In my native Nigeria, the default engine oil for vehicles, trucks, motorcycles, and gasoline generators is the 20W50 weight engine oil — irrespective of what the manufacturer expressly recommends.
So common is this engine oil weight and so widespread is its use that it is often referred to by the motor savvy community as “the almighty 20W50”.
The argument by the mechanics and technicians there is that, the tropical weather calls for the thicker oil.
If as a vehicle owner, you’re not convinced and argue that your owner’s manual states that 0W20 (for instance) be used, you’re likely to get the standard answers, these folks who are known as Kazeems, have prepared and kept ready:
“Oga, that one no mean anything,” which translates to: “Sir, it doesn’t matter.”
Or, if they are feeling more generous with explanations:
“Oga, that 0W20 synthetic is for cold weather with snow…it is used abroad where the vehicle came from.”
Usually, this is all it takes for 20W50-weight engine oil to find itself in an engine that was designed with 5W30 or 0W20 oil weight in mind.
But, does this really matter? Should the manufacturer’s engine oil recommendations be followed to the letter or are the Kazeems right?
Before I answer this question, it is very important to clarify what the numbers and letters on the engine oil gallon (or can) mean in the first place.
What the Numbers and Letter on the Oil Gallon Mean
Typically, a gallon of engine oil has two sets of numbers on it, separated by a letter of the alphabet: 0W20, 5W15, 10W40, 20W50, 10W60, etc.
The first number is the ‘cold flow rate’ of the engine oil, its viscosity when cold or simply, its resistance to flow when cold — or during winter, which is where ‘W’ comes in.
The last set of numbers, after the ‘W’ signifies the ‘hot flow rate’ of the engine oil when hot or its viscosity at operating temperature.
The system for the assignment of these values to engine oil that meets the particular grade is handled by the Society of Automotive Engineers (SAE).
To put it simply, this is what this means, in layman’s terms: for an engine oil such as 0W20, when an engine with it (in) is started from cold start, the viscosity of the engine oil is basically ‘0’ — which enables it to be pumped very quickly from the engine oil sump to the topmost parts of the engine in a flash — ensuring protection to the critical valves and other moving metal engine components there, right from the word ‘go’.
Still using the example of the 0W20 weight engine oil, an amazing thing happens when the operating temperature of the engine is reached or generally, when the engine gets hot.
Instead of the engine oil thinning down, it instead, increases its viscosity, to the value of ‘20’ to better protect the hot engine and ensure that no metal-to-metal contact takes place.
This is the joy and beauty of multi-grade engine oils, especially those of the synthetic variant.
Why 20W50 is Bad for Your Engine
I’ve already told you that 20W50 is preferred in my native Nigeria and is the defacto engine oil ‘mechanics’ defer to in the name of the ‘hot weather’ Nigeria experiences.
What I’ve not told you yet is that the love for the 20W50 weight of engine oil isn’t limited to the Kazeems or the car owners in Nigeria — it is an almost global affair.
This is wrong…but exactly why is it so?
1. Increased Wear and Tear on Engine Components
As you’ve already seen from the lines above, lighter engine oil weight, on cold starts, gets to the top of the engine fast, protecting the valves and all critical parts such as the rocker arms and camshafts.
With a thick engine oil weight like the 20W50, the exact opposite is the case: on cold start, the thick oil takes time before it rises from the engine oil sump and into the oil pump for onward pumping to the engine.
This is worse, during winter or when conditions are generally cold.
When this happens, metal-on-metal contact takes place between the various moving components before lubrication from engine oil comes.
Increased wear happens and usually, strange noises are next.
2. Reduced Fuel Efficiency and Engine Performance
The clearances in modern engines are small — and are getting smaller by the day.
What this means is that engines are increasingly, being designed to specifically work at their peak with lightweight engine oil, making the strange theory, ‘the lighter, the better’ very valid in this case.
From 10W40, to 5W30 and now, 0W20 and below.
Using thick engine oil in these engines means challenges of proper flow and with this, a failure to properly protect the parts it ought to.
With partial metal-on-metal contact, the engine works harder to move the vehicle and this comes at a steep price: overall lower efficiency and abysmal fuel efficiency.
Low MPGs and the feeling that you have your brakes binding isn’t exactly what to look up to, in this age and time.
3. Unnecessary Stress on the Oil Pump
The oil pump of a make and model is designed to brilliantly handle engine oil specifically designed for such a make and model.
While thicker (and lighter) weight will still work, in the case of the former, it will create serious pressure on the pump, causing it to work harder than it was designed for, under varying conditions.
It’s like what the heart needs to do when presented with a super large body.
It’s thus not uncommon to see engine oil pumps failing at as early as 50k miles or even less — in such conditions.
When is 20W50 (Ever) Appropriate?
The above said, 20W50 isn’t completely ‘bad’ engine oil: there are many instances where its use is ideal and even advised:
First, old(er)/classic vehicles designed with thicker oil in mind and impressive clearances in their overall engine design.
Second, abused engines that are already burning oil (the thicker oil slows down the burn rate).
Third, new(er) high-performance vehicles that are designed to take such thick(er) engine oil (for reference, the 8.0-liter, quad-turbocharged, W16 cylinder Bugatti Veyron takes SAE 10W-60 as standard engine oil weight).
Fourth, instances where you deliberately set out to get terrible gas mileage, cause fast engine component wear down, and importantly, are very eager to reduce the life span of the vehicle as much as possible.
If the above points do not reflect your reality, you’re better off using the oil weight your manufacturer expressly recommends.
Choosing the Right Engine Oil
Choosing the right engine oil weight for your vehicle boils down to understanding your vehicle’s requirements and following strictly, the manufacturer’s guidelines.
These requirements are written in the owner’s manual, is available in repair manuals (specific to your year and model), and on most brands, is also available on the engine oil cap.
If you’re still unsure, a quick search online is better than risking your engine with the wrong oil weight.
Conclusion
Choosing the right engine oil weight for your vehicle is critical if you’re going to get the vehicle to serve you for any reasonable amount of time and return good gas mileage during such a time.
In doing this, ignore the ‘counsel’ of roadside quacks who make the case for the thicker 20W50 for modern engines, citing harsh weather.
If you’re not driving a Bugatti Veyron, you probably have no business with 20W50 (heck, even a Veyron takes 10W60 — careful not to hurt itself while cold) even if you’re living in the hottest place on earth, Death Valley.
Exceptions exist, however: abused engines, classics, and vehicles designed specifically to take that engine oil weight.