This is from the Seafoam website:
Sea Foam is a blend of highly refined additive oils and is compatible with all motor oils including synthetics. It is safe for all internal engine components and will not affect any seals, gaskets or o-rings. Sea Foam cleans oil deposits and varnish in your crankcase by safely/slowly re liquefying the old oil residue so contaminants may flow and be filtered. The longer Sea Foam is in your oil the cleaner your crankcase will become. When adding Sea Foam to clean oil, for long term maintenance cleaning, you must check your oil periodically for color and clarity, when your oil looks dirty change it. Because you added cleaning oil (Sea Foam) to your oil you may have to change oil before the expected service interval.
When adding Sea Foam to dirty oil before an oil change, for best results use 1 ½ ounces per quart of oil at least 100 miles before oil is changed.