6.0L Power Stroke Problems, Part 1: Oil Cooler

Jan 21, 2024

Despite all the publicity the 6.0L Power Stroke gets for blown head gaskets and exhaust gas recirculation system issues, this love-it-or-hate-it power plant's biggest failure point lies in its factory oil cooler. In fact, the oil cooler is the primary culprit behind most of the 6.0L's notorious EGR cooler catastrophes. When (not if) the oil cooler fails, the engine is essentially starved of coolant flow and engine oil temp sky-rockets. While this is a very bad thing for any engine, for the 6.0L Power Stroke—an engine that relies on highly pressurized engine oil to actuate its fuel injectors (i.e. HEUI)—this is about as serious as a heart attack.

The oil cooler loses its efficiency little by little as the tiny coolant passageways gradually become blocked over time. The blockage is primarily made up of a mixture of casting sand from the block and heads, along with suspended solids (reminiscent of gel) left behind when an incompatible coolant begins to break down. As this buildup continues to pinch off and then eventually block coolant flow through the heat exchanger portion of the oil cooler, oil temp begins to climb. Not only is this boiling hot oil no good for the injectors, high-pressure oil pump, turbocharger and engine bearings, but the blockage starves the EGR cooler of adequate coolant supply. Eventually, the welds in the EGR cooler's internal core will rupture. Sadly, many EGR cooler failures aren't traced back to the oil cooler that caused them—and the process starts all over again after a fresh EGR cooler is installed.

Below, we’ll take a look inside the oil cooler and discuss what's replaced during a rebuild, as well as show you how to prevent an oil cooler failure from taking your 6.0L off the road again. In Part 2, we’ll dive into the 6.0L's rampant EGR issues.

It's one of the most common failures a 6.0L Power Stroke faces, and one that can lead to a myriad of other problems (a big one being an EGR cooler failure). Trouble is, oil cooler failure is very hard to detect unless you’re viewing the engine's oil temp and coolant temp in real-time as you drive. A temperature difference of 15 degrees or more between the two parameters usually means the oil cooler is in the early to moderate phase of plugging. It doesn't get better on its own, and oil temp only climbs higher from there. When EOT gets hotter than 240 degrees F, it's definitely time to replace the oil cooler, before serious damage is done and the factory PCM begins to de-fuel the engine—which happens around 255 degrees.

To pull off an overhaul of the 6.0L's oil cooler, it behooves you to go with OEM parts (some aftermarket components don't hold up nearly as well). For folks that aren't exactly thrilled with the idea of installing the same parts that just failed prematurely, we don't blame you. But don't worry, if you read this article until the end we’ll show you how you can keep a factory oil cooler alive indefinitely. Ford's oil cooler rebuild kit carries part number 3C3Z-6A642-CA and comes with a new heat exchanger, pump inlet strainer and every gasket, O-ring and seal you’ll need.

As part of the 6.0L's compact packaging, the oil cooler sits at the front of the lifter valley, within the block. But one look at the lifter valley and you know a lot of work lies ahead in order to access (and ultimately remove) the oil cooler. Components like the turbocharger, intercooler piping, fuel filter reservoir, oil filter housing, intake manifold and EGR valve all have to be removed. Here, the oil cooler is being rebuilt in addition to addressing a blown head gasket and a blown EGR cooler, the latter of which was likely caused by a plugged oil cooler.

Once out of the lifter valley, the oil cooler's heat exchanger has to be separated from the oil cooler cover. This is done by placing the cover's edges on two blocks of wood (or something similar), with the heat exchanger allowed to hover off the ground or working surface. After the oil cooler mounting bolts are out, a 21mm socket and hammer are recommended to handle the dirty work. Tapping on the oil cooler's inlet and outlet ports with the socket breaks the heat exchanger loose from the cover.

The heat exchanger portion of the oil cooler is at the epicenter of any 6.0L oil cooler failure. Gasket, O-ring and seal failures are actually very uncommon, but everything needs to be replaced once you break the seal. Once removed from the engine and separated from the oil cooler cover (which is reused), a lot of folks cut the heat exchanger open to see the coolant passageway blockage for themselves. In engines that saw oil temperature crest 240 degrees F, the pathways are almost completely sealed off with sludge.

There are nine O-rings, three gaskets and one seal included in Ford's oil cooler rebuild kit, which means every fluid seal is replaced—and we’ll note that Navistar's step-by-step instructions are highly detailed so nothing gets mixed up during assembly. Here, the new outlet and inlet port O-rings are being installed (there are two per port, a small one and a larger one).

With fresh O-rings installed on both the new heat exchanger and the factory oil cooler cover, the cover is aligned and pressed onto the heat exchanger. Once the O-rings are fully seated, the mounting bolts can be reinstalled. Important note: never overtighten the small fasteners that go into the oil cooler. Ford has a torque spec for every one of them…use it! With the new pump inlet strainer in place within the block, engine oil should be topped off, preferably with a synthetic oil such as Amsoil heavy-duty synthetic 5W-40, followed by the install of the rebuilt oil cooler. Last tip: Always make sure to inspect the IPR valve and EGR cooler when you travel this deep into a 6.0L Power Stroke. It's a lot of work to get here—so you don't want to be doing it twice.

So how do you keep the 6.0L's oil cooler from failing again? You remove debris and other contaminants from the cooling system by installing a coolant filtration system. A kit like the one shown here from RCD Performance is a by-pass style system, where a small portion of engine coolant is filtered at a time and all suspended solids or chunks of debris are trapped in the filter. A coolant filtration system keeps the coolant passageways within the heat exchanger from plugging again. Just make sure to replace the filter every 500 to 1,000 miles in the early going—and feel free to cut the filter open before you discard it. You’ll be surprised with how much "stuff" you’re pulling out of the cooling system.