Engine oil viscosity, or thickness, is one of the most important factors in choosing the right oil for your vehicle. Using the wrong viscosity oil can lead to serious engine problems and damage over time. Thicker oils typically provide more protection for your engine, but thinner oils have benefits too depending on your climate and driving conditions. This article will explain what oil viscosity means, what the numbers on oil weights mean, and when you might want thicker or thinner oil for optimal engine performance and longevity.
| Oil Weight | Typical Viscosity | Best Use Case |
| 0W | Thinnest oil | Extreme cold weather |
| 5W | Thin oil | Cold weather |
| 10W | Medium thin oil | Moderate/varying weather |
| 15W | Medium thickness oil | Warm weather |
| 20W | Thick oil | Very hot weather |
| 25W | Extra thick oil | Extremely hot weather |
Table of Contents
What is Oil Viscosity and Why Does it Matter?
Oil viscosity refers to how easily oil flows at certain temperatures. The viscosity measurement is known as the “weight” of the oil. Oils with higher viscosity (thicker oils) tend to flow more slowly at low temperatures than oils with lower viscosity (thinner oils). Oil viscosity is graded by measuring the time it takes for a standard amount of oil to flow through a test device – the longer it takes to flow, the higher the viscosity.
Viscosity matters because engine oils need to be able to flow smoothly into tight areas while also maintaining a thick enough coating to properly lubricate engine components. Oil that is too thin will fail to adequately coat and protect metal surfaces, while oil that is too thick may not properly flow to all the necessary areas in cold weather conditions. The right oil viscosity for your vehicle provides an optimal balance of protection and flowability.
Understanding Oil Weight Numbers and Viscosity Ratings
You’ll notice a series of numbers on every container of engine oil which indicates the oil weight and viscosity. These numbers refer to the Society of Automotive Engineers (SAE) viscosity grading system for motor oils. The scale starts at 0 and goes up to 60 – the lower the number, the thinner the oil. The higher the number, the thicker it is.
Some oils are labeled with single viscosity numbers like 10W or 20. Others have two numbers like 10W-30 or 20W-50. Here is what the different viscosity ratings mean:
- 0W, 5W, 10W, 15W, 20W, 25W: The “W” refers to “winter” or cold weather viscosity. The lower the number, the better the oil flows in cold temperatures. 0W flows easiest at very low temps.
- 20, 30, 40, 50, 60: No “W” means the oil weight rating refers to high temperature viscosity. Higher numbers mean thicker oil consistency at engine operating temperatures.
- 10W-30, 20W-50: Oils with two numbers are “multi-viscosity” and provide viscosity coverage across varying temperature ranges. For example, 10W-30 flows well in cold weather from the 10W rating, but thickens up at higher engine temperatures from the 30 rating.
When to Use Thicker Oils in Your Vehicle
Using a thicker oil generally provides more protection and lubrication for your engine components. Here are some situations where a higher viscosity oil may be preferable:
- High mileage engines: Engines with more than 75,000 miles benefit from thicker oil which can better seal worn surfaces and reduce oil consumption.
- Hot climates: In hot ambient temperatures, oil becomes thinner and flows more easily. A higher viscosity oil will maintain adequate thickness and protection in heat.
- Turbocharged engines: Turbochargers generate significant heat so thicker oils are recommended. Thinner oils may break down too quickly.
- Frequent towing or hauling: Heavy loads put more stress on the engine and oil. Thicker oils hold up better under high stress operation.
- Older engine designs: Older engines typically have looser tolerances so thicker oil does a better job of sealing clearances.
- Racing applications: Performance engines run hotter and harder, needing more robust oil to maintain protection.
Always follow your vehicle manufacturer’s recommended oil viscosity grade which takes into account the engine design and expected operating conditions. Going to a substantially thicker oil may cause issues like oil pump straining or failure to properly flow.
