The motor oil is a necessity to run any engine because without the lubrication provided by it, moving engine parts would collide with one another and cause wear. To cater to sludge, foaming, temperature cooling, acid neutralization as well as wear & tear, motor oil contains different additives.
Similarly, the viscosity of an oil is maintained by its viscosity modifier, these modifiers are made up of polymer compounds and expand to nullify the effect of oil thickening when the temperature increases.
In the Multi-Grade system of viscosities, there are two numbers; the first one is written before ‘W’ representing the cold temperature viscosity while the other one is written after ‘-’ showing hot temperature viscosity.
This article is focused on two such multi-grade viscosities i.e., 10W-40 and 10W-30, that what will happen when the second one is replaced by the first.
Difference between 10W-40 and 10W-30
We have talked about the concept of cold and hot temperature viscosities in the introduction, now using that same concept we can see that the cold temperature viscosities of both these oils are ‘10’ as they are placed before ‘W’.
But the difference lies in their hot temperature viscosities as the one to replace has the hot temperature viscosity of ‘40’ while the one to be replaced has ‘30’.
It should be clarified here that we need a low viscosity at lower temperatures and high viscosity at higher temperatures to get a better performance out of the oil.
It is evident that the 10W-40 has ten grades higher hot temperature viscosity than its counterpart 10W-30, making it a better performance oil in summers.
Whereas in terms of cold temperature viscosity there is a tie between them since both have the same viscosity grade at low temperatures.
Deciding which Grade Oil to use
As discussed earlier, the oil with lower cold viscosity and higher hot viscosity is considered better but it will not be the efficient one in all cases.
Here we have gathered all the factors which one must consider when trying to choose which viscosity grade oil to use.
Each oil comes with a certain temperature range recommendation for the buyers to decide which one to use.
In our scenario the recommended temperature range of 10W-40 is from -25° to 40° C, on the other hand, that of 10W-30 is -25° to 30° C.
In short, we can say that if you live in a moderate climate region then 10W-30 is favorable for you but if the extreme ambient temperature reaches up to 40° C, then choose the 10W-40 grade oil.
The manufacturers of the car engine know the extent of their product and are well aware of the environmental conditions their vehicle is to be used.
That is why they recommend the best possible grades of oil to be used in that engine.
This information is shared with the customers in the Owner’s Manual, if it is unavailable, you can search the information on their website or even consult the company online through customer service.
The grade recommended in the owner’s manual is undoubtedly the best fit for your engine.
If for some reason you cannot consult the owner’s manual, then you may want to look at some other options.
The most common hand rule of the oil is that if you want to drive in a colder region go for the oil with the lowermost cold temperature viscosity and for hotter regions, an oil with the highest hot temperature viscosity should be selected.
The blend of oil also matters a lot since there is a lot of difference in the performance of same-grade oils with different blends.
Synthetic is the strongest with the highest capacity to hold additives, Semi-synthetic is good with moderate performance while the conventional are least effective of all.
Normally, a 10W-40 is stronger than 10W-30 but a conventional 10W-40 oil is weaker than the synthetic 10W-30 oil.
Therefore, you must also consider the blend of oil when selecting which grade to use.
There are a lot of oil brands in the market and some of these oils that claim to be of a certain grade may fall short of the mark in terms of performance.
In order to avoid this look for the API and ILSAC-approved oil as they classify oils according to their performance.
Same grade oils with various levels of API and ILSAC certifications will not perform the same, hence also consider this when buying oil.
Last but not least is budget which dictates most of our decisions in life, the same is true for motor oil purchasing.
We recommend you avoid both the highly cheap and expensive oils as the cheaper ones will not have all the necessary components and the expensive ones will not give better value for money.
Find a compromise between the price and performance to land the best deal possible.
What if 10W-30 is substituted by 10W-40?
Coming to our main question of the topic since we now have the knowledge of oil grades and an understanding of how to select an oil grade, it’s easy for us to answer this question.
The answer is yes, you can swap the 10W-30 grade oil with the 10W-40 one.
To justify this answer, since the cold temperature viscosities of both these oils are the same hence there be no issues in using 10W-40 instead of 10W-30 in wintry weather.
The difference is in hot temperature viscosities, but it too will, poses no threat as the substitute 10W-40 has higher hot temperature viscosity than that of the 10W-30 grade oil.
In simple words, the temperature range covered by 10W-30 oil fall within the temperature range of 10W-40 oil.
That is why it is possible to substitute 10W-30 with 10W-40 but there are some mild consequences to it which are covered in the next heading.
Consequences of substituting 10W-30 with 10W-40
There are no dire consequences except for some negative effects which are mentioned below:
- Higher prices have to be paid for the 10W-40 grade oils as compared to the price of 10W-30 ones.
- If a conventional blend of 10W-40 is used instead of synthetic 10W-30, then it will perform poorer.
- The performance will decrease if the lower API and ILSAC certified oil is used in place of highly certified 10W-30 oil.
- 10W-40 will not perform efficiently if it is not recommended in the owner’s manual.
- The full potential of the 10W-40 cannot be utilized since it’s made for hot weather and the 10W-30 is for moderate one.
Mixing 10W-40 with 10W-30
Although it is possible to use 10W-40 grade oil with 10W-30 one, there are some conditions that must be fulfilled.
Those are; firstly, the blend of both these oils must be the same, dissimilar blends do not work well with each other.
Secondly, the chemical formula of the oil must be the same, meaning both have a similar method of manufacturing.
Thirdly and lastly these oils must use similar compounds as additives even though in different ratios e.g. titanium is a very uncommon anti-wear additive if one oil is using it then the other must also have it.
To ensure these conditions simply use different grades of any similar type of oil class of the same brand.
If these conditions are not meant the oils could end up canceling each other’s effects and we will get a negative effect on the overall performance.
We can conclude our article by saying it is very feasible to use 10W-40 instead of 10W-30 but there is no point in having to pay extra for the product who’s some potential is unusable as it is made for up to higher temperatures of 40 degrees Celsius while the other one is good for temperatures up to 30 degrees Celsius.
That is why we do not recommend substituting these two oils unless you have no other choice.