Okay to add Sea Foam to a full tank of gas? [SOLVED] Asked by Johnson Q. In Virginia Is it okay to add Sea Foam Motor Treatment when the gas tank is already full on a 1999 Toyota 4Runner?
You can add Sea Foam Motor Treatment to your gas tank at any time – it’s completely fine to add when the tank is near full.
That said, one of the best ways to get the most cleaning power out of a can of Sea Foam is to add a full can to a low tank of fuel (1/8 tank or so). Then, drive until almost empty before refueling (at least 20 miles if you can to give the Sea Foam time to run through the fuel system). This creates a high cleaning concentration that works much faster and better than adding to a high amount of fuel.
High Mileage Motor Treatment works very well for this, too.
Hope that helps and thanks for using it!