AMSOIL Diesel Oils


FAQS: Heavy Duty & Off-Road Diesel

Is it safe to use Engine and Transmission Flush in diesel engines?
Answer: Yes. AMSOIL Engine and Transmission Flush helps restore operating efficiency, increase fuel economy and reduce emissions in both gasoline and diesel engines and automatic transmissions. Its potent, detergent-based formula dissolves and disperses sludge, varnish and deposits, promoting lower operating temperatures and reduced oil consumption.
Can diesel oils be used in gasoline engines?
Answer: It depends; some AMSOIL synthetic diesel oils carry gasoline specifications. Check the product data bulletin for specific product and drain interval recommendations.
Can I switch from API CJ-4 or CI-4+ diesel oil to API CK-4 diesel oil?
Answer: Yes, CK-4 oils are backwards-compatible, meaning they can be used in older diesel engines. CK-4 oils are designed as direct replacements for prior-generation oils, including CJ-4 and CI-4+ oils.
Why are API FA-4 diesel oils not backward-compatible?
Answer: FA-4 oils feature lower viscosity grades and are designed to help next-generation diesel engines maximize fuel economy without sacrificing engine protection. These oils have limited backward-compatibility because some older engines were not designed to operate with lower viscosity grades. It's up to each engine OEM to determine if FA-4 oils can be used in its engines. Check the owner’s manual or with the OEM for specific recommendations.
Does AMSOIL offer diesel oils for equipment calling for the API CK-4 specification?
Answer: Yes. AMSOIL Signature Series Max-Duty Synthetic Diesel Oil and AMSOIL Heavy-Duty Synthetic Diesel Oil are recommended for diesel applications calling for the API CK-4 specification.
What is the difference between AMSOIL 5W-40 and 15W-40 diesel oil?
Answer: AMSOIL 5W-40 and 15W-40 diesel oils are multi-grade oils, meaning they provide good performance in high and low temperatures. AMSOIL 5W-40 and 15W-40 both behave like SAE 40 oils in high temperatures; however, the 5W-40 is thinner than the 15W-40 at start-up and at cold temperatures.
Can CI-4 rated oil be used in 2007 or newer diesel engines?
Answer: No, we do not recommend this. Model 2007 and newer diesel engines are fitted with exhaust aftertreatment systems necessary to meet current minimum emissions requirements. API CI-4 and CI-4+ oils typically contain too much sulfated ash to be compatible with these aftertreatment systems. When in doubt, check the oil specification to determine the suitability of the oil for the intended application. We recommend using an oil meeting the manufacturer-specified diesel oil specification.

What do i need to know about API CK-4 and FA-4?

What's Happening?
Driven by federal regulations that raise the bar for fuel economy while lowering emission limits, modern diesel vehicles produce more horsepower and torque than ever, run much hotter, operate under higher pressures and have the ability to burn up to 20 percent biodiesel. These advances place new demands on diesel oil, in addition to demands for increased protection from those who depend on diesel power to make a living. AMSOIL has earned the trust of diesel equipment owners and has formulated new synthetic diesel oils that meet their demands and the demands presented by the latest diesel technology.Making Sense of new Diesel Oil Specs

Advances in Diesel Technology
Beginning Dec. 1, 2016, two new American Petroleum Institute (API) diesel oil specifications take effect, replacing the current API CJ-4 specification:
  • API CK-4 (improved performance for current model-year and older engines)
  • API FA-4 (improved performance for model-year 2017 and newer engines only)Diesel Engine

Changes to diesel engine technology have resulted in:
  • New engine materials
  • More HP and torque than ever
  • Hotter-running engines
  • Higher boost pressures
  • Acceptability of using up to B20 biodiesel
  • Two Paths Going Forward

Why two new specifications?
To comply with federal mandates to increase fuel economy and reduce emissions, manufacturers are designing engines that are tougher on oil. New diesel-oil technology is needed to protect these sophisticated new engines. Compared to the diesel engine oil you’re now using, diesel oils that meet the CK-4 or FA-4 performance specifications will deliver improved protection against wear and extreme heat.

CK-4 oils offer improved protection for both current and older engines. They are backward-compatible with the API CJ-4 diesel oil you’re likely now using.

FA-4 oils, however, are different; they are not backward compatible with API CJ-4 oils. Instead, they’re designed to help increase fuel economy and reduce emissions in model-year 2017 and newer diesel engines (when called for in the owner’s manual).

How does it affect me?
Beginning Dec. 1, 2016, diesel oils that bear the API CK-4 or API FA-4 specification on their labels will start hitting store shelves. If you’re currently using an API CJ-4 diesel oil, simply begin using an API CK-4 oil of the correct viscosity.

If you own a 2017 model-year diesel, however, the manufacturer may recommend either a CK-4 or FA-4 oil it’s up to you which to use. The choice hinges on several factors, including operating conditions and the level of importance placed on fuel economy.

The new CK-4 and FA-4 formulations allow diesel owners to reduce their maintenance costs and extend the life of their equipment, allowing them to compete profitably in markets that demand peak reliability and efficiency.

New Diesel Oils Launching Feb. 6

AMSOIL Warranty

AMSOIL guarantees the performance of its products, so you can be confident they perform as advertised. AMSOIL introduced the world’s first API-qualified synthetic motor oil and has since introduced a full line of industry firsts. For more than 40 years, AMSOIL synthetic lubricants have proven themselves in the lab, on the racetrack and on the highway.