The Engine Oil Dilemma

It’s scorching hot in Delhi these days, and one day while I was on my way to the office, it was around 11:05 AM and the sun was directly above my head. My watch started vibrating, and I saw it was a reminder to drink water. At the same time, I noticed the temperature was 42°C. I ignored the alert because I was stuck in traffic that was moving at a very slow pace. I was surrounded by so many vehicles, and I could feel the intense heat all around me.

A thought suddenly crossed my mind: how much stress must these vehicle engines be going through while operating in such extreme temperatures? Some engines are water-cooled, some are oil-cooled, and some vehicles, like my scooter, are simply air-cooled with no external cooling hardware. It just relies on the natural airflow passing through the engine fins to cool itself.

I started wondering about the high-speed piston moving inside the cylinder, constantly creating friction between the piston and cylinder walls, which generates an immense amount of heat. In bumper-to-bumper traffic, if I’m cruising slowly at around 2200 RPM, then the piston is moving up and down almost 4400 times per minute, which is nearly 73 times per second. And it’s the engine oil that keeps all those high-speed moving parts lubricated at such high temperatures so that the engine components don’t reach their breaking point and fail.

That made me realize how important engine oil really is. This is why choosing the correct grade and good-quality engine oil for a vehicle is extremely important. However, engine oil grades can sometimes be confusing. For instance, my scooter manufacturer recommends a 10W-30 oil grade. The number “10” along with the “W” represents the viscosity rating in winter conditions, meaning how well the oil performs in cold temperatures. The smaller the number, the thinner the oil, and the better it performs during cold starts. The number “30” represents the viscosity rating at higher temperatures, specifically around 100°C. A higher number means thicker oil, which generally provides better lubrication and performs better in hotter conditions.

After analyzing the viscosity rating chart for the engine oil grade used in my scooter, I found that 10W oil provides good cold-start performance down to -25°C, meaning there won’t be any oil flow issues even at that temperature. That’s more than sufficient because Delhi’s temperature never drops that low; the average minimum winter temperature here is around 10°C.

Now, considering the “30” viscosity rating, the oil’s flow resistance at 100°C remains between 9.3 cSt and 12.5 cSt, which is considered normal and suitable for Delhi’s climate. However, the reason for my anxiety was that I’m pushing my 110cc air-cooled scooter to its limits. My daily commute to the office is around 43 km, which includes both bumper-to-bumper city traffic and highway riding. The total riding duration is almost 1 hour and 35 minutes, usually during noon when the temperature remains at its peak. So naturally, I started wondering how well the engine oil was actually performing under these conditions.

Considering my riding pattern, should I upgrade from 10W-30 to 10W-40, or should I switch to fully synthetic oil instead?

There are basically three types of engine oil: mineral, semi-synthetic, and fully synthetic. Although all three oils may maintain similar viscosity at 100°C, the real difference lies in how long they can retain their lubricating properties under extreme heat. Fully synthetic oil retains its properties for the longest duration, followed by semi-synthetic, and then mineral oil.

Currently, I’m using Motul Scooter LE MB 10W-30 4T motor oil, which is a semi-synthetic oil. So I was confused about whether I should upgrade to Motul Scooter Power 4T 10W-30 MB, which is fully synthetic, or move to a thicker 10W-40 grade oil instead.

Eventually, I ruled out the 10W-40 option. Increasing the oil grade to 10W-40 would make the oil thicker, which is beneficial at higher temperatures, but it would also put additional strain on my scooter’s stock oil pump, especially considering the scooter has already covered around 1 lakh kilometers. I might even have to think about upgrading the oil pump in the future. Additionally, thicker oil would slightly reduce fuel economy because of the increased internal resistance. The only major advantage would be improved lubrication at very high temperatures.

After weighing the pros and cons, I found more downsides to switching to 10W-40. So I came to the conclusion that I’ll continue using the manufacturer-recommended 10W-30 grade, but I’ll upgrade from semi-synthetic to fully synthetic oil. That way, the engine oil will retain its lubricating properties for a longer time under high temperatures, which suits my long daily rides much better. And perhaps during winters, I can switch back to semi-synthetic oil again.