In the previous issue, we showed you what the numbers and letters on the sidewall of your tire really meant. On this one, we are doing the same for engine oil. Engine oil, widely known across the country as “Mobil” acts like the blood of any vehicle, two-, four- or ten-wheel­ers. If it has an engine and wheels, chances are it needs Mobil to run. While petroleum acts as a means of propulsion, engine oil does every­thing else, from proper cleaning and lubrication to efficient usage of fuel.There’s a wide range of engine oils to choose from so it is difficult to know what type would be best for your vehicle. Thankfully, you never have to, because the vehicle manufacturers already know what oil you need when you go for your routine service and they use what is best for your ride. But it doesn’t hurt knowing a little more about the “Golden Blood” that makes the wheels go round.

 

Okay, let’s start with the basics. There are three core types of engine oils in the market: mineral, semi-synthetic and synthetic.

 

Mineral oil is the cheapest and is essentially a constituent of crude oil, produced after it is refined.

 

Synthetic oil is the most expen­sive, but for a reason. It has been engineered by scientists to work over a wide range of tempera­tures and conditions, while reducing drag on the engine to help reduce fuel consumption. It also actively cleans the engine’s internals as it’s pumped around.

 

Semi-synthetic oil is a blend of mineral and synthetic oil, the blend made basically to bring the price down.

 

Next is the most important and widely heard term when it comes to engine oil, “Viscosity”. This is the large numbers on a bottle of oil like 5W30 or 10w40. Simply put, vis­cosity is the ‘flowability’ of oil. Put another way, thin oil has low viscos­ity, while thick oil has high viscosity.

 

The viscosity of oil changes with temperature. When it’s cold, the oil will flow more slowly and when it’s hot, the oil will flow more quickly. However, in order to lubricate an engine properly the oil must be able to flow at a consistent rate through a broad range of temperatures.

 

To put this in perspective, imag­ine a bottle of ketchup, put it in the fridge (at roughly 1-3 degrees Celsius) for a few hours, then take off the lid and try to pour the ketchup out. It will start to flow but extremely slowly as the cold temperature has made it more viscous. Now take your bottle of ketchup and stick it in the oven for 20 minutes at 100 degrees Celsius then take the lid off and pour it out. It should flow out extremely easily. The heat has reduced the viscosity and allowed the syrup to flow more quickly.

 

The same thing happens with engine oil. If you live in Lukla and its -20 degrees outside, when you go to start your car’s engine, the oil inside it needs to be thin enough to flow and lubricate all the internal com­ponents as soon as you turn the key. Similarly, if you live in Birgunj and its 40 degrees outside and you’re driving in heavy traffic your engine oil needs to stay viscous enough to lubricate properly.

 

Most oils these days are multi-grade (multi-viscosity) and will have two numbers instead of one on the label separated by a ‘W’. Multigrades were first developed some 50+ years ago to avoid the old routine of using a thinner oil in winter and a thicker oil in summer. The numbers look somewhat like this: 10W-40

 

The first number followed by the letter W describes the viscosity of oil at low temperatures (the W stands for winter). The lower the number the thinner the oil. A thinner oil at low temperatures is good because it flows more easily and is therefore able to protect the engine when it is first started from cold. If the oil is too thick when cold, it will not circulate freely and will reduce fuel economy.

 

The second number describes how thick the oil is at the engine’s normal operating temperature. The higher the second number, the thicker the oil. If it’s too thin when hot, it may not protect effectively. If it’s too thick, you lose efficiency. The correct viscosity grade will be displayed in your car handbook.

 

Apart from this, there’s one more thing to engine oil. The oil speci­fications, which is the answer to what engine oil is best for you. Oil specifications define what type of engine a particular oil is suitable for and its performance against a range of criteria. There are a handful of specifications but we’ll only talk about OEMs (Original Equipment Manufacturers) as they’re most used in our country.

 

All OEMs have their own engine oil for their cars: Honda has its own, Volkswagen has its own and so on. So be advised that the oil you put in your car at the autho­rized service station is the best for you. Most OEMs publish lists of all the oils they have approved, so the consumer knows which prod­ucts are suitable for their vehicle if they want an oil change outside the service station. These approvals are especially important for cars under warranty. Usage of unap­proved oil will instantly render it null and void.