If you have been buying engine oil for a while, you have probably come across 20W-50. And if you have an older car, there's a good chance a mechanic has told you: "Use 20W-50. Your engine is old now." But is that actually a good rule? Why do some engines use 20W-50 while others require 5W-30 or 5W-40? And does using a thicker oil really mean your engine is getting better protection?
Let's talk about it. So, what exactly is 20W-50? The numbers are the viscosity classifications of the oil. The 20W relates to its low-temperature viscosity performance, while the 50 is its higher-temperature viscosity classification. You don't necessarily need to memorize all the technical details. The important thing to understand is that 20W-50 is a relatively higher-viscosity engine oil grade, particularly compared with oils such as 5W-30 and 5W-40.
And that is where the conversation gets interesting. Why was 20W-50 so popular? For many years, 20W-50 was a very common engine oil grade, particularly in older vehicle applications. Older engines can have different designs and lubrication requirements from many of the newer engines on the road today. Depending on the engine, a higher-viscosity oil may be exactly what the manufacturer intended.
So when an older car has been running on 20W-50 for years, there may be a perfectly good engineering reason for it. But this doesn't mean: Old car = 20W-50. That's too simple. What about engine wear and clearances? This is one of the reasons you shouldn't choose engine oil based only on what another driver is using. Inside your engine, there are very small clearances between moving components.
The oil needs to form an appropriate lubricating film between those surfaces while still circulating properly through the engine. As an engine wears over a long period, those clearances can change. This is partly why you hear people talking about thicker oils when discussing older engines. But the correct oil still depends on the particular engine and what its manufacturer specifies.
Why do mechanics sometimes recommend 20W-50 for high-mileage cars? This is probably the most common reason people switch to 20W-50. An older, worn engine may start consuming more oil. You might notice that you have to top up the oil more frequently than before. Sometimes, a higher-viscosity oil can reduce the rate of oil consumption in a worn engine. But here's the part that shouldn't be ignored: The thicker oil hasn't necessarily fixed the engine.
If the real problem is worn piston rings, valve seals, gaskets or another mechanical issue, changing the oil grade doesn't repair those components. It may simply reduce the symptom for a while. So if your car suddenly starts consuming plenty of oil, don't just say: "Let's use thicker oil." Find out why. Is thicker oil better? Not automatically. This is probably the biggest misconception surrounding engine oil.
Some people believe: 5W-30 = thin = weak 5W-40 = thicker = stronger 20W-50 = thickest = strongest But engine oil doesn't work that way. Your engine isn't asking for the thickest oil you can find. It's asking for an oil that provides the right viscosity and performance characteristics for its design. An oil can be perfectly good and still be the wrong choice for a particular engine.
What about Nigeria's hot weather? This one comes up a lot. "Nigeria is hot, so why are people using 5W-30? Shouldn't everybody be using 20W-50?" Not necessarily. The temperature outside is important, but it isn't the only thing that determines the correct oil. Engine manufacturers consider the engine design, lubrication requirements and operating conditions when recommending oil grades.
So don't switch to 20W-50 simply because the weather is hot. Can a modern car use 20W-50? It depends. Some modern engines may have 20W-50 listed as an approved option, while others may specifically require a lower-viscosity oil. Modern engines can have very specific lubrication requirements, including requirements related to fuel economy, turbochargers and emissions-control systems.
So the fact that 20W-50 works perfectly well in your friend's older Toyota doesn't mean it's suitable for your newer car. Check the manufacturer's recommendation. What about petrol and diesel engines? 20W-50 isn't restricted to one type of engine. There are 20W-50 oils formulated for different petrol and diesel applications. But the 20W-50 number alone isn't enough to tell you whether the oil is right for your vehicle.
You also need to look at the relevant performance specification and manufacturer requirements. Two different 20W-50 oils can have different formulations and approvals. So when does 20W-50 make sense? Depending on the manufacturer's recommendation, it can make sense for: * Certain older engine designs * Some high-mileage engines * Engines designed for higher-viscosity oils * Certain demanding applications * Petrol or diesel engines where the required specification allows it The key word is "allows."
Don't use the list above as a reason to change your oil. Use your vehicle's actual requirements. A few common 20W-50 beliefs "Every old car should use 20W-50." Not necessarily. "20W-50 is better because it's thicker." Not automatically. "20W-50 is the best oil for Nigeria." There is no single oil grade that is best for every vehicle in Nigeria. "If my engine is consuming oil, just use 20W-50."
That may reduce the symptom in some cases, but the underlying problem should still be investigated. And don't forget the oil quality Two oils can both be labelled 20W-50 and still have different performance characteristics. Look beyond the viscosity grade and check the specifications required by your engine. A properly formulated engine oil should be designed to provide things such as wear protection, oxidation resistance, deposit control, engine cleanliness and stable performance throughout the recommended service interval.
Brands such as Total, Mobil, Castrol, and Lukoil Lubricants offer different engine oil grades and formulations for different applications. But the same rule applies: Choose the product that matches your engine's requirements. The simple takeaway There's nothing wrong with 20W-50. It remains a useful engine oil grade for vehicles and applications that are designed or approved for it.
The mistake is assuming that thicker automatically means better. Your friend's car may love 20W-50. Your car may require 5W-40. Another person's car may require 5W-30. And all three can be perfectly correct. So before your next oil change, don't just ask: "Which oil is thicker?" Ask: "Which oil does my engine actually require?" What oil are you currently using in your car? 20W-50, 15W-40, 5W-40, 5W-30 or something else?
And if you've ever switched to 20W-50 because your car was getting older, did you notice any difference? Let's hear from the Nairaland mechanics and car owners. 😄
