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Regular price $199.99
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1994-1997 OBS CAN INSTALL USING THE SUPPLIED PARTS - simply remove your existing cooler, install the new cooler in the same location, and connect to existing lines.

Extend the life of your transmission efficiently and economically!


Thousands of automatic transmissions fail every year from overheating.  Whether you're towing a heavy load or driving in stop-and-go traffic, you risk overheating your transmission fluid.  When your transmission fluid reaches 200°, it starts breaking down.

• at 240° varnishes form and transmission life expectancy is halved.
• at 260° transmission internal seals and rubber parts harden; major damage starts.
• at 295° or above the transmission starts slipping, clutches burn, and carbon forms.

With each 20° drop in operating temperature, your fluid and equipment life doubles.  Installing a cooler before damage starts and by reducing the transmission fluid temperature by as much as 60° can greatly extend the life of your transmission.


Extend the life of your transmission, increase towing performance, and protect your vehicle's transmission with a simple to use addition to any towing set up.  The COOLERMAX transmission cooler is specially designed by DIESELSITE to be a reliable upgrade over your existing transmission cooler OR as an auxiliary unit used with your OEM cooler.

• -8AN inlet size
• 59,000 BTU rating
• 22.85" x 7.25" x 1.25" core
• Rated at 150 PSI working pressure and 750 PSI burst pressure
• Efficient 17-row stacked-plate core for optimal performance with minimal pressure loss
• JIC cooler fittings to 316 stainless hose barb adapters for corrosion prevention and leaks
• Universal mounting brackets to ensure a hassle-free installation; mount anywhere space permits
• Same bracket footprint as the Tru-Cool® 4739 transmission cooler while adding over 10,000 BTUs of cooling

Cooler can be installed with fittings in any direction.  Up, down or sideways depending on your application.  The optimal installation is with fitting facing up.  This will ensure all air is purged from the system and 100% of the cooler is used for heat exchange. 


The COOLERMAX transmission cooler can be purchased with cooler fittings only or with an optional installation kit to help save on time and parts collecting.  

The installation kit includes 6 feet of transmission hose, menders, clamps, zip tie mounting kit, and mounting hardware.

Please choose the appropriate fitting size based on your trucks line sizes when choosing your selection.

Frequently Asked Questions


Q: "I plan on a 27-30 TT next spring and with moving it in and out of camp grounds and my storage area on the military base, I'm worried the tru-cool won't keep the temp down."

A:  "I had the same concerns you do. I felt I had to have a cooler with a fan for stop and go traffic and times when I was not moving much air over the cooler. However, I did order the Tru-Cool Max and came out of my OEM tranny cooler and into the Tru-Cool and out to the tranny. Boy was I wrong in my assumption. Since I have installed the Tru-cool, I have yet to see temps over 165. I was seeing 195 - 200 unloaded in stop and go traffic. Just recently I went to Florida on vacation. I was pulling a camper right at 30 foot long. Everything with all gear and truck and passengers weighed in at 17,300 pounds. Tranny temps never exceeded 165 and it was between around 96-98 degrees outside. The Tru-cool works...period." --- James in Tenn

The previous question was pulled from a public Forum concerning this cooler


Q: What makes the Tru-Cool different or better than anything else?

A:  To answer this, you have to understand what different cooler designs there are in use.

The most common type is the "tube and fin". This style has small tubes that the fluid passes through and the tubes are surrounded by thin aluminum fins that cause passing air to turbulate or tumble over the tubes to pull heat away from them.

The next kind and far more efficient is the "stacked plate". This type uses flat hollow plates for the fluid to pass through. This increases surface air and the thinner area of oil increases the amount of heat transfer.

The third kind- that of the Tru-Cool Max - Is the "fin and plate". As the name implies, it uses the plates in the stacked plate design and the air fins of the tube and fin design and combines them for the most efficient type of air to liquid cooling transfer possible.

Q: I have added an additional cooler to my Powerstroke truck and I still see higher than expected temps. How do I check to see what is wrong?

A:IMPORTANT! The temps should be measured in the pressure port in the driver side of the transmission body. If you are measuring temps from a tee in the output line, temps will read about 30 degrees hotter than temps read from the pressure port.


  • Bring the transmission up to temperature. It needs to be at least 100 degrees for this test.
  • Turn the truck off.
  • Remove the rear line from the transmission and place it into a bucket or similar container so that you can measure volume of your flow.
  • Have someone turn the truck on.
  • At idle (in park), you should measure 32 ounces of fluid in your bucket - in 15 seconds or less. This is an absolute minimum number. A properly working transmission will flow that amount in about 10 seconds or less. You should not see ANY fluid pumping out of the rear transmission port.


  1. If you have the proper amount of flow, your transmission pump and coolers are working fine. SO, if you are running hot and have the proper flow (with no fluid coming out of the rear transmission port), you most likely have a mechanical problem causing high heat.  This could be torque converter slippage or one of many other internal problems. You may have to see a professional at this point to help diagnose the problem.
  2. If you do not have proper flow, OR you have fluid coming out of the transmission rear port, you either have a cooler blockage, OR a faulty cooler bypass valve. Here's how to tell.
  • Trace the forward transmission line to the front of the truck.
  • Remove the line from the 1st place it enters a cooler or the radiator (if so equipped).
  • Now, do the same flow test checking flow at this point.
  • There are two outcomes.
  1. The first is that you now have enough fluid flow- this means your cooler /coolers are partially blocked. To determine which cooler is plugged you would perform the same flow test through one cooler at a time.
  2. The second outcome will be that you don't have enough flow even with all coolers disconnected. This means you have an internal pump problem.

IMPORTANT! The outcome of this test assumes that you have NO fluid exiting the rear port of the transmission. If you perform a flow test with the coolers disconnected and you get fluid from the rear port on the transmission, your cooler bypass valve is bad.