you can add it to the crank case, gas tank or suck into your engine using the brake booster vacuum line to clean inside the heads and cylinders
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to do the cylinders,warm up the engine, take the hose off at the brake booster, stick a skinny funnel in the hose and give it small sips of sea foam, slow down when the car starts to stall, it helps if you have a helper to rev the engine when it sputters, keep pour ing in sea foam untill you have about an ounce left then dump this in all at once and stall the engine. let it sit for half an hr then start it up, It will smoke like hell, its supposed to, thats the carbon build up crud being burned off, take it out for a ride and do some 0-60 runs, then drive it normaly and you're good to go. The dirtier your engine the more it will smoke, smoke as in you cant see you're hand in front of your face lol. do it outside not in the garage!!
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It's recomended to drive it for no more than 200 miles before changing your oil if you use it in the crank case