AP Astro Pneumatic Tool Company Number-41 Radiator Test Cap for Late GM & Ford — Direct-Fit OE Style, Spring-Loaded Seal

The AP Astro 7858541 Number-41 radiator test cap is a direct-fit replacement cap engineered to restore correct cooling system sealing and pressure control on late-model GM and Ford engines.

This precision-made radiator test cap from Astro Pneumatic Tool Company (AP) replaces worn or missing caps to help maintain correct coolant system pressure and reduce fluid loss. Manufactured in Taiwan to compact dimensions, the cap matches OE-style fitment and is ideal for garage technicians, fleet maintenance, and DIY enthusiasts working on late GM and Ford vehicles that require a Number-41 style cap.

Which vehicles and systems does this Number-41 cap fit?

The Astro 7858541 Number-41 cap is intended for late-model General Motors and Ford cooling systems that specify a Number-41 style cap. It is built to the common size and sealing profile used on those applications, providing a straightforward replacement when the original cap is lost or damaged.

• Direct fit for late GM and Ford radiator necks requiring Number-41 specification.
• Compatible with closed cooling systems using spring-loaded pressure caps.
• Used as a service or spare cap in repair shops and maintenance fleets.

How does this cap help with cooling system performance?

A properly sized radiator cap maintains the cooling system's designed pressure, which raises the boiling point of the coolant and helps avoid localized boiling and boil-over during operation. The Astro cap restores the mechanical seal and spring function that prevent coolant loss and air entry into the system.

• Restores the intended pressure boundary of the radiator filler neck.
• Prevents coolant evaporation and loss under normal operating temperatures.
• Helps reduce air intrusion that can cause hot spots and reduced heat transfer.

What are the product dimensions, origin, and package details?

The AP Astro 7858541 cap ships in compact packaging suitable for retail shelves or repair kits. It is a lightweight replacement part, produced in Taiwan and sized to the Number-41 specification for accurate fit and function.

• Package dimensions: 6.3 cm L x 10.3 cm W x 12.0 cm H.
• Package weight: approximately 0.2 lbs for easy inventory handling.
• Country of origin: Taiwan, manufactured to industry tooling standards.

How should I install and inspect the replacement cap?

Installation is a simple twist-on procedure after the radiator has cooled. Inspect the cap seating area and the cap's rubber gasket and spring before installation to ensure a reliable seal and correct pressure response.

• Allow the engine to cool before removing the old cap to avoid scalding.
• Check the filler neck for corrosion or damage; clean before installing new cap.
• Verify the cap’s spring and gasket compress and reseal under light pressure after installation.

Who is this for: The Astro 7858541 Number-41 radiator test cap suits professional technicians, mobile mechanics, and vehicle owners maintaining late-model GM and Ford cars and trucks. It’s an appropriate spare part for service centers or fleet shops needing an affordable, OEM-style replacement cap that restores proper coolant system sealing and pressure control.