Stock engines are built with tolerances. So if you decide to use something other than the xW30 weight that Myvis are made for, it'll still work. Like 5W40 on a myvi or 20W50. But you'll notice significant strain on the engine or have poor FC or something like that.

But if you want to change to 0W30, 5W30, 10W30, 15W30 (no such oil) those are fine.

If your engine is balanced, built to spec and heavily modified, then the tolerances is probably a whole lot less. Changing to a weight that it wasn't designed for might overstress parts and cause premature wear.

Hmm.. not quite.

The gap between the piston and the cylinder walls are super thin. The thicker the oil the more effort the engine needs to push the oil through the oil channels and all. Some engines are built with very low tolerances. Too thick oil and the engine will seize. Kinda like how F1 engines use single weight oils and are fed intravenously hot into the engine otherwise it's too thick for the engine to start.

The stock Myvi K3VE isn't a low tolerance engine so it'll probably work without issues with 20W50. But why would you want to? Imagine the amount of effort needed to push that thick oil through, you'll experience power loss, sluggish performance and bad FC.

5W30 vs 5W40 isn't that much different in terms of weight. But 5W20 vs 5W40 is quite significant. Aiya, it boils down to your own judgment and wallet size. Can't afford good fully syn oils just buy the Perodua 10W30/5W30 semis. Those are actually quite good for normal cars and are cheaper. But shorten the OCI and that's it.

I've used that Eco Touring oil as well. I didn't like it. It's expensive, the car felt heavy and oddly enough the oil seemed to break down faster than expected (FC started getting bad and revving got really heavy). I'm doing a comparison with Perodua 5W30 silver and Pennzoil 5W30 fully syn.

Interesting, it's called "Dupont Krytox"? Is it an automotive grease?