Winston Churchill was known for his phrase, "a riddle wrapped in a mystery inside an enigma." At one point, that expression might have applied to a mysterious problem with the Ford Power Stroke 6.0L diesel. But just as Churchill noted, perhaps there's a key to solving this issue.
Initially, the problem appeared to be recurring failures of head gaskets. Some mechanics pointed to the number of head bolts as the cause. Other technicians felts it was due to the design of the EGR cooler. But the riddle remained unsolved, the cause a mystery.
In further efforts to get crack this enigma, samples of the coolant were drained out and allowed to sit still. Once a fine silt settled to the bottom, both the enigma and coolant finally became clear. Additional examination of several faulty heat exchangers (for both the EGR and oil system), revealed clogging from murky coolant, with further confirmation by comparing temperature differences between oil and coolant. This obviously indicated an issue with the coolant system, but one mystery still needed to be unraveled. Where was the silt coming from? And more important, how to keep it out of the system?
According to a number of diesel technicians we contacted, the source of the particles is residual sand from the casting of the 6.0L engine blocks, which can leach out from the metal lining and into coolant passages of the water jacket. As this sediment plugs up the oil cooler, the problem gets compounded. Less coolant flows to the EGR cooler, and the engine runs hot. Then the fluid begins to break due to the high temps, and the thin vanes of the EGR cooler suffer damage as well.
This domino effect can turn into some costly repairs—or even a total loss of an engine. A rebuild kit for a heat exchanger sells for about $400, not counting some nine to 12 hours of labor to install.
Worse yet, if you don't catch this problem in time, a 260-degree oil temp will max out gauge on coolant temp. And when you hit 300 degrees, just about every plastic part under the hood will melt. At that point, the engine can't be fixed, and requires replacing.
What's the key to solving this riddle? Simple: install a coolant filter. That, and following a few other maintenance tips.
Several aftermarket companies offer coolant filters, and are fairly similar in configuration. The one we used from BD Diesel took about hour to install.
On this particular unit, it's not mounted on the front in front of the water pump, partly because there's not enough room.
Instead, the filtration system is passive, and doesn't filter every pass of fluid, since the feed line is from a T-fitting off the heater system. There's an advantage to this setup, though. In the unlikely event there's a restriction in the line, it can't cause any damage to the engine.
In addition to being mounted in-line with the engine coolant hoses, the BD Diesel system includes a filter head, spin-on filter, mounting bracket, hoses, clamps, fittings, and mounting hardware, along with a bypass valve to make changing the filter easier. Other brands of coolant filters have similar components, but with slight variations in quality and layout. But they're all designed to do the same thing: keep your coolant clean and flowing.
How about those cooling system tips mentioned above? First, make sure you're using the correct type of coolant for diesels, as it has a conditioner that regular automotive green coolant lacks. This additive is not only anti-corrosive and improves longevity, but also prevents cavitation (bubbles that implode, pitting the outside of the cylinder walls and eventually eroding into the combustion chamber).
In addition, replace the filter, along with draining and flushing the coolant system, at the manufacturer's recommended intervals, if not sooner when operating in extreme temperatures.
Note too that radiator caps on the 6.0L can be mystery, as well. A defective cap that's venting a white, milky fluid can be mistaken for a blown head gasket. Installing gauges to monitor the variance between the oil and coolant temps is a good idea, because a difference of more than 13 degrees might indicate that your heat exchanger is not functioning properly, so you can catch a coolant system problem before it causes serious damage.
Last but not least, take a small sample of coolant from time to time and let it settle out. If you spot any sediment, shorten your service intervals and flush the system more often. It's no guarantee that sludge won't form, but at least you now have a solution to this riddle.