Hayden 679 Universal 11 Rapid-Cool Add-On Transmission Cooler - Better

In this review the Hayden 679 Universal 11 Rapid-Cool Add-On Transmission Cooler is evaluated for owners who tow heavy loads or operate large RVs and need lower transmission fluid temperatures. The bottom line: this is a compact, purpose-built add-on cooler that drops operating temps significantly and is meant for supplemental cooling rather than direct replacement of a factory unit. It stands out for its patented flow path design and solid build, making it a sensible upgrade for Class A motor homes, large travel trailers and trucks used for towing up to 10,000 lbs.

Key Features

• Compact plate and fin design: provides efficient heat transfer in a small footprint so it fits ahead of the radiator without excess space needed.
• Patented flow path design: increases heat transfer while minimizing pressure drop so transmission pressure and performance remain stable.
• 19 mm hose barb fittings: secure attachment reduces risk of leaks and simplifies hose routing during installation.
• Pre-drilled mounting brackets: allow straightforward installation and make it easier to position the cooler in front of the radiator or condenser.
• Complete kit contents: cooler, hose and mounting hardware are included so there are no missing parts when fitting the unit.

Who It's For

This cooler is best for owners of Class A motor homes, large travel trailers, 5th wheel trailers and trucks with GVWRs up to 30,000 lb who regularly tow up to 10,000 lb and need supplemental cooling beyond the factory setup. It benefits users who want an add-on solution that improves cooling without a major overhaul of the vehicle's existing cooler system.

It is not intended as a direct replacement for a factory cooler, so buyers who require an exact factory-fit swap should look for OEM-specific units. Also, those with very limited space where mounting ahead of the radiator is impossible may need a different configuration.

Pros & Cons

Pros

• Effectively reduces transmission temperatures, with customer reports noting drops around 30 degrees, improving transmission longevity.
• Solid build quality and secure 19 mm hose barb fittings that minimize leaks and feel durable under towing conditions.
• Patented internal turbulation boosts heat transfer with minimal pressure drop, so cooling improves without harming system flow.
• Includes hose and mounting hardware for a complete kit and easier installation.

Cons

• Designed as an add-on, not a direct factory replacement, so may not suit buyers looking for exact OEM swap.
• The compact size means for extreme heavy-duty continuous towing some users might prefer a larger cooler capacity.

Specifications

Size	3/4 in x 11 in x 11-5/8 in
Compatibility	Compatible with OEM cooler systems, add-on use only
Applications	Class A motor homes, large travel trailers, 5th wheel trailers
Towing/GVWR	Suitable for towing up to 10,000 lb and GVWR up to 30,000 lb
Fittings	19 mm thick-hose barb fittings
Design feature	Patented flow path design for increased heat transfer
Kit contents	Cooler, hose and mounting hardware

Our Verdict

The Hayden 679 Universal 11 Rapid-Cool Add-On Transmission Cooler is a practical, well-built supplemental cooler for RV and towing applications where temperature control matters. It delivers strong cooling performance, secure fittings and easy mounting, making it good value for owners who need an effective add-on rather than a factory replacement.

Frequently Asked Questions

Can this replace my factory transmission cooler?
No. This unit is designed as an add-on cooler and is not intended to be a direct replacement for factory coolers.

Will it fit my motor home or trailer?
It is compatible with OEM cooler systems and is suitable for Class A motor homes, large travel trailers and 5th wheel trailers with GVWR up to 30,000 lb.

Does installation require extra parts?
The kit includes the cooler, hose and mounting hardware so no additional parts are typically required for a standard add-on installation.