ACDelco radiator cap RC85 15 PSI — GM OE direct-fit replacement, spring-loaded seal

The ACDelco GM Original Equipment RC85 (15042975) 15 P.S.I. radiator cap is a direct-fit, spring-loaded cap that seals the cooling system and maintains the correct 15 psi pressure for compatible GM vehicles.

This genuine GM-recommended radiator cap replaces the factory-fitted component to keep the cooling system sealed, manage pressure, and allow coolant recovery between the radiator and expansion tank as temperatures change. Built to original equipment specifications, this ACDelco cap matches the form, fit, and function expected for GM vehicles, helping preserve cooling system operation and longevity through stable pressure control.

How does this radiator cap control coolant boiling point and pressure?

The cap uses a calibrated spring and valve assembly to hold the system at 15 pounds per square inch (P.S.I.) while the engine is hot. Holding this pressure raises the coolant boiling point compared to an open system, helping the engine run within designed temperature ranges under load.

• Calibrated spring valves set to 15 P.S.I. for consistent pressure control
• Seals the radiator filler neck or surge tank to prevent vapor loss
• Engineered to minimize unintended coolant evaporation and boil-over

What happens when the engine cools — will coolant be returned to the radiator?

Yes. When the system temperature drops and pressure falls below the valve threshold, the cap allows coolant to flow back from the expansion tank into the radiator. This automatic recovery helps maintain the correct coolant level without manual topping-off in many scenarios.

• One-way valve permits coolant return during cooldown cycles
• Maintains system fill level to reduce air pockets and hot spots
• Designed to work with vehicles equipped with an expansion/overflow tank

Is this ACDelco cap a direct replacement for my GM vehicle’s original part?

ACDelco GM Original Equipment caps are manufactured to GM specifications and listed as recommended replacements for compatible models. The RC85 (15042975) is vehicle-specific fit type, so matching the part number to your model year and engine application ensures correct fit and function.

• Manufactured to GM OE specifications for reliability and durability
• Vehicle-specific fit; verify part compatibility with your GM model
• Replaces the factory cap with matching performance characteristics

How do I know when the radiator cap needs replacing?

Replace the cap if you notice coolant loss, system overheating, or steam from the radiator neck. A failed cap can leak pressure, allow premature boiling, or fail to return coolant, so periodic inspection and replacement as part of cooling-system maintenance is advisable.

• Look for cracked seals, corrosion, or damaged spring action
• Symptoms include coolant leakage, frequent low coolant level, or overheating
• OEM replacement prevents mismatched pressures and inconsistent performance

Who is this for: The ACDelco RC85 15 P.S.I. radiator cap is intended for owners and technicians maintaining GM vehicles that list part number 15042975 or the RC85 spec. It’s suited to anyone wanting a factory-quality replacement that preserves designed cooling system pressure, supports coolant recovery, and matches GM original equipment standards. Choose this cap when you need a direct-fit, durable component that follows GM recommendations and helps avoid the issues caused by a worn or incorrect radiator cap.