How much Sea Foam can I put in my 5.0 Mercury boat engine? [SOLVED]

Good question, Dan.

It’s safe to add a lot of Marine PRO to your boat’s gas tank. In fact, a high concentration of Marine PRO in fuel does a great job cleaning up fuel residues and deposits that often cause performance problems like rough idle, hard starts, and loss of power.

Here’s what I’d do: Wait until you have a low tank of fuel (1-2 gallons). Then, add a full 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. After that, refill your fuel tank as normal and add 1 ounce of Marine PRO per gallon of fuel. That will prevent fuel from degrading and preserve ignition vapors.

In oil, add 1 ounce of Marine PRO per quart of oil.