Mishimoto Oil Cooler Review 

Your truck’s transmission is the heart and you need to ensure that it runs all good. Now if you are an owner of a 2003-2009 Dodge Ram 5.9L/6.7L Cummins or any dedicated tow vehicle or hardworking fleet truck, or a daily driver with a liking for the drag-strip or something that sort, you are lucky because Mishimoto has developed a direct-fit transmission cooler just for your vehicle.

Mishimoto MMTC-RAM-03SL

Product Details



Mishimoto (CHINA)



Item Weight

8.5 pounds




6061 Aluminum

Liquid Volume

6.7 Liters

How We Tested

We bought a Mishimoto MMTC-RAM-03SL automatic transmission oil cooler and used it in our 2003 Ram 3500 dually with 5.9 Cummins. Then our expert product reviewers along with expert mechanics have tested the product and mentioned the pros and cons of it and compared the product with the other available transmission oil coolers. Our experts have also rated this product on the scale out of 10 dividing each catagory.

Our Ratings (Out Of 10)



Ease of Installing


Build and Durability


Electrical Output


Customer reviews




Our Driving Experience


Mishimoto Oil Cooler Review

Potential Pros


  • The transmission cooler is exceptionally well compared to the other ones available in the market because it utilizes a stacked plate core for durable and powerful cooling.


  • It has a massive 212% greater core volume,


  • The transmission cooler comes with a 244% increase in fluid capacity, which is relatively better than the other coolers and it is a huge improvement over stock.
  • The Mishimoto transmission cooler is significantly larger than the stock cooler you get


  • Mishimoto spares you the trouble of having to remove seized fittings as they made this cooler even simpler to install and maintain.


  • You may go right to the point with the stainless steel hose barb fittings that are CNC-machined and supplied.


  • You may connect the stock soft-line to the Mishimoto cooler by removing the quick-disconnect connections and using these fittings together with the transmission cooler hose that comes with the kit.



Solves All the Major Problems Regarding Thermostat


  • The Mishimoto thermostat in your 2003-2009 Dodge Ram Cummins transmission cooler is fully serviceable and easily bypassed for constant cooling unlike the default ones which had the issues of returning hot fluid to the transmission when the thermostat fails.


  • In just a few minutes, you may easily service the thermostat by using the port at the top of the cooler which is like a very handy addition to the exclusive product.


  • If a thermostat fails, it is not necessary to replace the complete cooler but instead, you can buy replacement thermostats separately as it is available


  • While owners in hot climates have the option to bypass the thermostat by swapping it out for the included stainless-steel bypass plug, owners in cold climates can still take advantage of the thermostat’s quick warming times.



Potential Drawbacks

  • In certain climates or driving conditions, the transmission cooler may be too efficient and this may lead to overcooling of the transmission fluid. This situation could negatively impact the transmission’s performance and longevity. So, monitoring fluid temperatures and using a thermostat may be necessary to prevent overcooling.




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