Mishimoto Transmission Cooler for Dodge Ram 2500-5500 (2003–2009) — Silver, 48‑Row High‑Capacity Core

The Mishimoto MMTC-RAM-03SL is a direct-fit, high-capacity transmission cooler that replaces the factory unit on 2003–2009 Dodge Ram 2500–5500 Cummins trucks to radically improve fluid cooling and serviceability.

Factory transmission coolers in Ram trucks were designed for everyday driving, not sustained heavy towing or fleet duty. Mishimoto redesigned the MMTC-RAM-03SL as a bolt-in replacement that installs in the original mounting location using the stock bolts while delivering far greater core volume, fluid capacity, and long-term reliability. It pairs a heavy-duty 48-row stacked-plate core with serviceable components and upgraded fittings to address common failure points found on high-mileage diesel trucks.

How much more cooling capacity does this cooler provide?

The MMTC-RAM-03SL dramatically increases both core volume and how much transmission fluid the cooler holds, reducing operating temperatures during heavy loads and repeated towing. Those gains translate to a cooler, more stable transmission under stress.

• 212% increase in core volume over the OEM cooler
• 244% increase in fluid capacity compared with stock
• 48-row stacked-plate core for improved heat transfer
• Compact footprint that fits the factory location (26" x 10.94" x 0.87")

Does it fit my Ram and how hard is installation?

This unit is engineered as a direct replacement for 2003–2009 Dodge Ram 2500, 3500, 4500, and 5500 trucks with 5.9L or 6.7L Cummins and compatible with 47RE, 48RE, and 68RFE transmissions. Installation is simple because the cooler uses the original mounting position and requires only basic hand tools and the included hose components for a clean swap.

• Direct-fit design uses two factory bolts in the stock location
• Compatible with 5.9L and 6.7L Cummins models (2003–2009)
• Works with 47RE, 48RE, and 68RFE transmissions
• Includes stainless-steel hose barbs and SAE J1532-rated hose for permanent connections

What serviceability and durability improvements does Mishimoto offer?

Mishimoto focused on the parts that commonly fail on older Rams: the thermostat and quick-disconnect fittings. The cooler features a removable, independently replaceable thermostat and stainless-steel fittings so you can avoid seized OEM connectors and perform maintenance without replacing the entire cooler.

• Fully serviceable thermostat accessible from the top port
• Replaceable thermostat avoids OEM closed-failure issues
• Stainless-steel CNC-machined hose barbs replace corrosion-prone quick-disconnects
• SAE J1532-rated transmission hose included for long-term reliability

Can I run this cooler full-time in hot climates or heavy-duty applications?

Mishimoto includes a stainless-steel bypass plug that lets owners lock the cooler in a constant full-flow configuration when desired, providing flexibility for extreme environments or continuous heavy loads. This feature enables operators to choose maximum cooling or retained normal operating dynamics as conditions require.

• Stainless-steel bypass plug allows constant full-flow operation
• Thermostat remains serviceable if seasonal or usage changes are needed
• 48-row core maintains consistent cooling during sustained towing or fleet cycles
• Robust construction intended for working trucks and high-mileage vehicles

Who is this for: The MMTC-RAM-03SL is designed for Ram owners who tow frequently, operate trucks in fleet or commercial settings, or who want a durable transmission cooling upgrade for high-mileage 2003–2009 5.9L and 6.7L Cummins trucks. If you need a drop-in replacement that improves cooling capacity, eliminates seized OEM fittings, and makes routine service simpler, this cooler is built for you.