If transmission overheating is a problem on your 7.3, the logical remedy is to increase the size of the transmission cooler to bring it to within normal operating temperatures, which is about 150 to 180 degrees (depending on the ambient outside temperature). Another option for maximizing your transmission temperature is upgrading the transmission pan size, but for now we’ll concentrate on the cooler.

“The 6.0 Ford is a very reliable transmission,” says Loren Taylor of Diesel Tech. “But if you take a 2003 7.3 and you get 60,000 to 100,000 miles out of it, you’re doing good. I’ve got a ’05 6.0L Excursion, and it’s got 174,000 miles. We dropped the pan, and it looked brand new. I think the 6.0L is just an all-around better transmission,” he said.

There are several transmission coolers on the market that get good feedback in the diesel communities, but if you want to stay true to genuine Ford products then our experts suggest a transmission cooler from a 6.0L, which you can purchase directly from your local Ford dealership.

If you compare Ford’s 6.0L transmission cooler to that of a 1999 to 2003 Ford 7.3 cooler, you’ll notice a whopping difference in size. In fact, the 6.0L cooler has approximately 2.5 times more surface area than the 7.3 cooler and it holds more oil than stock. The lines running into the 6.0 cooler are also larger, providing more flow (1/2 inch). That’s a huge difference, and it is definitely the source of early transmission heating issues on the 7.3L Ford. It doesn’t matter which brand of synthetics you use either; more surface area equates to better cooling performance. Period. Fortunately, the fix is easy and affordable. And in fact, the product comes backed by a Ford warranty. The 6.0L transmission cooler lists between $400 and $425 directly from Ford (part # 5C3Z7A095CA).

When the 6.0L Ford was introduced in 2004, it came with a sizeable cooler that truthfully should have been installed in the 7.3L engine too. But it wasn’t. Updating your 7.3L with a 6.0L cooler is something that can be handled at home using mostly common hand tools, and it takes about a day of your time if you have some basic mechanical skills. The most difficult part of the job is attaching the new fluid lines and chasing down 90-degree elbow fittings that aren’t supplied with the product from Ford.