Trans­mis­sion cooler up­grade for a Ford 7.3L

Ultimate Diesel Builder's Guide - - Contents -

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.

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