How much Sea Foam should you add to a 10 gallon outboard fuel tank? [SOLVED]

Thanks for the question, Brandon! Here’s what I’d recommend:

• For routine/preventative maintenance or storage: add 1 ounce of Sea Foam (or Sea Foam Marine PRO) per gallon of fuel in the tank.
• For occasional cleaning (once or twice a year): adding a high concentration of Sea Foam to your fuel will work the best to clean and overcome fuel-related performance issues. Here’s what I’d do: Wait until you have a low tank of fuel (1-2 gallons). Add a full 20 oz can of Marine PRO to the fuel. Run your boat at least 20 minutes if you can (just don’t run out of gas!), and don’t be afraid to run it hard. Then, refill your fuel tank as normal.

Here’s a (rather lengthy) explanation of why a high concentration works best. For upper engine cleaning (fuel injectors/carburetor circuits & chamber deposits that can affect running performance), it works much better to add the full can to a low amount of fuel for two reasons, 1) the cleaning concentration is considerably greater and, 2) the cleaning effect will start much faster with greater effectiveness. If you were to add Marine PRO to a high volume of tank fuel, it might take several hours of engine running for a lower concentration of the treatment to work its way through the fuel lines and through the engine. Understanding the concentration approach will go a long way in terms of understanding how Sea Foam’s engine products work for overcoming fuel residue restrictions or a rough-running engine. Pay attention to starting, smooth idle, throttle response, hole shot, acceleration, and top speed. The #1 cause of each of these issues is heavier suspended fuel gum and petroleum varnish that restricts fuel passageways. The most important thing Marine PRO does is liquefy and clear away sticky gum and varnish restrictions so the engine can go back to starting fast and running strong.

Hope that helps!