After passing its MOT I decided to treat my Daewoo Lanos to an oil & filter change at National Tyres. I assumed they would use 10w-40 semi-synthetic like they did last time but instead they filled it with
0w-40 Visco 7000 fully synthetic. I wasn't too concerned as it's a good oil and it does seem to start up from cold better & quieter. However, I've noticed that there appears to be less power when the engine is under load. For example, if I approach a steep incline and knock it down a gear I don't have the same amount of pull & response from the throttle like it did before. It is a high mileage engine (over 100k) but uses very little oil between changes but I'm wondering if the 10w-40 semi helped to give it better compression than the 0w-40 fully?