5W-20 and 0W-20 both represent the SAE multigrade classifications which are allocated to engine oils. While 0W-20 grade oils are designed for colder climates, the 5W-20 grade oils are manufactured keeping in mind moderately hot climates.
5W-20 grade engine oil is more common as it is necessarily used for moderate climate regions.
It has a high thickness due to a higher cold viscosity grade, making it more resistant to flow.
It is manufactured with either conventional or mixed base oils, which render it less stable.
Such base oils also don’t allow for higher quantities of bases and additives to exist in the oil.
This oil can be used for a decent interval of time and is cheaply available.
On the other hand, 0W-20 excels in most of the parameters due to its lower cold viscosity grade, making it thinner and easier to flow.
It’s made up of either fully or partially synthetic base oils, hence it is more stable and could carry higher amounts of bases and additives.
This increases its performance in almost all fields.
There is however one drawback, that this oil costs a lot.
|Characteristics||5W-20 Grade Viscosity Oil||0W-20 Grade Viscosity Oil|
|Stability||Less Stable||More Stable|
|Blends||Partially Synthetic or Conventional||Fully or Partially Synthetic|
|Flashpoint Temperature (approx.)||224° C||230° C|
|Viscosity Index (approx.)||173||120|
|Suitable Temperature Range||-25° – 25° C||-40° – 20° C|
|Oil Change Interval (miles)||Up to 10,000 max||Up to 15,000 max|
|Cost||Relatively Cheaper||Relatively Costlier|
Oil Blend Type
Generally, there are three types of oil blends: Fully Synthetic, Partially Synthetic, and Conventional.
Conventional oils are refined from crude oils and additives are added to improve their performance while Full synthetic oils are made up of synthetic base oils which are modified along with typical hydrocarbons.
However, Semi-synthetic oils are a blend of both conventional and synthetic oils.
Considering this, the viscosity grade 5W-20 is made up of conventional or partially synthetic base oils.
Whereas the 0W-20 grade can only be achieved through fully or partially synthetic oil blends since it requires better cold performance which is not possible with conventional oils.
SAE (Society of Automotive Engineers) is responsible for allocating the viscosity grades to different oils for standardization.
In this case, both these oils are multi-Grade oils meaning that they are separately tested at both hot and cold temperatures to obtain their respective viscosity grades.
Universally they are marked by the “XW-X” pattern where ‘X’ are numbers and X before ‘W’ represents cold temperature viscosity grade (Winter) while the ‘X’ after ‘–’ shows hot temperature viscosity grade.
- Cold Viscosity
The cold viscosity of 5W-20 is ‘5’ while 0W-20 is ‘0’.
- Hot Viscosity
The hot viscosity grades of both 5W-20 and 0W-20 are ‘20’
Oil Composition and Chemical Strength
The chemical composition of oils mainly depends upon the nature of base oils whether they are synthetic, partially synthetic, or conventional.
Synthetic oils are chemically more active which makes them dependable and more stable than other oils.
Similarly, semi-synthetic oils are stronger than conventional but are less effective than their synthetic counterparts. Conventional oils are the least reliable in terms of stability and strength.
0W-20 being fully or partially synthetic is more chemically stable than its competitor 5W-20.
The synthetic base oils allow a higher tendency to hold additives than partially synthetic or conventional oils. Through this logic, we can conclude that the 0W-20 can hold higher quantities of additives than the other oil.
- Viscosity Modifiers
Viscosity modifiers are polymer molecules that are heat-activated and lying dormant inside the oil. Only when the temperature rises, do these molecules expand and increase the viscosity of an oil. The 0W-20 has a higher quantity of viscosity modifiers.
Like chemical strength, the physical parameters are also controlled by the additives and viscosity modifiers.
The most important physical parameters of oil are its flash point temperature and viscosity index.
The flash point is the temperature at which the minimum amount of oil vapors could burn for instance whereas the viscosity index is the representation of the resistance an oil has against the temperature-led changes in its viscosity.
- Flashpoint Temperature
The oil with higher resistance to extreme temperatures will have a higher flashpoint since its molecules could not easily break down. 0W-20 with a higher chemical strength offers better resistance to vaporization. That’s why its flashpoint temperature is somewhat higher than the 5W-20.
