Choosing the right diesel engine oil can be confusing. With various classifications like API CK-4, FA-4, and others like CJ-4 or SP oil, it’s important to understand what these standards mean and how they affect your truck or heavy-duty vehicle.
Let’s break down the differences between CK-4 and FA-4, what types of diesel oil are best, and how often you should change your oil
What Is API CK-4 Oil?
API CK-4 is a diesel engine oil classification introduced by the American Petroleum Institute (API) in 2016 to replace the older CJ-4 standard. It’s designed for high-performance, heavy-duty engines, including those with turbochargers and exhaust after-treatment systems.
Key Benefits of API CK-4:
Improved oxidation control
Better protection against engine wear
Compatible with older diesel engines
Maintains engine cleanliness under tough conditions
Many fleets and pickup trucks like Ford Super Duty diesel models use CK-4 oils for daily operation.
What Is API FA-4 Oil?
API FA-4 oil was also introduced in 2016 but is designed for newer diesel engines built for maximum fuel efficiency. FA-4 uses a lower high-temperature viscosity (typically 10W-30), which reduces engine drag and improves fuel economy.
But There’s a Catch:
FA-4 is not backward-compatible. You should only use FA-4 if your engine specifically recommends it.
CK-4 vs FA-4: Which One Should You Use?
| Feature | CK-4 | FA-4 |
|---|---|---|
| Backward compatibility | ✅ Yes | ❌ No |
| Designed for older engines | ✅ | ❌ |
| Fuel efficiency | Good | Excellent |
| Engine protection | Excellent | Excellent |
| Viscosity | Standard | Lower HTHS |
Verdict:
If you drive a heavy-duty diesel like a Ford F250, CK-4 is likely the better option—unless your vehicle’s manufacturer specifically calls for FA-4.
What About API SP Oil?
You may come across oils labeled as API SP or see comparisons like API SP vs SN. These ratings are for gasoline engines, not diesel. While SP oil has improvements for turbocharged gasoline vehicles, it’s not appropriate for diesel engines unless the label includes dual ratings like “SP/CK-4.”
So if you’re buying motor oil for diesel engines, make sure the product says API CK-4, FA-4, or both.
Best Diesel Engine Oils: What to Look For
Choosing the best diesel engine oil depends on:
Engine type (turbo or non-turbo)
Viscosity recommended by the manufacturer
Operating conditions (e.g., towing, long hauls, city driving)
Look for oils labeled:
Best synthetic diesel oil
Heavy duty diesel motor oil
Top diesel oil
Diesel truck oil
Synthetic oils offer better protection and longer life, especially in extreme weather.
How Often Should You Change Diesel Engine Oil?
The diesel oil change frequency depends on:
Type of oil used (conventional vs synthetic)
Engine size and design
Driving habits
Most diesel trucks like the Ford F250 Super Duty require oil changes every 7,500–15,000 miles, depending on conditions. Be sure to follow your owner’s manual for the recommended diesel engine oil change interval.
Why It Matters:
Failing to change oil on time can reduce engine lifespan, hurt fuel economy, and cause costly repairs—especially in turbo diesel engines.
What Type of Oil Do Diesel Engines Use?
Diesel engines typically use oil that is:
Higher in detergents to clean soot and deposits
Thicker in viscosity (e.g., 15W-40 or 5W-40)
Rated for extreme loads and temperatures
Some common labels include:
Synthetic diesel motor oil
Engine oil for diesel trucks
Good quality diesel engine oil
Do Diesel Engines Need Special Oil?
Yes. Diesel engines operate at higher compression ratios and often handle greater loads than gasoline engines. That’s why motor oil for diesel contains different additives.
If you’re running a turbo diesel, using the best oil for turbo diesel engines ensures your turbo stays clean and lubricated, reducing the risk of failure.
CK-4 vs CJ-4: Is There a Difference?
Yes. CK-4 replaced CJ-4 to offer:
Better shear stability
Improved oxidation control
Enhanced aeration performance
If you were previously using CJ-4, you can safely switch to CK-4 for improved protection.
How Often Do Diesel Cars Need Oil Changes?
For diesel cars, not just trucks, diesel car oil change intervals tend to be longer than gas engines. While gasoline engines may need an oil change every 5,000 miles, diesel car oil change frequency often ranges from 7,000 to 10,000+ miles.
What Oil Do Diesel Engines Use?
The short answer: check your manual. But in general:
For pickup trucks: use heavy-duty synthetic or blend diesel oil
For fleet trucks: follow OEM specs, often recommending FA-4 or CK-4
For older diesel engines: avoid FA-4 unless the manual permits it
Conclusion
Choosing between API CK-4 vs FA-4 comes down to what your engine needs. Both are excellent oils—but serve different purposes. CK-4 is versatile and widely compatible, while FA-4 is cutting-edge but limited to newer engines.
When in doubt, stick to recommended diesel engine oil from your manufacturer. Whether you drive a Ford F250, a turbocharged pickup, or manage a fleet of diesel trucks, the right engine oil for diesel engines is key to performance, longevity, and fuel efficiency.