Two-stroke oil: JASO FB, FC, FD and ISO EGD

A chainsaw, a strimmer, a brushcutter, an old scooter, an outboard at the holiday cottage: nearly every household has a two-stroke somewhere. And on the shop shelf, side by side, stand bottles marked “2T”, each with its own set of labels: JASO FD, ISO-L-EGD, API TC, and some of them TC-W3 as well. The shop assistant waves a hand: “Two-stroke is two-stroke, the main thing is to mix it 1:50.” Sound familiar? In fact, behind each of these labels there is a separate document, and not all of them are about your engine.

Two-stroke engines have already had a short mention in the article on JASO motorcycle oils: classes FB, FC and FD got a single paragraph there. Here we go through them in detail, together with ISO, API TC and the boating TC-W3.

Why two-stroke oil is special

A conventional two-stroke (the kind where the mixture passes through the crankcase) has no separate oil sump. The oil arrives with the petrol, lubricates the crankshaft bearings, the piston and the cylinder, and then burns and leaves through the exhaust. The oil in a four-stroke engine works like the water in a central heating system: round and round, for months. Two-stroke oil is more like the petrol itself: used once and gone for good.

Hence the requirements. The oil has to lubricate well in a single pass and then burn as cleanly as possible: no thick smoke, no deposits on the piston rings (rings sticking in their grooves is one of the classic ailments of a two-stroke) and no build-up that slowly chokes the exhaust port and the silencer. So two-stroke oil is judged not only on how it lubricates but also on how it burns.

JASO M345: what FB, FC and FD mean

JASO M345 is the Japanese standard for two-stroke petrol engine oils, developed by the Society of Automotive Engineers of Japan (JSAE). An oil is tested on four counts: lubricity, detergency, smoke and exhaust system blocking. There are three classes, FB, FC and FD, from lower to higher. There is no longer a class FA in the current editions.

The minimums under the 2018 and 2024 editions of JASO M345:

The indices are calculated relative to a reference oil. The smoke figures here follow the 2018 method; the 2024 edition of the standard introduced a new method, and the minimums under it are 40 for FB and 80 for FC and FD. That said, JALOS still accepts submissions under the old guidelines too, with different engines and different minimums (there FB and FC are tested for one hour and without a skirt rating), so the list contains oils submitted under both editions. Two more limits are the same for all three classes: viscosity at 100 °C of at least 6.5 mm²/s and a flash point of at least 70 °C. What these figures mean on a data sheet is explained in the article on the oil data sheet.

And now the interesting part. The minimum for lubricity is the same for all three classes: in the new editions it is an index of 103 (and 98 for initial torque), and in the old guidelines it is 95, again one figure for everyone. So on minimum requirements FB lubricates no worse than FD; the difference lies in smoke, deposits and how clean the engine stays. FD is the top class (JASO itself calls it an improved FC), so class-wise it is fine in an engine that only needs FB. The reverse does not hold: if the manual says FD, do not pour FB into it.

It is telling that in the new editions lubricity and cleanliness are tested on a blower engine rather than a motorcycle one, as before, while smoke and exhaust blocking are still tested on a generator engine, only a different model. The reason is simple: the previous test engine went out of production, and demand, as the JASO committee itself puts it, rests mainly on small, light engines for power equipment.

The JASO frame: submitted, not approved

JASO does not approve oil. The supplier orders the tests itself and submits the documents, and the JASO committee (documents are received on its behalf by the Japan Lubricating Oil Society, JALOS) checks that everything is filled in and that the figures fit the class, then adds the oil to the list. The quality and the class are guaranteed by the supplier on its own responsibility: the JASO guidelines on applying the standard say so outright, and it is exactly what the supplier has to put on the label. The same guidelines forbid advertising an oil as “JASO approved”. All the committee can do is spot-check oils from the market and compare them with the submitted documents.

Anyone can check the code, though. On a can with the JASO frame, next to the class there is a nine-character oil code: three digits for the telephone country code of the oil’s supplier or manufacturer (081 is Japan), three Latin letters for the supplier code and three digits for the supplier’s own number. The JASO committee publishes the list of submitted oils on its JASO two-stroke oils page (the list itself is a separate PDF): it holds about six hundred oils, and more than half of them are FC. Check the code first, then the class: a name in the English list may differ slightly from the one on the can. If the code is not in the list, or the class is different, be wary of that bottle (how else to tell a genuine requirement from a manufacturer’s claim is covered in the article on how to check an oil approval).

