Great question, Dannie. Yes, the best case scenario is to drain as much of the old fuel as you can, and then add Sea Foam to fresh fuel and drive it for a while.

Here’s a snippet with instructions from an article about vehicles that haven’t been run in a while:

“Gummy varnish and deposits are a common cause of problems like rough idle, loss of power, or poor fuel efficiency in a car that’s been sitting. Adding a high concentration of Sea Foam Motor Treatment or Sea Foam High Mileage to the fuel tank is an easy way to clean fuel residues and deposits from the entire fuel system. If your engine has been sitting for a long time, here are three steps to get it cleaned up and running well again with Sea Foam:

• Start by draining or syphoning the old fuel from the tank.
• Add 2-3 gallons of fresh fuel and a can of Sea Foam High Mileage to the fuel tank. If you can’t drain all the fuel, you’ll still want to add some fresh fuel to bring back fuel volatility.
• Drive until almost empty (at least twenty miles if possible) before refueling with fresh fuel.”

The Sea Foam will help clean up any gum or varnish that formed while sitting.

Good question. Yes, it’s safe to add a high concentration of Sea Foam to fuel. It’s made with 100% safe petroleum cleaning and lubricating ingredients and it’s okay to add multiple cans. In fact, adding a high concentration works much faster and better to clean than a low concentration.

However, I’d wait until the gas tank is low (1/4 -1/8 tank). Add the whole 16 oz can, and then drive for at least 10-20 miles before refueling. It’s safe to add a high concentration like that and it works very well for cleaning fuel residues and deposits.

You could add a second can at the same time (in a low tank 2-4 gallons of fuel).

Thanks for the question! Marine PRO is safe and effective in your small engines and it’s similar to Sea Foam Motor Treatment in that it cleans fuel residues and varnish and stabilizes fuel. You could use either one.

If you want a formula that’s made for tougher fuel residues and varnish, give High Mileage a try in your small engines. That’s my favorite of the Sea Foam fuel treatments and what I use in just about everything. It stabilizes fuel as well.

Good question, Gary. Yes, you can add Sea Foam to gasoline that already has Sta-Bil (or another additive/stabilizer) already in it. It’s safe and effective.

Thanks for the question! Sea Foam cleans fuel residues and varnish that form over time in any fuel system. It’ll help overcome and prevent common problems often caused by residue build up in small engines (like rough performance, hard starting, etc.). To clean residues and varnish in your small engines, add a high concentration of Sea Foam to a low tank of fuel (1:2 ratio of Sea Foam to fuel). Then, run the engine for about ten minutes, shut it off, and let it soak overnight. Start it up the next day and run it for a while.

For small engines, I like to use non-ethanol fuel, and avoid letting the fuel sit in the tank for long periods of time.

As far as ethanol goes, here’s part of an answer from another question:

“Because Sea Foam adds protective lubricity to fuel and fuel system parts, it will always help. Even though Sea Foam will help protect against ethanol and water, be careful not to buy into any false sense of security that a fuel additive is going to completely counter the harmful effects of ethanol, particularly when left in a tank for a long period of time.” (Note: in modern car and truck engines that are built to handle ethanol, there’s no need to worry about ethanol destroying fuel system parts on its own).

Here’s the full question:

https://seafoamworks.com/questions-and-answers/can-you-use-sea-foam-motor-treatment-with-ethanol-gasoline-solved/