Is there any difference between 15W-40, 10W-40 and 5W-40 in terms of cold start viscosity in Malaysia's weather?

I'm currently using 15W-40, it's actually diesel eo, recommended by the eo shop owner and is rated also to be used on gasoline engine. I know it's weird but these oil comes in large volume like 20L per "pail", my car requires quite about 6L of oil per oil change, which makes the oil change quite costly, so that helps a little. I change it every 5000km and a new filter every 10000km, and my mechanic also inspect the filter and he say it's very clean and nothing peculiar on it (mine is cartridge type filter, so it's every easy for him to inspect). So I think it's still fine *touchwood*.

I'm asking because I feel that especially during cold start, it "feels" like it takes awhile for the oil to flow through the engine and lube the parts, and the difference in idling sound is actually audible, very minute but still audible. I just want to ask if lower winter grade eo will actually make any difference during cold start to make sure the oil lubricate the engine as fast as possible at Malaysia's ambient temp. Just don't want any unnecessary wear and tear on the engine as my car is turning 26 this year, just want to make sure it will last "forever".

Thank you for the info, I guess I will try 10W-40 semi synthetic oil

Erm, you sure the eo used by the team is anything close to what they offer on the shelf? Just my 2cent, there's almost nothing on the car that are off the shelf.

I get the point, but what I’m trying to imply is, that shouldn’t be an indicator for quality products, the comparison is not on the same level. Not to say the product is bad, but just a little vague to assume it this way imho.

Yeah, I heard that many times from the commentary too.

I recognise this guy, I've watched many of his own videos on YT.

Fuel system cleaner (Techron) works for me, just a maintenance product to keep the fuel injectors happy.

The retail price seem to sit below Syntium line-up, not sure where it's made. My recent purchase of 2 bottles Syntium 3000E 5w40 are blended locally.

I don't have good access to Caltex station, so I just pump other brands nearby. Maybe, if your car has been using Caltex all the time, might not need the treatment. Supposedly all brands have their own blend of additives, so it's not really compulsory per say.

I tried because my car is very old, and I suspect few of the injectors not working perfectly. After one bottle Techron with one tank of regular 95, it improved the idling vibration I was having to a certain extent, and slightly smoother revs. But all these improvements have to view in relative aspects, since the car is old with other aging components, it cannot help if something is actually broken. If your car is quite new, good maintenance and no tangible issue that you can feel, it is likely a waste of money.

For my own cars, planning to use a bottle every 20,000KM. Bought mine at about RM50 a bottle from Caltex official store on Shopee.

Think occasional spirited drive/longer trips should keep the engine healthy