STP Super Concentrated Fuel Injector Cleaner

The active is a Mannich-class detergent — a nitrogen-containing fuel-soluble compound that targets injector and combustion-chamber deposits. It is not the polyetheramine chemistry that the most-studied independent research evaluates, and at 1–<5%wt it sits below the concentration range where the rubric treats a named active as "functional." The brand states the product unclogs dirty injectors and treats up to 21 gallons per bottle; community evidence on BITOG positions STP as a value/maintenance option rather than a deep-clean treatment, and there is no SAE paper or independent dyno test specific to this product. Protocol is one bottle every oil change or 4,000 miles.

Best fit for gasoline owners who run non-Top-Tier fuel and want a low-cost periodic maintenance dose from a long-standing mass-market brand. Skip it if you always run Top Tier certified gasoline — the OEM detergent package already covers maintenance dosing. Skip it for direct-injection engines with intake-valve carbon symptoms — the tank-route delivery cannot reach GDI intake-valve deposits, and the Mannich detergent class is not positioned for that use. Skip it and seek professional service if symptoms are severe (major rough idle, stalling) — one bottle of consumer treatment is insufficient.

SDS §2 is DANGER — H350 (carcinogen Cat 1A), H340 (mutagen Cat 1B), H361fd (suspected reproductive toxin), H304 (aspiration hazard), H332 (acute inhalation Cat 4), H336 (narcotic vapour effects), H315 (skin irritation), and H226 (flammable liquid). The Amazon listing carries a Prop 65 warning, and SDS §15 names benzene, ethylbenzene, naphthalene, toluene, and cumene as Prop 65 listed substances at trace concentrations in the carrier basket. Lungs tier is required (Beyond SDS) reflecting the chronic-hazard chemistry rather than the acute §2 H332 alone. Do not induce vomiting if ingested — seek medical attention. The product combusts in the engine; exhaust byproducts are the environmental endpoint.