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There are many reasons for that. One of them is bad piston rings or sticky rings (you can use special additives to fix it). Another one is bad valve seals (again special additives can fix it too). In some cases the additives cannot fix such problems you have to replace failed parts.

PS: When you use the additive which changes the oil viscosity make sure that you don't harm the engine (in cold parts of USA oil with high viscosity will damage engines).

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16y ago

What else can I help you with?