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Short Summary
Main recommendation: SeaFoam fuel system cleaner, used through the intake (not the fuel tank) with the included red hose, produced visible carbon reduction on the pistons of a 2008 Honda Civic Si with 125,000 miles in this test. The creator reports it as the first cleaner in his tests to show measurable results, based on borescope comparisons of all four cylinders before and after a single 5-minute treatment.
Key Points
- The product was applied through the intake before the throttle body, using the included red hose and spray nozzle, which avoids removing vacuum lines or risking hydro-lock.
- Before-and-after borescope footage through the spark plug holes showed reduced carbon around the piston edges in all four cylinders, with the piston ring area looking cleaner.
- The spark plugs were not fouled after treatment, which the creator notes as a common concern.
- Results were visible but not complete: the piston heads were not fully squeaky clean after only one 5-minute treatment.
- The creator states he bought the products himself and received no sponsorship; his earlier cleaners on a truck with similar mileage had not shown comparable results.
Details Worth Noting
- Concrete instructions: Warm the engine fully to operating temperature. Remove the rubber intake hose before the throttle body, loosen the hose clamp, insert the red SeaFoam hose, and retighten the clamp so the intake is sealed. Start the engine and hold it at about 1500 RPM while spraying the full can (the bottle says about 5 minutes to empty). When the can is nearly empty, hold the nozzle down, shut the engine off, and release the nozzle once it stops. Remove the hose, retighten the intake and clamp to prevent vacuum leaks. Let the car sit 5 to 10 minutes, then restart and run it until the exhaust smoke stops, rev briefly to break up deposits, and drive aggressively as the label instructs.
- Exhaust smoke begins about 10 seconds into spraying and was substantial during the process; the creator said it would clear afterward.
- The creator used about 90% of the bottle, and suggests waiting for the engine to cool before inspecting with a borescope.
- Test scope was a single application on one engine; the creator explicitly says it does not match the cleaning from a head-gasket-style repair and plans to test other cleaners.
- The creator mentions he previously used a SeaFoam product in a lawn mower video, shown briefly for comparison.
Bottom Line
Based on this single borescope comparison, SeaFoam applied through the intake cleaned carbon from the piston edges in all four cylinders of this Honda, but it did not fully clean the piston heads, so one treatment should be read as partial improvement rather than a complete carbon removal.
