Can I add Sea Foam Motor Treatment to old gas in a fuel tank? [SOLVED]

It depends how old the fuel is. Sea Foam Motor Treatment won’t “restore” old fuel, but it will clean gum and varnish that formed as a result of the old fuel. It’s a great way to clean a fuel system that has been sitting a while with old fuel in it.

It’s almost always best to drain as much of the old fuel as possible and then add a high concentration of Sea Foam Motor Treatment in fresh fuel.

Here’s a response to a similar question about old fuel in a motorcycle tank. You can do the same thing with any kind of small engine.

Here’s what I would do: Remove as much old fuel as you can knowing that any varnish will sit at the bottom of the tank. [Don’t worry about the varnish…Sea Foam will liquefy the varnish.] Add a can of Sea Foam to the remaining fuel followed by a gallon of fresh fuel. The reason you want most of the old fuel out is to create a greater ratio of fresh fuel with highly volatile ignition vapor. [If you can’t remove some of the old gas, add the Sea Foam and new gas.] Start and run the engine for 8 minutes to allow the Sea Foam concentration to draw through the carburetor circuits. Shut off the engine and let the motorcycle sit over night or longer (2 to 3 days is better). After the long cleaning soak, add another gallon of fresh gas and run the engine for 5 to 8 minutes to heat up. Then take the motorcycle for a short spin to create more upper engine heat and compression. Much of the Sea Foam will remain in the tank and continue to clean as you go. At that point the fuel system and fuel passageways should be very clean!

In a car or truck, drain the old fuel, add a full can or two to a couple gallons of fuel, and drive until almost empty before refueling. Do that a few times and it will do a great job cleaning.

Hope that helps!