ISO-L-EGB, EGC, EGD: similar, but not the same

The international standard ISO 13738 (the current edition dates from 2011) describes oils for crankcase-scavenged two-stroke petrol engines (motorcycles, snowmobiles, chainsaws) and the classes EGB, EGC and EGD, set out in the ISO 6743-15 classification. The “L” in ISO-L-EGD is simply the designation of the “lubricants” class.

The ISO classes are built on the Japanese ones, but with an addition: ISO added a piston skirt cleanliness rating, which the old FB and FC did not have, and for the two higher classes a longer, three-hour detergency test as well. The Japanese standard later caught up: first in 2002 for FD, and in the 2018 and 2024 editions all three classes are rated after 180 minutes of running, skirt included. But the JASO test engine is now different too, and so are the minimum indices, whereas ISO 13738 has not been changed since 2011. So the pairs FB-EGB, FC-EGC and FD-EGD are close in purpose, but an equals sign between them is only a common shorthand.

Two more things matter to the buyer. First, ISO does not certify oils and keeps no register, so ISO-L-EGD on a can is the oil maker’s word, and there is nowhere at ISO to check it. Second, the pairings on cans are sometimes untypical: in our catalogue you find FC next to EGD and FB next to EGC. So look for the label the engine maker named: if it says FD, look for FD; if it says EGD, look for EGD.

API TC and TC-W3: quite different paths

API TC is an old American class, and it appears on almost every two-stroke oil in our catalogue (26 of 29). The specification ASTM D4859, which described oils of this class (for two-strokes, “typically other than outboard motors”, prone to ring sticking and piston scuffing), was withdrawn by ASTM in 2022 without a replacement. On its own, TC on a bottle says little; look at the JASO or ISO class beside it.

TC-W3 is a completely different story: it is a testing and certification programme of the American National Marine Manufacturers Association (NMMA) for water-cooled two-stroke outboard engines. The oil receives a licence and a registration number, “RL”, and NMMA publishes the list of registered TC-W3 oils on its website. The “W” stands for water-cooled. If an outboard maker calls for TC-W3, look for TC-W3 with an RL number. But for an air-cooled chainsaw or scooter TC-W3 guarantees nothing: it is no substitute for the JASO or ISO class that the manual calls for.

Premix or a separate tank?

Two-stroke oil is either mixed with petrol in a can (premix) or poured into a separate tank, from which a pump delivers it (as in many scooters and motorcycles). The data sheets of many two-stroke oils say that they are already “pre-diluted” and so suit both mixing and separate lubrication. And the same sheets say that the oil must be dosed as the engine maker recommends. But there are also premix-only oils: for an engine with a separate tank, the data sheet must state outright that the oil is suitable for separate lubrication.

The ratio is a requirement of the engine maker, just like the oil class. Husqvarna, for instance, gives 50:1 for its chainsaws, that is 2% oil (100 ml to 5 litres of petrol), refers you to the manual for the details of a specific model and advises mixing about a month’s supply at most. Car engine oil has no JASO FB, FC or FD class, so it does not meet the manual’s requirements for a two-stroke even if it is “left over from an oil change”.

Synthetic or mineral?

The JASO or ISO class is set by the tests, not by the word “synthetic” on the label. In our catalogue the FB oils whose base is stated are mineral, while FD oils turn up both synthetic and semi-synthetic. An FD oil on a semi-synthetic base is still FD, and “synthetic” without a class is just a word on a can. Synthetic is better than mineral in its working properties, but will the engine of your strimmer, which the manual says needs FB, feel the difference? More in the article on whether synthetic or mineral is better.

What does this mean for the owner of a two-stroke?

1. The manual. Find the class (JASO FB, FC, FD or ISO-L-EGB, EGC, EGD), the ratio and the method of lubrication: premix or a separate tank. For an outboard it will usually say TC-W3.

2. The can. The right class, and next to it the nine-character JASO code. The code is easy to check against the JASO list; for TC-W3, the RL number in the NMMA list.

3. The ratio. Measure it, do not pour by eye, and do not mix a whole season’s supply in advance.

I will say it again: the engine maker decides which oil to use, and for a chainsaw that rule applies just as it does for a car (how to find out the manufacturer’s recommendations is covered separately). And “two-stroke is two-stroke” is not an oil class, it is a shop assistant’s saying.