hard to say

depend when I feel I need. Like I plan change spark plugs then I do.

mostly 5,000 to 50,000 miles then do sea foam. But sea foam is $8 so I do every 20,000 miles until mpg drop no reason then I use sea foam.

for engine in crankcase I don't use sea foam I use automatic transmission oil then pour 1 qts then put 500 miles on it then change oil. To get all sludge out.

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