tl;dr version:
accidentally bought and used monograde petronas mach 5 SAE 40 in iswara.
what are likely adverse effects of this?

i recently serviced my old iswara (1998). I usually buy my own engine oil coz my mechanic doesnt stock the brand of oil I want.
in the past, i always use magnatec 10W40 for this iswara but my mechanic recently told me its too thin to protect my old engine so he recommended i switch to mineral oil - petronas mach 5 specifically.

so i went and bought a petronas mach 5 engine oil. since this is the first time im buying mach 5, i didnt really check properly what i bought.
turns out, i accidentally bought the monograde version, SAE 40. i only discovered it while i am preparing to buy another canister for my next service.

to be honest, i am quite happy with the oil, the car started fine and the engine runs cooler and smoother with less vibration than before which was a surprise to me. seems like a good move from magnatec to mach 5 monograde EO for an old magma engine.

but i am a bit apprehensive that my engine is not getting the protection it needs during morning starts. is this really a valid concern or is SAE 40 actually perfectly fine to use in Malaysia?