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.

AMSOIL Diesel Motor Oils

AMSOIL Signature Series Max-Duty Synthetic Diesel Oil 15W-40
Signature Series Max-Duty Synthetic Diesel Oil 15W-40
AMSOIL Signature Series Max-Duty Synthetic Diesel Oil 5W-40
Signature Series Max-Duty Synthetic Diesel Oil 5W-40
AMSOIL Signature Series Max-Duty Synthetic Diesel Oil 0W-40
Signature Series Max-Duty Synthetic Diesel Oil 0W-40
AMSOIL Signature Series Max-Duty Synthetic Diesel Oil 5W-30
Signature Series Max-Duty Synthetic Diesel Oil 5W-30
AMSOIL Heavy-Duty Synthetic Diesel Oil 15W-40
Heavy-Duty Synthetic Diesel Oil 15W-40
AMSOIL Heavy-Duty Synthetic Diesel Oil 5W-40
Heavy-Duty Synthetic Diesel Oil 5W-40
AMSOIL Heavy-Duty Synthetic Diesel Oil 10W-30
Heavy-Duty Synthetic Diesel Oil 10W-30
AMSOIL DOMINATOR 20W-50 Competition Diesel Oil
DOMINATOR 20W-50 Competition Diesel Oil
AMSOIL SAE 15W-40 Heavy-Duty Diesel and Marine Oil
SAE 15W-40 Heavy-Duty Diesel and Marine Oil
AMSOIL Series 3000 5W-30 Synthetic Heavy Duty Diesel Oil
Series 3000 5W-30 Synthetic Heavy Duty Diesel Oil
AMSOIL 10W-30/SAE 30 Synthetic Heavy-Duty Diesel Oil
10W-30/SAE 30 Synthetic Heavy-Duty Diesel Oil
AMSOIL Premium Protection 20W-50 Synthetic Motor Oil
Premium Protection 20W-50 Synthetic Motor Oil
AMSOIL Premium Protection 10W-40 Synthetic Motor Oil
Premium Protection 10W-40 Synthetic Motor Oil
Become a Preffered Customer Today!
Add a six-month or one-year Preferred Customer membership to your cart and save up to 25 percent on today’s order.
Can diesel oils be used in gasoline engines?
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?
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.
Does AMSOIL offer diesel oils for equipment calling for the API CK-4 specification?
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?
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.
Accounts
AMSOIL Retail Account
AMSOIL Retail Account
AMSOIL Preferred Customer
AMSOIL Preferred Customer
AMSOIL Dealer Account
AMSOIL Dealer Account
AMSOIL Commercial Account
AMSOIL Commercial Account
Save up to 25% on Amsoil Products
 
AUTHORIZED AMSOIL DEALER