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Diesel Tech Q&A: Towing with Older Diesels

Originally Published in Trailer Life Magazine

Towing with Older Diesels

Red letter Q

I drive a 1999 Ford with the 7.3-liter diesel engine and an automatic transmission. I pull a 2018 Keystone Hideout 21FQWE, which weighs 4,650 pounds (dry). There’s no problem with climbing hills or the weight of the trailer. My question is more about aerodynamics and miles per gallon. The Power Stroke feels like it’s pulling harder than it should when the truck is up to anything resembling highway speed, and depending on my right foot and the wind, mpg will be anywhere from 8 to 13.
Jade Parker

Green letter AOne of the hard truths in life is that as things get older, they don’t do perform like they did when they were young. Your classic Power Stroke is no exception. Another truth is the lighter the towed load, the better the fuel economy — and along with that, the smaller the aerodynamic drag, the greater the mpg. Taller, heavier tires and carrying any type of load in the bed also reduce fuel economy.

Anything that helps air move more efficiently around the tow vehicle and trailer increases fuel economy. How much of a gain is dependent on many variables, from weather and road conditions to the terrain and how the driver operates the vehicle. Usually, aftermarket “aero” add-ons that reduce wind “drag” don’t provide a big enough gain in fuel economy to make up for their cost until you’ve logged tens of thousands of miles at speeds above 50 to 55 mph, which is when aerodynamic drag starts rearing its head.

You don’t mention how many miles your old Super Duty has on it, or if the 7.3-liter Power Stroke has been rebuilt or upgraded in some way. If the injectors and turbo have not been upgraded, I’d highly recommend starting your search for better power and fuel economy with those two components. Fresh injectors (not bigger injectors) can instantly improve fuel economy.

“Most of our customers that have older, worn-out injectors and who upgraded to something like our Premium Reman Power Stroke Injectors do see an increase in fuel economy,” says Rykan Holder, owner of Holders Diesel Performance in Sarasota, Florida. “That’s because fresh injectors with all new parts mean the injectors are performing optimally and efficiently.”

A fresh Garrett turbo, or a rebuild of the one you have, with an upgraded compressor wheel should also improve your Power Stroke’s towing efficiency.

Red letter QI have a 1998 Chevrolet 6.5-liter diesel three-quarter-ton pickup used to pull a 25-foot trailer. The truck has less than 95,000 miles on it. How much do the tips you give for modern trucks apply to this one? I started working on Heath Diesel’s upgrades but could afford only the water-pump upgrade before the company sold out to DieselSite. I still want to do the chip upgrade and turbo-wastegate conversion, but I have to save up. In your opinion, would those be worth doing?
Steven Douglas

Green letter AIf the rest of the truck is in good mechanical working order, including the transmission, and you are happy with how it drives, other than not having quite the power you’d like, I don’t see any reason not to invest a few thousand dollars into engine upgrades.

There are a lot of upgrade components available for GM’s 6.5-liter turbo-diesel used in the 1992 to 1999 C/K pickups, with several aftermarket-parts suppliers providing components to help solve common weak points and improve power. Banks Power, Sinister Diesel, SS Diesel Supply and others carry common parts proven to give the 6.5-liter TDs longer life and more muscle. Replacing the turbo and intake with more modern, efficient and durable versions is the first step, along with replacing the stock engine computer (ECU) with one that has a 40- or 80-horsepower performance tune.

The 6.5-liter injectors have about a 100,000-mile life span, so replacing them with “marine” injectors will add about 40 more horses and smooth out how it runs. Like all diesels, when you provide more air, fuel, boost and timing changes, it makes more power.

You should also consider replacing and relocating the factory pump-mounted driver (PMD), the small black box mounted on the side of the injection pump. That is a well-known fuel-injection failure item because of heat issues. SS Diesel has an FSD Heat Sync kit that replaces the OEM PMD with an upgraded version and relocates it to a cooler area in the engine compartment.

The 6.5-liter TDs also had overheating issues that lead to cracked cylinder heads, so consider installing a quality all-aluminum radiator. Plan on spending $3,500 to $4,500 in parts to bring your 6.5-liter up to the level you are probably looking for to tow your trailer.

Red letter QWe are considering buying a 2010 Ford F-350 dually with a 6.4-liter diesel. I have read that this motor is not that good. What are the thoughts?
Joe Hunker

Green letter AThe 2008 to 2010 Navistar-built Ford 6.4-liter diesels were more reliable and had fewer catastrophic failure issues than the 6.0-liter they replaced but still had their own history of expensive-to-repair problems. Top among those is related to the emissions and the plugging of the diesel particulate filter (DPF.) More specifically, oil-dilution issues because some of the extra fuel dumped into the engine during the DPF regeneration cycle made its way into the oil pan. The DPF will plug up and need to be replaced, usually before 100,000 miles.

Another big concern with the 6.4-liters was the poor operation of the factory water separator and water contaminating the fuel. They also had a history of cracked pistons, lift-pump failures and leaks along sides and where the plastic tank ends meet the aluminum radiator, the oil cooler is prone to plugging up and failing, and the coolant system is known to have restriction and plugging issues starting with the twin exhaust gas recirculation (EGR) coolers. Failure of the emissions components and cracked turbo up-pipes are what led many owners to take the drastic measure of “deleting” the EGR system, despite that being against federal emissions laws.

Many Ford diesel technicians I’ve talked to say you can expect some type of “catastrophic failure” between 150,000 and 200,000 miles. Repair costs on the 6.4-liters are much higher than on the previous 6.0-liter Power Stroke, so that’s why you see owners selling them instead of investing in repairs when such issues arise. Ford designed the 2008 to 2010 Super Duties to have the cab pulled in order to effect engine repairs. This alone adds four to six hours to the labor costs.

If the 6.4-liter you are looking at buying has already had these issues addressed, it should be good for another 100,000 miles if well maintained. But if the truck’s service records indicate these issues have not been fixed, then I recommend you pass and look for a 6.7-liter Power Stroke (2011 to present), which is a far better truck in every regard.

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Have a Diesel Tech Question?

To ask Bruce W. Smith a question about maintenance, repairs or upgrades to your diesel truck, SUV or van, go to the Diesel Tech Q&A home page, scroll down to the Leave a Reply box and type in your question. Please include your full name and hometown.

Bruce W. SmithA respected automotive and RV journalist and longtime Trailer Life contributor, Bruce W. Smith has held numerous editorial titles at automotive and boating magazines, and authored more than 1,000 articles, from tech to trailering. He considers his home state of Oregon a paradise for RVing and outdoor adventure.

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