engines, as the owner of a car repair business it's a nuisance having to keep checking that I'm using the correct oil for the specific vehicle.
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    alan kearnalan kearn Posts: 911
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    #6
    Waj_100 wrote: »
    You can mix the semi synthetic with the 1 litre of fully synthetic, but the PD engine should have PD oil, like this....http://www.uk.commaoil.com/passenger-vehicles/products/view/177/DPD5L


    If a modern diesel engine has a Diesel Particulate filter (DPF) then you can only use an oil with low ash and that is compatible with DPF fitted vehicles.

    Using the correct oil nowadays is crucial to engines, as the owner of a car repair business it's a nuisance having to keep checking that I'm using the correct oil for the specific
    vehicle.

    The specification of the 1 litre of full synthetic oil I will be adding to the 3 litres of semi are here

    http://www.opieoils.co.uk/p-60252-millers-oils-xfe-pd-5w-40-semi-synthetic-engine-oil.aspx
    and here

    http://www.opieoils.co.uk/p-74058-millers-oils-xf-longlife-5w-40-full-synthetic-engine-oil.aspx

    it includes the 505.01 that is needed for TDI PD engines so it looks as though I will be OK mixing the two

    thanks
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