Thanks to its hydraulically actuated, electronically controlled unit injection system (HEUI), the 7.3L Power Stroke has some of the hardest-working engine oil in the world. Not only is it pressurized to roughly 60-psi for proper lubrication, but it also gets pressurized to 3,000 psi or more in the injection system’s high-pressure circuit. This extreme pressure builds a ton of heat, so it goes without saying that the oil cooler is a vital component in the sum of all the 7.3L’s parts. Luckily, the 7.3L’s oil cooler is typically as reliable as the rest of the rotating assembly, often lasting a couple decades before experiencing any issues (which seldom includes outright failure). However, nothing lasts forever. When we noticed a few oil spots under the driver side of our old-body-style (OBS) Ford workhorse, we knew it was time for an oil cooler overhaul. And being that this oil cooler lasted nearly 25 years, it may just be the last service it ever needs. Follow along for the tips and tricks you’ll need to know to tackle this fairly straightforward job in your own driveway.
Textbook Oil Cooler Leak
If you spot a few drops or a small puddle of oil under the driver side of the ’94.5-’03 7.3L Power Stroke engine, chances are pretty good it’s from the oil cooler. Hint: if the leak is discovered on the passenger side it’s probably from the dipstick tube adapter. The most common type of oil cooler failure is depicted above, where the outer O-rings fail, allowing oil to seep from the ends where the oil cooler presses into the headers.
Brace Yourself For A (Potential) Mess
To remove the oil cooler, start by draining the coolant and loosening the oil filter. Have drain pans ready to collect everything or things will get messy fast. To better access the pair of 10mm bolts in the front oil cooler header, you can pull the lower radiator hose. Three 10mm bolts connect the rear header to the oil cooler pad along the block. Before you loosen those, make sure to remove your block heater from the oil filter base.
Dislodging And Dropping the Oil Cooler
Even with all the mounting bolts broken loose, the oil cooler headers will likely both have to be pried free. To avoid damaging the front cover (what the front header connects to), start with the rear header. You can use a small pry bar or flat head screwdriver to separate it from the block. From there you can remove the oil cooler and both the front and rear headers as a single assembly.
Breaking Down the Oil Cooler
Next, discard the original front and rear mounting gaskets and begin the process of pulling the oil cooler housing (the tube) out of the headers. In our experience, it pays to place a small pry bar between the metal tab that’s riveted onto the oil cooler tube and the front header to force the two apart. The rear header isn’t usually as easy, so don’t be afraid to break out the rubber mallet for a little coaxing, but at the same time don’t Hulk-out. A new OE rear header will cost you more than $400, as this is the side that integrates the oil filter base.
The Culprit
The offending O-ring in our case was the outer O-ring positioned at the rear header. Instead of the rubber seal having round edges, it was flat. In addition, its exposure to the rusted oil cooler tube had allowed it to also begin rusting. The remaining three O-rings didn’t look so hot, either. We picked them all off of the oil cooler tube and started with fresh inner and outer versions. The inner O-rings carry Ford part number 1C3Z-6C610-BA, the outers are PN 1C3Z-6K649-BA and they can be had in all-inclusive oil cooler re-seal kits for between $60 and $80. Always stick with genuine Ford (or International) parts when performing this job. Think about it, the fact that the oil cooler O-rings can last a quarter of a century should be all the convincing you need to stick with factory components.
Reusing the Oil Cooler Tube (When Applicable) Saves Money
On 7.3L applications that see prolonged exposure to road salt, precipitation and humidity, the oil cooler tube itself can rot from the outside inward, requiring more than the simple re-seal we were able to get away with (note that the 7.3L’s oil cooler rarely ever fails internally). If you’re not as fortunate as we were and have to replace the entire oil cooler tube, a replacement from Ford will run you $200 to $250, depending on where it’s sourced (and that part number is 1C3Z-6A642-AA). Notice that the aforementioned inner and outer O-rings have been installed here, and you might also note that we cleaned the oil cooler tube, inside and out.
Reassembly
With the new inner and outer O-rings installed, thoroughly clean the gasket mounting surfaces on the front and rear header. Then lubricate the insides of the headers and O-rings (we used fresh engine oil), so as to not roll or tear the O-rings, and press the headers back onto the oil cooler tube by hand. Before you install the freshly O-ringed oil cooler, also make sure you clean up the mounting points for the headers on the block and timing cover. A Scotch-Brite pad and a die grinder work great for this.
Front & Rear Mounting Gaskets
These are the two mounting gaskets you’ll need to reattach the oil cooler headers to the engine. Even though Ford states they’re reusable, after 20-plus years of service it’s best to start fresh to guarantee leak-free functionality for the foreseeable future. We started with the front gasket (Ford PN F7TZ-6A636-AAA, shown on the right), positioning it between the front oil cooler header and the timing cover while installing the 10mm mounting bolts. We left the bolts loose until the rear gasket (PN F4TZ-6A636-A) and rear section of the oil cooler was reattached. Then all five mounting bolts were tightened and torqued to Ford’s 18 ft-lb spec.
Lift Not Required (But It Sure Helps)
You don’t have to put your 7.3L on a lift to change its oil cooler…but it helps. Also, don’t forget to reattach the lower radiator hose (if you removed it), top-off the coolant, reinstall the oil filter and top-off the oil when you’re done. If all went well, your 7.3L’s oil cooler should give you another 10, 15 or even 20-plus years of trouble free service.
Thinking your old 7.3L needs a wake-up call in terms of performance? Find out how to make power on a budget here.