I have a Toyota Yaris 1.3 VVT-i with 2SZ-FE engine. The car has 100K of mileage (I recently bought it with no service history). Most importantly, its check-engine light is on for "catalytic converter below threshold", which has also appeared in the MOT for the past 2-3 years.
I looked for Engine oils for this car, and based on suggestions on different websites, Castrol Magnet A5 and/or A5/B5 is the best choice. However, I've read in another post that the choice of oil (C3 vs A5, etc) should be made based on whether the car has a Catalytic converter.
My car does have a catalytic converter, but it is performing poorly, and I don't want to spend hundreds of ££ to replace it on such an old car. The question is: does picking a specific engine oil help improving the Catalytic converter performance for the MOT test?
Also, what engine oil is best for my car in its current situation?