Mineral , semi synthetic or fully synthetic?

[oj88]

My old 2011 Fiesta is using Shell Helix in the casa since day 1 and I always notice a slight oil burn smell (sensitive nose) after around 4000 RPM. I thought it is the norm so I don't usually exceed that RPM unless I don't have a choice. Around a year ago, I DIY and bought Amsoil in Lazada with Bosch filter and just did the oil change in Motech since it is just hundreds of meters away from our house. I did not expect much but lo and behold, initially I thought 4000+ RPM without any burning smell is cool. The engine sound is better too, maybe due to its Yamaha roots it's trying to encourage you to rev up more and more so I ended up 5000 max then one day hit 6000 RPM red line (yeah you won't notice it). Still no oil burning smell and no ill effects so far, did not expect me enjoying the old car 7 years after. My FXT is fed with Motul and can't wait to switch to Amsoil after warranty expires. Tried to but it is a long story. Was also not surprised that Amsoil won the Project farm youtube channel oil championship mid this year. Now I wonder how Amsoil will perform in a K24 engine revving 7000 RPM. I bet it will be more fun than my two cars combined lol.

Motor oil smell in the cabin? Impossible.

Apart from the combustion chamber, the engine is pretty much a closed system. The little oil it ejects as a by-product of blow-by is ingested back into the combustion chamber to burn off. If you have an issue with oil consumption, it'll be out your vehicle's tailpipe. There is no way it can enter the cabin. And if you have a problem of exhaust gas coming into the cabin, you'll be smelling exhaust fumes before you smell the burnt oil.

The odor is likely from adhesives, upholstery or materials around the area where the cabin floor meets the firewall. That's usually where the hot exhaust pipe from the engine or even the cat passes through in close proximity. That area is also close to A/C intake and so it can easily be mistaken to be an issue with the A/C. You see, running at a sustained high RPM makes the exhaust pipe very hot... even glowing red in extreme situations.

I noticed the same with my then 07 Civic FD. If I do some spirited or aggressive driving (4-6k RPM), I will immediately smell trace odor of something burnt coming out of the A/C vents. Scared me in the beginning. Eventually, as the adhesive or material cures, the odor becomes less and less prominent. By the time I sold the vehicle 7 years later, the odor was gone.