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Oil Cooler Replacement: 7.3L Power Stroke

Addressing One of the Venerable V-8’s Most Common Leak Points

Not unlike other aging diesels, as the 7.3L Power Stroke grows older it begins to develop oil leaks. As the years roll over, you’re bound to encounter a small leak from the dipstick adapter, a drip-drip from the oil cooler, or the dreaded seepage from a rusted out oil pan. Luckily for the owner of the ’97 F-350 in this article, a small oil puddle was discovered on the driver side of the engine, where it was quickly traced back to the oil cooler. Upon closer inspection, the outer O-rings had failed, meaning a re-seal was all that was in order, not complete replacement ($68 vs. roughly $300).

Regardless of cost, the oil cooler must be removed to solve the problem. Fortunately, it’s a relatively simple job that a even a novice could tackle at home. With a few simple hand tools, a couple drain pans, and the right replacement parts from Riffraff Diesel Performance, we were able to handle the job in three hours’ time. While a leaking oil cooler is more of a nuisance than a major issue, a few drops of oil will eventually turn into a puddle under your ’94.5-’03 Ford. For that reason alone, it’s best to address this pesky problem before it worsens. Follow along to see how we did it.

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After more than 217,000 miles and nearly 24 years of loyal service, we’d say the factory oil cooler had a pretty good run aboard this 1997 model year 7.3L Power Stroke. Finding a wet spot where the oil cooler housing slides into the rear header (also known as the oil cooler filter adapter or oil filter base) or front header is a telltale sign that the outer O-ring has failed. Early on in the failure, engine oil leaks past the O-rings when it’s cold, but stops leaking once warm (when the O-ring swells). Although you can get by with a leaking oil cooler for quite a while, the problem will only get worse until it’s addressed.
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Positioning a clean 5-gallon bucket under the radiator, we got started by draining the engine coolant. Had the engine been due for fresh coolant, this would’ve been an opportune time to add it, but as it turns out the Cat extended life coolant (ELC) being drained here was only a year old.
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Next, the oil filter was loosened up, the oil from the cooler and filter base were allowed to drain for several minutes, and then the filter was removed from the filter base (which doubles as the rear mounting point, or header, for the oil cooler housing). While an oil cooler rebuild is also a convenient time for an oil change, the oil being used in this engine only had 1,500 miles on it. The filter would be reused and the oil level topped off with fresh 15W-40 at the end of the install.
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A 7.3L’s log-style oil cooler housing attaches to the engine via a front header bolted to the front cover, and a rear header that attaches to the oil cooler pad at the back of the block. Of the two mounting locations, the front header is more difficult to access. On both OBS and Super Duty 7.3L’s, removing the lower radiator hose makes accessing the bolts much easier.
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All mounting bolts for the oil cooler headers call for a 10mm socket, and there are two bolts that secure the front header while three exist in the rear. Prior to turning our electric impact loose on the rear header bolts, we disconnected the block heater from the oil filter base, as well as its retainer and cable.
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With all bolts loose and the oil cooler’s headers still attached to the front cover and rear of the block, you can unthread the bolts completely and remove the oil cooler as a complete assembly by carefully prying on it. Use a pry bar or flat head screw driver to break the rear header free from the block. Prying between the oil cooler housing itself and the block may be necessary for an additional nudge in this process.
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Make sure you have a drain pan ready to catch additional coolant when you dislodge the oil cooler from the block. Trust us, things can get messy in a hurry. We used a 5-gallon bucket to catch as much fluid as possible, but in the end we still had to break out the oil dry.
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To free up more space for removing the oil cooler, we disconnected the truck’s EGT thermocouple from the exhaust manifold. Pulling the probe and moving the line out of the way also rules out the possibility of damaging it while wresting the oil cooler back into place later.
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To help separate the oil cooler housing from the front header, we used a large flat head screw driver between the metal tab and the header to pry the aluminum base free. Once we saw movement, we pulled on the oil cooler tube while simultaneously twisting the header until the two had been separated.
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The original mounting gaskets don’t always come off with the oil cooler, so you may have to go back and remove them from the front and rear header. Here, the OEM gasket for the front is shown up top (PN F7TZ-6A636-AAA) while the rear gasket is on bottom (PN F4TZ-6A636-AA).
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We did not have the same luck when removing the rear header from the oil cooler housing. After our efforts to pry, pull, and twist the tube free had failed, we resorted to our trusty rubber mallet. While the headers are fairly stout pieces, they are made of aluminum, so don’t get too carried away (a new rear header will run you more than $400 at the local Ford dealer).
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Fortunately, we didn’t have to replace the oil cooler housing itself. On a lot of trucks that live in the rust-belt, the oil cooler housing will rust from the outside in, requiring complete replacement. Because ours was reusable, we were only out $68 thanks to Riffraff Diesel Performance’s oil cooler seal kit. If you find that you need a brand-new oil cooler housing during this job (or you want to start with a fresh one for peace of mind), Riffraff keeps that in stock, too. It carries part number 1C3Z-6A642-AA and retails for approximately $225.
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If you’ve spent much time around 6.0L and 6.4L Power Strokes, you know that they’re notorious for cooler failure due to plugged coolant passageways. This is never the case with the oil cooler that was employed on the 7.3L. Its circular internal coolant passages are considerably larger than what is found in the stacked-plate versions used in the 6.0L and 6.4L.
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With anything mechanical, we like to see parts go back on the same way they came off. As creatures of habit, we marked the oil cooler housing with a B (for back) to signify that this end had been installed at the rear. In the end, the oil cooler housing isn’t a directional flow design, so it doesn’t matter which way you install it.
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This is what most failed oil cooler O-rings look like: hard, flat, and corroding. At both ends of the oil cooler, the outer O-rings (which is essentially what keeps oil from escaping the oil cooler) were toast. Notice that the O-ring is rusting.
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Next, everything took a trip through the parts washer. To get the grime and debris off of the bases, a wire brush was employed. Once the oil cooler housing was clean, we used compressed air to make sure each internal coolant passage was free of solution or debris.
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To ensure a good seal during reassembly, we took a die grinder equipped with a Scotch-Brite pad to all the oil cooler’s mating surfaces. This included both the front and rear headers, along with the rear pad on the block and the gasket surface on the front cover.
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Once the O-rings are in their respective grooves, they need to be treated to a very liberal amount of lubrication (we used fresh 15W-40). If they’re left dry you could roll or cut one while pressing the headers onto the oil cooler housing. A healthy coat of fresh oil was also added to the inside (outer edge) of the front and rear headers.
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With everything lubed up, each header was pressed back onto the oil cooler housing. For correct alignment, we simply lined up the notch marks present on the headers with the metal tabs on the oil cooler housing.
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Bolting the cooler assembly back on the engine consisted of installing the new front cover to front header gasket first, followed by its two header mounting bolts. Both bolts were left loose until the rear header was reattached to the block.
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Similar to what we did up front, the fresh rear header gasket was positioned on the pad on the block, the rear header set in place, and the mounting bolts reinstalled. At this point, we ran the three rear headers bolts and two front header bolts in just past hand tight.
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Then we broke out the torque wrench and looked up Ford’s specification for the oil cooler bolts. After torquing each one to the recommended 18 ft-lb specification, we reconnected the block heater and reinstalled the EGT thermocouple in the exhaust manifold.
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The final steps of the install included topping the oil filter off with fresh oil and threading it back onto the filter base, topping off the coolant, and then starting the engine and checking for leaks. There’s no telling if this 7.3L or the truck it’s powering will survive another 24 years of use, but the oil cooler most likely will!

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