STP Ultra 5 in 1 Fuel System Cleaner

STP Ultra 5 in 1 uses PEA detergent — confirmed at 10–25% in the US SDS — the chemistry class with the most independent research on injector and intake-valve deposits. A co-active alkyl aminoester at 1–5% is credited by the brand with combustion-chamber coverage, but that third zone is manufacturer claim only, no SAE paper or dyno test. Protocol: one 12oz bottle per 35 gallons every 4,000 miles. Community sentiment is strongly positive (4.6 stars, 1,942 reviews, 76% five-star through May 2026) — consistent with PEA's documented performance on injectors and intake valves.

Good fit for gasoline owners running non-Top-Tier fuel who want PEA maintenance chemistry at a mid-range price. Skip it if you always run Top Tier — the built-in detergent package already covers maintenance dosing. Skip it for mechanical-grade symptoms (misfires, stalling) — professional service is needed, not a pour-in treatment.

DANGER from H318 serious eye damage and H304 aspiration hazard. Goggles required; nitrile gloves warranted per H317. No inhalation H-code at mixture level — vapors are a concern only in an enclosed garage; pour outdoors. Do not induce vomiting if ingested — seek medical attention. No Prop 65 per the US SDS. The product combusts in the engine; exhaust is the environmental endpoint.