toyota vios specialist

Is it okay if I used 20w40 instead of 15w40 engine oil for vios 2011 model?

I am not a Toyota specialist, but the Vios, (known as Yaris outside of Asia), 1.5 L variable valve timing engines are designed for SAE 5W-30 engine oil. When you choose 20W-40 this means the oil flows poorly in cold temperatures and is generally a much higher viscosity oil, ie thicker. The hydraulics that work the VVT-i need thin oil. When they do not function correctly you can face high repair costs. The solenoid pistons that control the valve timing needs very clean, thin oil all the time. The worst thing you can do to these engines is let the oil become dirty, because this clogs the VVT-i filters and restricts oil flow. Using thicker oil just makes things worse. No it is not OK to use a SAE 20W-40 oil, and in fact using 15W-40 is problematic, unless you are prepared to soon recondition the engine. It can cause cam dephaser errors for out of range, not something you want in an interference engine. Use only the factory recommended synthetic ACEA A3/B4, API SL/CF 5W-30 lubricant and I would add, use a “synthetic” oil filter as well.