The Ford Power Stroke 7.3L is a mighty engine, especially if you need maximum torque and horsepower for long hauls. But it does have a few weak links. They become especially evident when towing, as cargo weight can push transmission temperatures into the stratosphere.
| The 7.3L Ford is a great truck, but the transmission can overheat with regular towing. A simple fix is swapping in the transmission cooler from a 6.0L.
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.
Transmission Pans
Since we are talking about lowering the transmission temperatures, we can’t overlook the stock transmission pan size…it’s small. Since you will be increasing the size of the cooler, it would be wise to increase the size of the transmission pan as well, readily available from the aftermarket. The PML E40D/4R100 increases the pan’s capacity by 3.5 quarts. It retails for less than $250. But the crown jewel might be the Mag-Hytec 4R100 that fits all 7.3L Fords and retails for about $350. It can hold 7.6 more quarts of fluid than stock, and it’s very rugged, intended for off-road use.
| 7 The lower mounting bolts that were removed from the stock unit will not work on the new cooler. You must buy longer bolts.
Any way you go, increasing the size of the cooler should be accompanied by increasing the size of the pan as well to see noticeable degrees of cooling. Temperature drops as low as 20 or 30 degrees when towing are typical.
We spent a few hours at Diesel Tech in California to learn more about the upgrade and to follow along as David Briggs explained the process in detail. The owner of our test vehicle saw immediate temperature decreases thanks to this quick fix.
Here’s an overview of the installation on a 2002 F250 4WD that tows a large enclosed motorcycle trailer.
The DIY Plan
There are a few things that you should know before you begin the upgrade. The cooler from Ford does not come with any mounting hardware.
You don’t need a lift to perform the installation, but if you use jack stands, be sure they are secured in place and the vehicle is properly blocked.
As for tools, you will need a standard pair of pliers, 8mm and 7mm socket (for clamps), a Phillips head screwdriver, hose cutter, plumbers pipe thread sealant or tape, tie-straps, two 90-degree elbows (step-down 1/2 to 3/8), which can be purchased at any industrial supply shop.
You can use an impact on the bumper, and a quarter-inch impact works great for getting into the tight spots.
You will have to buy two long bolts for the lower cooler bracket, because the stock bolts are too short.
You will also have to purchase 1/2-inch oil lines into the new cooler. It’s best to buy more than you’ll need, and try to find fluid lines that don’t chafe.
There is no modification of the truck at all. This is a completely bolt-on upgrade. Plan on three to four hours of work if you’ve never done this installation before.
