Hayden Automotive Rapid-Cool Universal Add-On Transmission Cooler 9.5"×11" — Plate-and-Fin, Low Pressure Drop

Hayden Automotive 678 Universal Rapid-Cool is an add-on plate-and-fin transmission cooler kit sized 9.5" x 11" that reduces transmission fluid temperature for towing and heavy-load driving — not a direct OE replacement.

This compact Rapid-Cool kit is designed to be installed alongside your vehicle’s existing cooler to lower transmission fluid heat during heavy duty use. The unit uses a plate-and-fin core with Hayden’s patented internal flow geometry to maximize heat transfer while keeping line pressure loss low. The kit ships with the cooler, hose, and mounting hardware, plus 19 mm (3/4") barb fittings for positive hose attachment.

How does this add-on cooler improve transmission performance under load?

Adding an auxiliary cooler lowers running fluid temperatures when towing, hauling, or driving in hot conditions, helping fluids resist thermal breakdown and protecting seals and clutches. The plate-and-fin core increases surface area for heat rejection while internal turbulation stirs the fluid for better heat exchange without a big pressure penalty.

• Plate-and-fin core for efficient heat dissipation
• Patented internal flow path boosts heat transfer
• Minimal pressure drop preserves line pressure and shift quality
• 3/4" (19 mm) barb fittings ensure secure hose connections

What vehicles and towing setups are compatible with the Hayden 678?

This cooler is sized for light- to medium-duty applications such as pickup trucks, passenger vans, Class C motor homes, and travel trailers up to about 24 feet. It’s intended for systems with GVWRs as described and for towing loads up to approximately 5,000 pounds. Because it is an add-on cooler, it works with many factory transmission cooling circuits rather than replacing OE units.

• Suitable for pick-up trucks and vans
• Works well on Class C motorhomes and travel trailers to 24'
• Appropriate for GVWRs up to 24,000 lb and towing up to ~5,000 lb
• Designed as an auxiliary, not direct OE cooler replacement

How is the Hayden 678 built and what comes in the kit?

The Rapid-Cool 678 uses a compact plate-and-fin construction to deliver high surface area in a small footprint. Its patented internal turbulation creates turbulence to improve heat exchange without causing large pressure drops. The package includes the cooler core, hose, and mounting hardware so you have everything needed for an add-on installation.

• Compact plate-and-fin cooler core, 9.5" x 11" overall size
• Patented internal flow path to increase heat transfer
• 19 mm (3/4") barb fittings for secure hose attachment
• Complete kit: cooler, hose, and mounting hardware included

How difficult is it to install and what should I check before buying?

Installation is typically straightforward for anyone comfortable with basic vehicle plumbing: mount the cooler in a high airflow area, connect hoses to the transmission cooler lines or remote circuit, and secure fittings. Verify clearance, hose routing, and that your vehicle’s cooling capacity and existing connections match a 3/4" barb. Remember this product is not a direct OE cooler replacement; it’s intended as supplemental cooling.

• Mount where airflow is not obstructed (front of radiator or A/C condenser)
• Confirm 19 mm (3/4") hose compatibility with your lines
• Check clearance and protected routing to avoid road debris
• Follow torque and fitting recommendations in the installation guide

Who is this for: The Hayden 678 Rapid-Cool add-on cooler suits drivers who tow or haul regularly and need extra transmission cooling capacity without replacing the factory core. It’s a good fit for owners of pickups, vans, Class C motorhomes, and trailers under 24 feet wanting a compact, efficient cooling upgrade with included hose and mounting hardware. If you require an OEM-form direct replacement, choose a model specifically designed to match your vehicle’s OE cooler.