Short answer
JASO M345 is the Japanese standard for oils used in two-stroke gasoline engines such as motorcycles, chainsaws and other air-cooled equipment. It defines three current grades, FB, FC and FD, based on lubricity, initial torque, detergency, exhaust smoke and exhaust system blocking. FD is the highest grade; the original FA grade was dropped in 2004.
What the five test areas measure
Two-stroke oil is burned with the fuel, so the standard looks at more than wear protection. Lubricity measures how well the oil prevents scuffing between the piston and cylinder. Initial torque looks at friction when a test engine is started up on the oil. Detergency rates how clean the piston and rings stay. Exhaust smoke measures visible smoke from burning the oil, and exhaust system blocking looks at deposits that build up in the exhaust.
Each result is expressed as an index compared against a JASO reference oil, and a grade is awarded only when every index clears that grade’s minimum.
How FB, FC and FD differ
FB was a step up from the original FA minimum in lubricity, detergency, smoke and exhaust blocking. FC keeps FB’s lubricity and initial torque requirements but is much stricter on detergency, smoke and exhaust blocking, which is why FC is often described as a low-smoke grade.
FD matches FC on most requirements and adds a considerably higher detergency requirement, aimed at keeping pistons and rings clean at high temperature. In the 2004 revision JASO dropped FA and introduced FD as the top grade.
Where JASO M345 grades are used
Equipment makers for motorcycles, scooters, snowmobiles, chainsaws, trimmers and blowers commonly list a JASO M345 grade, often FC or FD, sometimes together with the ISO-L-EGC or ISO-L-EGD grades that ISO built on the same test methods. The mixing ratio, such as 50:1, comes from the equipment maker and is separate from the oil grade.
Water-cooled outboard motors are a different case. Outboard makers generally specify NMMA TC-W3 for two-stroke outboards, so do not assume a JASO grade covers an outboard unless the manual says so.
Registration and labels
Like JASO’s four-stroke motorcycle standard, M345 works through registration: registered oils appear on JASO’s published list and carry the JASO mark with the grade. A bottle that only says it is “suitable for” an FC or FD application is a marketer’s claim. Check the grade and any equipment-maker approval in the manual before mixing a tank.
Frequently asked questions
Is JASO FD better than FC?
FD has a higher detergency requirement than FC and matches it on most other tests. If your equipment calls for FC, an FD oil meets a stricter detergency level, but follow any maker-specific requirement in the manual.
Does JASO FD tell me the mix ratio?
No. The grade describes oil performance. The fuel-to-oil ratio comes from the engine maker and may differ from what an oil label suggests.
Can I use JASO FD oil in a two-stroke outboard?
Outboard makers typically call for NMMA TC-W3. Use the oil category in the outboard’s manual.
General maintenance information. Always follow your vehicle or equipment manufacturer’s requirements and the current product data. Questions? Email [email protected].