Every Suzuki 4-stroke outboard in our manuals runs on regular unleaded with a minimum pump octane of 87 ((R+M)/2 method), with three exceptions: the DF250AP/300AP call for 89 minimum, and the DF350A manual recommends premium but accepts 89 as the minimum, while the DF300B stays at 87. Ethanol blends are allowed up to 10% ethanol on every model. Suzuki says to use alcohol-free gasoline whenever possible, never leaded fuel, and never stale fuel.
The table below gives the figures exactly as each owner's manual prints them, with the year of the manual, because the older manuals also set limits for MTBE and methanol that the newer ones dropped. The service manuals add a Research-method octane figure and a single-additive limit; those are in the last column.
Fuel requirements by model
| Family (owner's manual year) | Minimum octane, as printed | Ethanol | MTBE / methanol (owner's manual) | Service manual adds |
|---|---|---|---|---|
| DF2.5 (2019) | 87 pump octane ((R+M)/2) | Not greater than 10% | Not stated | 87 (R/2 + M/2) or 91 (Research); single additive max 5% methanol, 10% ethanol, 15% MTBE |
| DF4A/DF6A (2019) | 87 pump octane ((R+M)/2) | Not greater than 10% | Not stated | DF4/5/6 service manual: 87 ((R+M)/2) or 91 (Research); 5% methanol, 10% ethanol, 15% MTBE |
| DF8A/DF9.9A (2014) | 87 pump octane ((R+M)/2) | Not greater than 10% | MTBE not greater than 15%; do not use fuel with more than 5% methanol | 87 (R+M/2) or 91 (Research); 5% methanol, 10% ethanol, 15% MTBE |
| DF9.9B/DF15A/DF20A (2014) | 87 pump octane ((R+M)/2) | Not greater than 10% | MTBE not greater than 15%; do not use fuel with more than 5% methanol | 87 (R/2 + M/2) or 91 (Research); 5% methanol, 10% ethanol, 15% MTBE |
| DF9.9B/DF15A/DF20A (2020) | 87 pump octane ((R+M)/2) | Not greater than 10% | Not stated (the MTBE and methanol limits were dropped from this edition) | Same service manual as above |
| DF25A/DF30A (2018) | 87 pump octane ((R+M)/2) | Not greater than 10% | Not stated | 87 (R/2+M/2) or 91 (Research); 5% methanol, 10% ethanol, 15% MTBE |
| DF40A/DF50A/DF60A (2022) | 87 pump octane ((R+M)/2) | Not greater than 10% | Not stated | DF60A service manual: 5% methanol, 10% ethanol, 15% MTBE |
| DF75/DF90A (2023) | 87 pump octane ((R+M)/2) | Not greater than 10% | Not stated | DF70A–DF100B service manual: 87 (R/2+M/2) or 91 (Research); 10% ethanol |
| DF100A/DF115A/DF140A (2016) | 87 pump octane ((R+M)/2) | Not greater than 10% | MTBE not greater than 15%; do not use fuel with more than 5% methanol | 87 (R/2+M/2) or 91 (Research); 5% methanol, 10% ethanol, 15% MTBE |
| DF115B/DF140B (2023) and DF115BG/DF140BG (2022–2023) | 87 pump octane ((R+M)/2) | Not greater than 10% | Not stated (no MTBE or methanol wording in the DF115BG/140BG edition) | Not in our files |
| DF150A/DF175A/DF200A (2020 and 2023) | 87 pump octane ((R+M)/2) | Not greater than 10% | Not stated (no MTBE or methanol wording in the 2023 edition) | Not in our files |
| DF150AP/DF175AP/DF200AP (2020) | 87 pump octane ((R+M)/2) | Not greater than 10% | Not stated | Not in our files |
| DF225/DF250 (2021) | 87 pump octane ((R+M)/2) | Not greater than 10% | Not stated | Not in our files |
| DF250AP/DF300AP (2021) | 89 pump octane ((R+M)/2) | Not greater than 10% | Not stated | Not in our files |
| DF300B (2023) | 87 pump octane ((R+M)/2); any oxygenated blend must be at least 87 | Not greater than 10% | Not stated (no MTBE or methanol wording in this edition) | Not in our files |
| DF350A (2023) | Premium recommended, not required; minimum 89 pump octane ((R+M)/2) acceptable; any oxygenated blend must be at least 89 | Not greater than 10% | Not stated (no MTBE or methanol wording in this edition) | Not in our files |
The emission-control label reproduced in most of these manuals says the same thing in one line: this engine is certified to operate on unleaded gasoline of 87 octane ((R+M)/2 method) or greater, or 89 octane on the DF250AP/300AP and the DF350A.
Reading the octane numbers
The (R+M)/2 figure is the number posted on US pumps, so 87 means regular. The service manuals print a second figure, "91 (Research method)". That is the same fuel rated by the Research method (RON), which is the number used on pumps in most countries outside North America. It is not a call for premium. Suzuki's service manuals put it this way: alcohol-free unleaded gasoline with a minimum pump octane rating of 87 (R/2 + M/2 method) or 91 (Research method), and blends of unleaded gasoline and alcohol with equivalent octane content may be used.
