Red Line SI-1 Complete Fuel System Cleaner

Pour one bottle in the tank to scrub injectors and intake valves clean — rough idle and lost MPG often clear up by the next fill.

Cleans fuel injectors, carburetors and intake valves in one tank.
Helps restore lost power, smooth idle and fuel economy from deposits.
Concentrated formula treats a full tank and is safe for regular use.

$17.47

On Amazon when we checked (June 22, 2026) — live price may differ.

By Patrick Smith · Updated July 11, 2026 · How we review · We may earn a commission from Amazon links.

Price when checked: $17.47; on Amazon, June 22, 2026
Best for: It worked best on high-mileage or rough-running engines; worst as a miracle expectation…
Biggest complaint: The recurring caveats are that results are engine-dependent — several users saw no change in mpg or…
Sources cited: 1; independent source

Reasons to buy

Users most often praise its high PEA concentration and report smoother idle and improved responsiveness on engines with real deposit buildup.

Reasons to skip

The recurring caveats are that results are engine-dependent — several users saw no change in mpg or drivability — plus premium pricing and a notoriously unpleasant odor.

Red Line SI-1 earns its shelf price on chemistry: it carries one of the highest concentrations of PEA (polyether amine) — the detergent that actually dissolves injector and intake-valve deposits — of any off-the-shelf fuel system cleaner. On oil and fuel forums, long-running threads keep landing in the same place: owners of high-mileage or rough-idling cars often report smoother running and better throttle response after a bottle, while owners of healthy engines running quality gasoline frequently notice nothing at all. Two smaller quirks come up repeatedly in user reports: it costs more per bottle than Techron or Gumout Regane, and the solvent smell is memorably foul — one user compared it to rotting fish. Use it as a periodic deep-clean, not a tank-by-tank ritual.

What buyers say

Our summary of recurring themes in customer reviews on the Red Line SI-1 Complete Fuel System Cleaner Amazon listing (read July 2026) — not quotes or endorsements.

Most praised

Users most often praise its high PEA concentration and report smoother idle and improved responsiveness on engines with real deposit buildup.

Most common complaint

The recurring caveats are that results are engine-dependent — several users saw no change in mpg or drivability — plus premium pricing and a notoriously unpleasant odor.

Worked best for

It worked best on high-mileage or rough-running engines; worst as a miracle expectation for well-maintained cars already burning detergent-rich fuel.

Frequently asked questions

How often should I use SI-1?

Most owners run a full bottle through a near-full tank every few thousand miles as maintenance. Red Line also rates it safe for continuous use at lower doses, which some forum users do.

Will it improve my fuel economy?

Only if deposits were costing you economy in the first place. Forum reports split cleanly: rough-running engines often improve, while healthy engines show no measurable mpg change.

What makes SI-1 different from cheaper cleaners?

Its high concentration of PEA, the active detergent proven to dissolve injector and valve deposits. Some cheaper cleaners contain far less PEA — or none — per bottle.