Actually, multi-grade oil does still matter even in country like Malaysia. The "W" does not only indicate winter usage. A 15W-40 oil is about as thin as SAE 30 oil so it flow better than a SAE 40 oil at normal cold start temperature of around 30c but it stay as thick as SAE 40 oil at engine running temperature.

Most of the time, it won't happen in a short time but long term excessive wear on engine can happen during the first few seconds of engine cold start if the oil is too thick for a fast and smooth pump during cold start. This is especially true for a car that are not start often, for example, once every few days. Oil pump, filter and other key areas has to be taken into account as well. There are reasons when the car manual recommend a 5W-30 oil rather than a 10W-30 oil or SAE 30 oil despite all of it being a SAE 30 grade oil at normal engine running temperature.

This SAE 40 oil, like other monograde oil, are usually only used for older engine model and design or where engine condition are no longer at its optimum level or car that are up and running most of the time such as taxi for cost effectiveness reason.