Vintage Outboard Motor Mix Ratios by Brand and Year
Most outboards built before the mid-1960s call for 16:1 to 24:1. Most from the 1970s onward call for 50:1.
The decal on the motor cover or the owner's manual is the final word, because ratios changed from model to model and year to year. Use a modern NMMA TC-W3 outboard oil at the ratio specified. Don't go leaner than spec on an old motor.
Vintage outboard mix ratio chart
Typical original recommendations. Individual models differ, so treat this as a starting point and confirm with the decal, manual or a model-specific forum.
| Brand | Era | Usual premix ratio | Calculator |
|---|---|---|---|
| Johnson / Evinrude (OMC) | 1940s to early 1960s | 16:1 to 24:1 | Mix at 24:1 |
| Johnson / Evinrude (OMC) | mid-1960s to 1980s | 50:1 (with TC-W rated oil) | Mix at 50:1 |
| Johnson / Evinrude (OMC) | 1984 to 2000s with VRO / oil injection | No premix (oil injected); 50:1 if injection is removed | Mix at 50:1 |
| Mercury / Mariner | 1950s to 1960s | 20:1 to 24:1 | Mix at 24:1 |
| Mercury / Mariner | 1970s onward | 50:1 | Mix at 50:1 |
| Yamaha | 1980s to 2000s premix models | 100:1 with Yamalube 2-M (50:1 during break-in or with other oils) | Mix at 50:1 |
| Suzuki / Tohatsu / Nissan | 1970s to 2000s | 50:1 (often 25:1 for break-in) | Mix at 50:1 |
| Chrysler / Force | 1960s to 1990s | 50:1 for most later models; early models richer | Mix at 50:1 |
| British Seagull | 1930s to 1970s | 10:1 on most models; 25:1 on later motors marked for it | Mix at 10:1 |
| Scott-Atwater, Elgin, Sea King, Martin, Champion | 1930s to 1950s | 16:1 typical (some 12:1 to 24:1) | Mix at 16:1 |
Check for oil injection before you premix. Many 1980s and later outboards (OMC VRO, Mercury Optimax and injected models, Yamaha Precision Blend) have an oil tank and pump. They take straight gas. Premixing on top of working injection doubles the oil; removing injection means you must premix every tank.
How much oil for a vintage outboard tank
The classic portable outboard tank holds 6 US gallons (about 22.7 litres). Here is how much oil each vintage ratio needs:
| Ratio | Per US gallon | Per 6-gallon tank | Per litre |
|---|---|---|---|
| 10:1 | 12.8 fl oz | 76.8 fl oz | 100 mL |
| 16:1 | 8 fl oz | 48.0 fl oz | 62.5 mL |
| 20:1 | 6.4 fl oz | 38.4 fl oz | 50 mL |
| 24:1 | 5.3 fl oz | 32.0 fl oz | 41.7 mL |
| 25:1 | 5.1 fl oz | 30.7 fl oz | 40 mL |
| 32:1 | 4 fl oz | 24.0 fl oz | 31.3 mL |
| 40:1 | 3.2 fl oz | 19.2 fl oz | 25 mL |
| 50:1 | 2.6 fl oz | 15.4 fl oz | 20 mL |
For other amounts use the mix calculator or see how much oil for 6 gallons.
24:1 or 50:1? Running old outboards on modern oil
Old ratios like 16:1 and 24:1 were written for the non-detergent SAE 30 or 40 motor oils of the time. Modern TC-W3 oils protect much better, which is why manufacturers moved to 50:1 in the mid-1960s and later. That raises the common question: can a 24:1 motor run 50:1 today?
- Some manufacturers did approve it. OMC, for example, later approved 50:1 with its own certified oil for many motors originally rated 24:1, but not every model.
- Old motors are worn. Needle bearings, crank seals and rings on a 60-year-old motor have less margin than when new.
- The common, safe middle ground among restorers is to run the original spec, or 32:1 at most, with a quality TC-W3 oil. More oil means a bit more smoke and plug fouling; too little oil means a scored piston.
- Never use plain motor oil (car engine oil) in a 2-stroke. Use oil made for 2-strokes, rated TC-W3 for water-cooled outboards.
For full charts of these rich mixes, see the 25:1 and 16:1 pages.
Finding your outboard's correct ratio
- Look for the decal on the engine cover or near the fuel connector. Many older motors print the ratio there.
- Find the model number on the plate on the transom bracket or swivel bracket, then look up the owner's or service manual for that model and year.
- Check the tank cap. Some original fuel tanks have the ratio molded on the cap.
- Ask a brand-specific club or forum with the model number. Owners of vintage Johnson, Evinrude, Mercury and Seagull motors keep detailed records.
- When in doubt, run richer, not leaner. An extra-rich mix smokes; a lean one seizes.
Recommissioning an old outboard
- Drain old fuel from the tank, lines and carburetor. Fuel that sat for years becomes varnish. See fuel storage.
- Replace the water pump impeller. A cracked impeller from long storage is the main cause of overheating. See engine overheating.
- Replace fuel lines and the primer bulb; old rubber cracks in ethanol fuel.
- Check compression on all cylinders and fit fresh plugs. See how to read a spark plug.
- Mix fresh fuel at the correct ratio with a TC-W3 outboard oil, and consider ethanol-free gas.
- Run it in a test tank or on muffs and confirm a strong stream from the tell-tale before you head out.
Frequently Asked Questions
What is the fuel mix ratio for an old Johnson or Evinrude outboard?
Most Johnson and Evinrude outboards from the 1940s to early 1960s used 16:1 to 24:1. Most from the mid-1960s to the 1980s used 50:1 with TC-W rated oil. Check the decal on the motor or the manual for your model and year.
Can I run a 24:1 outboard at 50:1 with modern oil?
Some manufacturers later approved 50:1 for certain 24:1 motors when using their certified oil, but not all. Old motors are worn, so many restorers stay at the original ratio or 32:1 at most, using quality TC-W3 oil.
What oil should I use in a vintage outboard?
Use an NMMA TC-W3 rated 2-stroke outboard oil at the ratio specified for your motor. Never use automotive motor oil.
How much oil do I add to a 6-gallon tank at 24:1?
At 24:1 add 32 fluid ounces (about 946 mL) of oil to 6 US gallons of gas. At 50:1 it is 15.4 fluid ounces.
How do I know if my outboard has oil injection?
Look for a separate oil tank or reservoir under the cowling or in the boat, with a line running to the engine. Injected motors take straight gas. If you remove the injection system, you must premix every tank.