Can You Mix 10w30 And 10w40 [You Must Know]

You use 10w30 but you run out of oil. Suddenly, you looked at a shelf full of 10w40 that has no use. So, you decide to top off with 10w40. But the question that arises in your mind is- would it damage the engine if I combine these oils? 

Fortunately, we are here to give the answer to your question- Can you mix 10w30 and 10w40? So, let’s dive deeper to explore the effects of mixing the two different viscosity oils. 

Can You Mix 10w30 And 10w40?

This is a controversial question. You will get mixed responses when you ask this question to the falk. Some of you encourage you to go mixing the 10w30 and 10w40 unless you live in freezing weather.

Even the oil mix of the synthetic and conventional blend will show you no harm to your engine. But it will be true until you mix only a quart of other oil to your usual engine oil. 

But, we recommend you not mix or blend 10w30 and 10w40. If you put together these oils, it will boost up oil pressure when cornering at high revs. Therefore, blending different oil grades may affect your car’s warranty and oil consumption. 

Therefore, it will be less practical to pour mixed oil into your engine if you live in warm weather as the 10w40 is thicker than the 10w30. 

In short, you can’t mix 10w30 and 10w40 oils unless you are in an emergency situation where mixing is the only option. To avoid this occurrence, ensure you have spare oils when you travel. 

What Happens If You Mix 10w30 With 10w40?

You already know that 10w40 is more viscous than 10w30. If you blend these two different viscosity grade oils and pour them into the engine, it will increase friction.

In other words, it may damage your car engine by increasing wear & tear. Therefore, an increase in oil pump load will occur if you mix those oils. 

Is It Ok To Put 10w40 In A 10w30?

No, it’s not ok to put 10w40 in a car engine that is designed for 10w40. You know 10w40 is more viscous than the 10w30. And the 10w40 oil is specially formulated to handle hot temperatures. So, the thicker oil like 10w40 flows easily and keeps enough viscosity to shield the skirts and bearing when the engine gets hot. 

On the other hand, 10w30 performs the best in cold weather. If you put 10w40 in an engine designed for 10w30, it will increase metal frictions and damage the engine. You can watch the video to learn more.


Does 10W40 hurt a 10W30 engine?

Yes, 10w40 will hurt the 10w30 engine. The 10w40 oil is thicker than 10w30, and it will increase friction if you put this oil into an engine designed for 10w30. 

What happens if you use 10W40 instead of 10W30?

The higher the number, the thicker or viscous the oil is. So, 10w40 is thicker than 10w30, and it provides better engine protection in hot temperatures. But if you use 10w40 instead of 10w30 in a 10w30 engine, it will just increase friction and oil pressure. Consequently, your engine will get damaged by friction.  

Can you mix 10W30 and 10W40 in a motorcycle?

Yes, you can mix 10W30 and 10W40 in a motorcycle. 

Is it bad to mix oil viscosity?

It is not advisable to mix different oil viscosity. If you mix different viscosity grades, it turns out to be a different product than what was in your engine or what you added. 

Can I mix 5w40 with 10W30?

Yes, you can mix 5w40 and 10w30 if the oils come from the same brand. Otherwise, you should avoid mixing oils as each brand uses different additives. 

Is 10W40 good for high mileage?

Yes, 10W40 is good oil for high mileage cars as this oil provides better engine protection in hot temperatures. 


Never try to combine 10w30 and 10w40 oils. You shouldn’t even use the same viscosity oil from different manufacturers. Each oil has unique additives and they don’t play together when you mix them. We recommend you always have spare oils in your car when traveling to avoid blending oils. 

About John M

John contributed as a technical head at an automobile company just 2 years after his post-graduation in Automobile Engineering. He loves to lead a free life, so he left his job & started blogging. Now, he does research on every automotive problem, part & product and seeks a better solution & best products & shares his findings with his readers to help them as well as to minimize their struggle.

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