Thickest Motor Oil: Details & Comparison

A vehicle user must know which is the thickest oil. Knowing this answer to the question will benefit you overall. Let’s get straight to the answer without further ado. In a word, 40w-70 is the thickest motor oil on the market.

Today’s discussion will talk about the use of the thickest oil, its pros and cons, and some other related issues. So without delay, get to the main discussion. 

thickest engine oil for car

What is the thickest motor oil?

Now we will know about the identification of 40w- 70. Here, the viscosity of the oil is determined by the number 70. On the other side, the viscosity in winter conditions is identified by the number 40.

In racing, you can use 40w-70. Diesel engineers tend to use our oil at the right rate. This thickest oil for car is perfect for this. The temperature and multigrade viscosity motor oils can perform. In the end, we have been able to know the answer which motor oil is the thickest.

What does engine oil viscosity mean?

The most important factor in engine oil usage is its viscosity. Correct engine oil viscosity is very important because it determines the engine’s operating temperature thickness and winter rating. The viscosity of engine-based oils varies. For example, the maximum working viscosity is 70, and the maximum winter rating is 40W, and this is for fat motors.

For example, oils with high operating viscosity perform best at hot temperatures, while oils with low operating viscosity perform best at cold temperatures. Oil viscosity rating is very important for an engine to run well. So there is always an operational rating of viscosity.

Comparison of oil based on viscosity

The advantage of low-viscosity full oil is that it works better in cold weather, i.e., it keeps the engine oil flowing in cold weather. Again, the advantage of a higher-viscosity oil is that higher-viscosity oil keeps the engine better by forming a thicker layer between the engine’s moving parts and maintaining a higher level of lubrication at higher temperatures.

Some units are used to measure viscosity. For example:

  • PI (poseable)
  • CST (Centistokes)
  • 10-6 Rains (lb s/in2)

The viscosity of engine oil is variable, i.e., it is not uniform all the time. The viscosity of engine oil is variable, and it changes depending on weather conditions. Because its viscosity is one in hot weather and the viscosity in cold weather is different; that is, it depends on the weather.

Grade  Oil Density  Oil Viscosity  
20W50  872 kg/m3  166 cSt  
15W40  866.3 kg/m3  105.1 cSt  
10W30  865 kg/m3  69 cSt  
10W40  865 kg/m3  94 cSt  
5W30  860 kg/m3  64 cSt  
5W20  858.4 kg/m3  64.8 cSt  
5W40  848.3 kg/m3  90.9 cSt  

Relative density (in kg/m3) and viscosity (in centistokes) levels of thick engine oil should be observed. Based on the temperature of the oil in the engine, it should have a density reading of 60 degrees F and a viscosity reading of 100-104 degrees F.

How to tell the thickness of motor oil?

Oil thickness can be calculated based on the viscosity of the oil in the engine. A “W” with a number on one side followed by a dash and another number is called the rating. For example, “85W-140” is the thickest gear oil for motor engines. With this, the thickness and viscosity of the oil in the engine can be determined.

The number on the right (40) is the viscosity, on the other hand, the number on the other side of the dash is used to determine the thickness, and the number on the left (15) is used to indicate the Winter or W rating. A lower W number indicates better performance than a higher number, and it rates the engine’s performance at cold temperatures.

thick oil for cars

What are the pros and cons of 40w70?

Everything has pros and cons, just like 40w-70 has both pros and cons. Before using the thickest oil, 40w-70, in an engine, it is important to know its pros and cons to understand how compatible and suitable it is for your engine.


40w-70 has a number of advantages, such as:

  • 40w-70 – It has a higher performance and a higher level of protection, it can provide a higher viscosity level of oil in the engine, and the higher viscosity of motor oil helps your car perform better.
  • The thickest oil, 40w-70, keeps the oil viscosity in the engine and helps to avoid engine damage.
  • It helps maintain the oil level of your engine and keeps the oil pressure and viscosity in the engine at the right level.
  • 40w-70 This limits the need for refueling, which helps reduce oil consumption, and in addition to reducing costs, it helps keep the engine running smoothly by keeping the oil pressure constant.


Along with the advantages of the thickest oil, there are some disadvantages. The disadvantages are:

  • Sometimes it causes damage to the engine if it is accidentally used for the wrong engine.
  • It is not adaptable to all types of weather, i.e. it cannot operate the engine properly in cold weather.
  • Another disadvantage is that it is thick, which does not transport heat properly to different parts of the car engine.

Which motor oil is the thinnest?

Viscosity is the most important factor in engine maintenance. So to keep the engine in good condition, one should know about viscosity. The lowest working viscosity of engine oil is the thinnest. SAE 16 (single-grade motor oil) is the thinnest oil in terms of operational viscosity.

0W-16 is a multigrade motor oil that is the thinnest overall for your vehicle’s engine, and it will give your engine the best performance at cold temperatures and has the lowest viscosity rating at operational engine temperatures. It is very important to match the oil viscosity with the engine. Engine performance also depends on proper engine oil viscosity keeps the engine running smoothly and reduces excess oil consumption. For this reason

thicker oil for older engines motor oil thinnest to thickest 60w oil.

Read Also : 0W20 instead of 5W30


Q. Which oil is thicker, 5w30 or 10w30?

Both the 5W-30 oil and the 10W-30 oil have a viscosity rating of 30. Since the viscosity rating is the same, look at the number before the “W” to determine the thickness accordingly. 5W-30 engine oil has a five winter rating, and 10W-30 engine oil has a 10 winter rating, but being 10 larger, it is thicker than the other. And it helps keep your engine running smoothly.

Q. Which oil is thicker, 20w50 thicker, or 10w40?

Both 20W50 motor oil and 10W40 motor oil are thicker. But 20W50 is thicker than 10w40. Because the viscosity of grade 50 is higher than grade 40. And it can protect the engine more than the other. Sometimes it causes damage to the engine if it is accidentally used for the wrong engine.

Final thoughts

After reading our article, you must have understood which is the thickest oil. Knowing this information will help you overall because the use of thick oil for vehicles is as important as it is necessary to calculate it correctly. At the end of the day, hopefully, your vehicle’s engine will last longer and save you money. Be aware of using the thickest oil and ensure the durability of your engine.


Rio is a car & motorcycle mechanic who is working with different kinds of problems relating to oil and grease. He is also a passionate technical writer.