When Thinner, Lower Viscosity Oils Are Appropriate
While thicker oil has benefits in many situations, thinner oils have purposes too:
- Extreme cold climates: Thinner oils like 0W, 5W and 10W flow much more easily in frigid temperatures, providing faster lubrication at startup.
- High-efficiency engines: Modern engine designs have tighter tolerances and benefit from thinner oils that flow with less resistance. This improves efficiency.
- Short trip driving: Frequent short trips don’t allow the oil to fully warm up. Thinner oils flow better from a cold start.
- Very hot regions: In extreme heat, a lower viscosity oil may hold up better than an overly thick oil which becomes too viscous.
- Racing applications: Some high revving race engines are fine tuned for thinner oils to reduce parasitic drag.
The best practice is to use the manufacturer’s recommended viscosity grade for your specific vehicle and driving conditions. Striking the right balance between cold flowability and high temperature thickness is key.
Signs You May Need a Thicker or Thinner Oil
How do you know if it’s time to switch to a different viscosity oil? Here are signs your engine may benefit from thicker or thinner oil:
Consider thicker oil if:
- Oil seems to be getting consumed rapidly between changes
- You see signs of oil leaks around gaskets and seals
- Engine sounds noisier, especially on cold starts
- Oil pressure gauge reads lower than usual
Consider thinner oil if:
- Your engine sounds strained or noisy when started in very cold weather
- Fuel economy seems lower than expected
- Performance feels sluggish especially from a cold start
- Engine temperature gauge runs higher than normal
Routine oil analysis is recommended to look for signs of improper oil viscosity, especially if you notice any of the above symptoms after an oil change. Your mechanic can perform an oil change with a different viscosity to see if it resolves any issues.
Key Takeaways on Oil Viscosity and Engine Protection
- Oil thickness or viscosity is graded by weight numbers that indicate flow characteristics in cold and hot conditions.
- Higher viscosity oils generally provide more protection by maintaining a thicker oil film, but may not flow as well in cold temperatures.
- Lower viscosity oils flow better especially in cold weather, but may lack thickness for adequate protection in hot conditions.
- Multi-viscosity oils provide viscosity coverage across a range of temperatures.
- Always use the oil viscosity recommended for your specific vehicle and operating climate.
- If you notice possible signs of improper oil viscosity, have your oil analyzed and consider switching grades.
Frequently Asked Questions
What oil viscosity is best for most cars?
For most modern passenger vehicles driven in moderate climates, a multi-viscosity oil with a 5W or 10W winter rating and a viscosity around 30 at high temperatures (like 5W-30 or 10W-30) offers versatile protection.
Should I use thicker oil as my car gets older?
Using slightly thicker oil as an engine accumulates miles is a good way to provide additional protection against wear, provided you stay within the recommended viscosity range.
Is it bad to use oil that is too thick?
Oil that is substantially thicker than recommended can cause issues like oil starvation at startup, strain on the oil pump, and reduced fuel economy. Follow your owner’s manual for proper viscosity.
Will thinner oil damage my engine?
As long as it meets the recommended viscosity grade, thinner oil will not directly damage your engine. However, oil that is too thin may lead to accelerated wear over time.
Can I switch oil viscosities with every oil change?
It’s generally fine to vary your oil viscosity within the recommended range if you want thicker protection in winter or thinner flow in summer. Don’t make dramatic viscosity swings.
How often should oil viscosity be checked?
Oil viscosity is one parameter that should be analyzed whenever you have a used oil analysis done. For most drivers this may mean every 1-2 years to spot trends.
Conclusion
Engine oil viscosity is a compromise between optimum cold weather flow and adequate high-temperature engine protection. The right oil provides the best of both worlds across a range of operating conditions. Heavier viscosity oils typically offer increased protection, but lighter viscosity oils provide easier cold weather starting and fuel economy benefits. Always consult your owner’s manual and consider your own driving environment when choosing the appropriate oil thickness. With the right viscosity matched to your engine and climate, you can maximize engine longevity and performance.