- Viscosity Index
The oil with a higher quantity of viscosity modifiers will be better at resisting changes in viscosity due to temperature fluctuations. Even though the synthetic base oil of 0W-20 holds a greater number of viscosity modifiers, they have to maintain the viscosity for a greater range of temperature i.e. -40° to 20° C. This allows the 5W-20 to take the lead in terms of viscosity index as its moderate numbered viscosity modifiers only maintain the viscosity between -25° to 25° C.
After analyzing both the viscosity grades physically and chemically let’s see how they end up in real-world conditions.
- During Cold Climate
As mentioned earlier the cold viscosity of 5W-20 is ‘5’ while that of 0W-40 is ‘0’.
This helps the latter to take the lead on its rival in terms of a cold start. Its pour point temperature (freezing point) is also lower than the other oil, making it more suitable for the cold climate.
Its lower cold viscosity helps it to flow smoother and quicker, resulting in better engine performance and power retention.
- During Hot Climate
On paper, both have an equal ‘20’ viscosity rating in hot conditions but there is more to it.
Since the base oils of 0W-20 are synthetic (Fully or partially) it gets an edge over its peer in extremely hot conditions as well.
Its base stocks allow for a greater capacity to hold additives which helps it fights better against sludge besides engine wear and tear at high temperatures.
Fuel economy is improved by ensuring three things, firstly the oil has a low thickness at cold temperatures (lower pour point temperature), secondly, the oil has a high thickness at hot temperatures (High Viscosity), and finally, the oil has adequate detergents and anti-wear additives (for running engine smoothly).
By evaluating both these oils for different characteristics the 0W-20 was found better fulfilling the above-mentioned conditions.
That’s why its fuel economy is better than that of 5W-20.
We can physically mix any two oils of 5W-20 and 0W-40 grade viscosities but the results are not what one expects.
It is foolish to assume that mixing such two oils will give a better hot and cold performance, on the contrary, it’s highly inadvisable.
The reason is that both have separate chemical base oils and additives which don’t work very well together. Using any two of these oils separately will give a far better performance than both of these combined.
Any oil is usable as long as it has active additives and maintains a basic PH throughout.
Although a considerable amount of all these compounds is present in all oils, the first one to usually end up is its base.
During the combustion process, the engine produces a lot of acids which can corrode the metallic engine parts.
To counter this the engine oil contains bases that react with acids to nullify them and as they do their quantity eventually decreases.
The minimum PH up to which the oil can be used is ‘1’ below which it is unusable.
As discussed earlier synthetic oils (both fully and partially) have a higher capacity to hold additives which also include base additives.
Hence any 0W-40 oil will generally give a higher mileage than its 5W-20 grade counterpart.
Deciding which Grade Oil to use
One should not jump to a conclusion in deciding which grade oil to use in his/her car as there are several other considerations to make as well other than just relying on the performance indicators.
- Owner Manual
The best way to decide which grade engine oil is best for you is to consult your owner’s manual which comes with the new cars.
The grade recommended there is undouble best for your engine as the engineers perform several tests before advising anything.
The reason is that no one knows the thing better than the one who designed it.
Hence, in short, follow the manual.
- Ambient Temperature Extremes
In case you are buying a secondhand car and there is no manual available, then another method is recommended i.e. to choose the grade which is best suitable for the location you are planning to use the vehicle.
For deciding simply check the extreme hot and cold temperatures of that areas and buy the one which best fits the temperature requirements.
In this comparison, the 0W-20 is good for cold climate regions while the 5W-20 best suits the moderate temperature regions.
Negative Impacts of using the wrong viscosity oil
One might be tempted to use the wrong viscosity oil in his/her engine.
In such a scenario following problems could occur
- Damage to the engine at cold start
- Higher fuel consumption
- Lower mileages
- Lesser fuel economy
- Unoptimized engine operation
- Unsmooth oil flow
- Low oil pressure etc.
Hence use the one which is either mentioned in the owner’s manual or best suits the temperature conditions of your area.
Synthetic oils are always costlier since they are pricey to produce due to which such oils cost a lot. In the following condition, 0W-20 is either fully or partially synthetic making it hard on the budget and since the other oil (5W-20) has conventional or mixed blend nature, therefore, it is light on the pocket.
However, we must consider the stability and reliability offered by the first oil not just its price.
|Sludge Removal Capability||Lower||Higher|
|Hot climate Performance||Lower||Higher|
|Cold climate Performance||Lower||Higher|