STP Oil Treatment 15 oz.

STP Oil Treatment 15 oz. is a proven engine additive formulated to protect and enhance the performance of motor oil in passenger vehicles and light trucks. Whether you're running a classic carbureted engine, a modern fuel-injected platform, or anything in between, this treatment addresses the reality that straight mineral or synthetic oil alone cannot fully combat carbon buildup, sludge formation, and wear-particle suspension. Mechanics and enthusiasts rely on oil treatments when extending drain intervals, operating in harsh conditions, or revitalizing an engine showing signs of varnish and deposit accumulation.

The STP Oil Treatment formula works by penetrating existing sludge and lacquer deposits, breaking them down into smaller particles that remain suspended in the oil and pass through the filter on the next service interval. The additive package includes detergent compounds and anti-wear agents that bolster the film strength of your base oil, reducing friction and heat generation at critical bearing surfaces and valve train components. At 15 oz. per bottle, one treatment is typically mixed into a standard 4- to 6-quart crankcase, creating a seamless integration without requiring oil drains or system flushes—making it an accessible maintenance step for both professional shops and DIY mechanics.

This product suits owners who want to restore lost lubricity in high-mileage engines, those operating under towing or sustained heavy-load conditions, and anyone preparing a neglected or inherited vehicle for reliable service. The treatment is compatible with all conventional and synthetic motor oils, making it ideal for interval maintenance between scheduled oil changes or as a restorative measure in engines showing elevated oil consumption or tappet noise. Simply add the contents directly to your oil pan or through the dipstick tube with the engine off, then run the engine for 5–10 minutes to circulate the additive throughout the crankcase.