Suzuki does not ask for higher octane on any motor below the DF250AP. The DF2.5 manual has one practical note: if engine pinging is experienced, substitute another brand, as there are differences between brands.
Ethanol: E10 is the limit
Every manual uses the same wording: blends of unleaded gasoline and ethanol (grain alcohol), also known as gasohol, may be used if the ethanol content is not greater than 10%. E10 is inside that limit. E15 is 15% ethanol and E85 is far beyond it; neither is within what any of these manuals allow, and the manuals do not describe any Suzuki outboard as approved for them. Suzuki also asks that any oxygenated fuel blend you use has an octane rating of at least 87 pump octane ((R+M)/2 method), or 89 on the DF350A.
Two more things the manuals say about alcohol fuels. First, fuels containing alcohol can cause paint damage, which is not covered under the New Outboard Motor Limited Warranty, so wipe up spills. Second, methanol (wood alcohol) is treated separately from ethanol: the manuals that mention it say to avoid methanol blends whenever possible and DO NOT USE fuels containing more than 5% methanol under any circumstances. Fuel with 5% or less methanol may be suitable only if it contains cosolvents and corrosion inhibitors. The service manuals set those limits for a single additive, not a combination: 5% methanol, 10% ethanol, 15% MTBE.
Ethanol's practical problem is that it absorbs water from the air, and water in the fuel is what the low-pressure filter and the water-separating filter are there to catch. That is covered in the next two sections.
Stale fuel and stabilizer
Suzuki's manuals are direct about old fuel: gasoline kept in the fuel tank for long periods of time will produce varnish and gum, which can damage the engine. Use only unleaded gasoline; use of leaded gasoline can cause engine damage, and improper or poor quality fuel can affect performance and damage the motor and fuel system.
For storage, the procedure in every manual is the same. Fill a high quality fuel stabilizer to the fuel tank according to the instructions on the stabilizer can, then run the engine at about 1500 r/min in neutral for five minutes to distribute the stabilized fuel through the engine (the DF2.5 runs at about 2500 r/min for the same five minutes). Our storage procedure page has the full step list by family, and Suzuki fuel conditioner is the stabilizer we stock.
Water-separating fuel filter
Nearly every owner's manual from the DF9.9B up carries the same recommendation: Suzuki recommends that you install a water-separating fuel filter assembly between your boat's fuel tank(s) and outboard motor(s). The DF9.9B/15A/20A manual adds that filtration of this type helps prevent water in the boat's tank from contaminating the fuel system. The maintenance schedule then treats it like any other service item: replace the filter element every 12 months, or more frequently if recommended by the filter manufacturer.
The motor's own low-pressure fuel filter has its own interval. On the DF4A/6A, DF8A/9.9A, DF9.9B/15A/20A, DF25A/30A and DF40A–60A the manual says to inspect it at the initial 20 hours (1 month) and every 100 hours (12 months), and replace it at every 400 hours (2 years). On the DF75/90A, DF100A/115A/140A, DF115BG/140BG, DF150A/175A/200A (2023 manual) and DF300B/350A the low pressure fuel filter must be replaced by an authorized Suzuki Marine Dealer, again at every 400 hours (2 years); the DF100A/115A/140A, DF115BG/140BG, DF150A/175A/200A and DF300B/350A maintenance charts also mark it for inspection at the initial 20 hours (1 month) and every 100 hours (12 months). The DF2.5 fuel filter is inspected by a dealer at every 100 hours (12 months). If you have a fuel system with a water sensor and the lamp comes on, our water-in-fuel warning page explains what it means, and this post covers why the separator matters.
Parts for this job
We carry the Suzuki water-separating fuel filter assembly for 140 hp and below and the assembly for 150 hp and above, replacement elements for both, the low-pressure fuel filter, and the rest of the Suzuki fuel filters and separators. Boat Max Online is an authorized Suzuki, Honda and Yamaha dealer; orders over $149 ship free to the lower 48.
Sources: Suzuki owner's manuals for DF2.5, DF4A/6A, DF8A/9.9A, DF9.9B/15A/20A (2014 and 2020), DF25A/30A, DF40A/50A/60A, DF75/90A, DF100A/115A/140A (2016, 99011-90J70-03B), DF115B/140B (2023) and DF115BG/140BG (2022–2023, 99011-99L20-03B), DF150A/175A/200A (2020; 2023, 99011-96LM0-03B), DF150AP/175AP/200AP, DF225/250, DF250AP/300AP and DF300B/350A (2023, 99011-98L60-03B); Suzuki service manuals 99500-97J01-01E, 99500-91J03-01E, 99500-99J00, 99500-89L00-01E, 99500-94L10-01E, 99500-88L01-01E, 99500-87L10-01E and 99500-92J00-01E. Figures are Suzuki's published values; confirm against the manual for your model year and serial number.