Transmission cooler upgrade for a Ford 7.3L
Atransmission is not something that most truck owners think about… until it fails, that is. The most common cause of failure in an automatic transmission is not age; it’s excessive heat. Towing, especially of heavy loads while in overdrive, produces heat. Sure, regular tranny fluid changes and towing in third can extend the life of the automatic in your Ford Super Duty, but a properly sized transmission oil cooler is the most important part of the cool-running automatic transmission equation.
Owners of ’ 99-03 Ford Super Duty trucks know that the 7.3L Power Stroke diesel engine is a good engine. Unfortunately, the 4R100 automatic could be a little tougher and these trucks are also plagued with factory tranny coolers that run a little on the small side. The ’99 to ’03 Fords with the 7.3 are fine for daily driving. However, the OEM cooler can be over-taxed while towing heavy loads and the heat that results can mean issues with the auto trans. Not to worry—there’s a solution and it involves some top-quality OEM parts.
John Ferguson at Domestic Diesel Service in Chino, California, offered to show us the solution. He’s a Certified ASE Master Mechanic and started in Ford's service department in 1996. He’s familiar with the Ford diesel lineup and the parts they use. His solution is to swap out the smallish 7.3L trans cooler for one of the larger units that were standard in the 6.0L Power Stroke-equipped trucks.
Now this is not a direct bolt-in, but it’s close to it. The fact is, the later model coolers will fit behind the grille of your 7.3-equipped truck, with a few minor modifications. The first of these modifications is the cutting and splicing of the rubber lines that run from your transmission to the original trans cooler. These lines are 3/8inch diameter and the new cooler takes ½-inch lines. Domestic Diesel offers a small parts kit with adaptor fittings to splice the two line sizes. (The kit also includes other required small parts). The fact that the cooler takes a larger line is not a problem; bigger is better, so there’s no issue with restriction of flow. In addition, the new cooler will have a slotted lower mount that will require either a fender washer over the two lower mounting bolts, or the use of the OEM 6.0L rubber bushings. Fender washers are in the small parts kit and work great. Also, they won’t deteriorate over time like the rubber will.
The lower splash cover under the bumper
must be removed and the installation should also be done with the grille off. This is not hard to do, as the factory makes these parts easy to take off for service and assembly reasons. Some will tell you to remove the front bumper, but with a swivel attachment you can get around this task and save time. From start to finish, this upgrade should take you from four to six hours, depending on interruptions and your comfort level.
Ford offers two different transmission coolers for the 6.0. The smaller one is good for all but the most strenuous towing needs. The larger cooler can be used too if you want to go for the ultimate cooling package for your transmission. Of course, being larger, it’s a little more work to get in, but it does fit without any major modifications.
We’ve seen reports of a 30-degree-average trans temp reduction when running unloaded. When towing, some have claimed as much as 60-plus degrees in temperature reduction over the stock trans cooler. These are subjective numbers and your results may vary. One thing’s for sure: a larger transmission cooler is sure to drop your running trans temps over the stock unit. UDBG
3 The stock transmission cooler for ’ 99-03 Fords with the 7.3L Power Stroke is smallish. Some would say it would make a nice upgrade for the power steering cooler, but the brackets make that problematic. Notice that the cooler has hard-line fittings....
2 The lower air dam and the power steering cooler are removed to install the transmission oil cooler. The power steering cooler can just be hung to the side while making the trans cooler upgrade.
4 Here you can see the coolers Ford selected for the 6.0L-equipped trucks (left and center) and the stock cooler for the 7.3L on the right. The smaller of the two late model coolers is a 26-row unit that has more than 124% more surface area than the...
5 This is the open lower mounting tab on the two 6.0-style coolers. A simple fender washer on the stock bolt will ensure this mount doesn’t come loose.
6 The transmission lines on the 7.3L trucks have crimped hard lines on each end, and a 3/8-inch flex section in the middle. These lines are cut and 3/8- to ½-inch adaptor fittings are installed to mate with the new cooler input fitting size. The new...
7 Here you see one of the 26-row coolers being installed in our test truck. This cooler has more cooling capacity than two of the stock coolers and is ideal for all but the most intensive heavy towing tasks.
8 The new ½-inch cooler lines are attached to the new transmission cooler with simple hose clamps.