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10 Things to Know Before Buying a Diesel Truck

Are diesel trucks better than gas? Are they worth the extra expense? Here are 10 things to consider when deciding to go diesel.


Diesel trucks are America’s workhorses: these machines move enormous loads thanks to a generous serving of low-end torque. And all the while, they return better fuel economy than gas models.

Choosing the diesel engine, whether it’s in a midsize pickup or a heavy-duty full-size truck, costs more money. So, are diesel trucks better than gas? Are they worth the extra expense? Here are 10 questions to consider when deciding to go diesel.

1. How does a diesel work?

A diesel (which was invented by Rudolf Diesel) is technically called a compression ignition engine. Unlike a conventional gasoline-fueled engine that relies on a spark from a sparkplug to light the fuel, a diesel uses high compression to cause the mixture to spontaneously combust.

2. Are diesel engines are built to last a long time?

Consider all the industries that rely upon diesel engines to handle work in this country. Every semi-truck on the road today has a diesel. And cargo ships typically have a pair (or more) of giant diesel engines turning the props. Diesel engines are under the hood of almost every vehicle used on a construction job site. They are ubiquitous in environments where work must get done reliably—day after day.

John Barta is the assistant chief engineer for GM’s 3.0L Duramax diesel engine. He says heavy-duty pickups have longer life targets than their light-duty brethren. “If you’re buying a heavy-duty pickup, then yes, we have certain designs for longer life,” says Barta. “And we always validate to the worst-case user.”

So, why do diesel engines last so long?

The internal combustion pressures are much higher than gas engines, so those components all have to be more robust. Barta says that internal stoutness is proven because they’ve seen trucks with 500,000 miles on their odometers.

Dave Harriton is the President of American Expedition Vehicles (AEV). They are a premier builder of parts and complete vehicles for off-road expeditions. The company works with many different diesel applications. “The Ram’s Cummins diesel was originally designed as an industrial engine,” says Harriton. “I believe their target goal is 350,000 miles before the first rebuild.” He mentions that in general, their company has found diesels do last longer than gas engines. But the reliability of a diesel can depend somewhat upon exactly how it’s used. More on that later.

3. Why are diesel trucks so expensive?

Check the diesel option box on any heavy-duty full-size pickup truck and it will add roughly $10,000 to the price tag. Yes, that number usually includes an upgraded automatic transmission too, but that’s still a lot of money for an engine option.

“They are absolutely more expensive,” says Barta. “But you get what you pay for. There’s a lot of value in that initial cost.” The components that go into manufacturing a diesel truck engine are inherently more expensive. The stronger components mentioned earlier are costlier to build.

4. Is durability the only reason diesels cost more?

No, there are additional costs in systems that deliver the fuel to the engine and clean up the diesel exhaust.  Barta says fuel injection adds more cost because it must support higher pressures and inject fuel more precisely. And every one of them has at least one turbocharger, which Barta says can add upwards of $1,000 to $2,000 to the cost of a diesel.

On the other end, complicated emissions systems to reduce both particulates (soot) and nitrogen oxide (NOx) can really add to the price of these engines. This requires additional components that go beyond a gas vehicle’s catalytic converter.

Most diesel engines employ a Selective Catalyst Reduction system that injects urea through a catalyst and into the exhaust stream to control NOx emissions. The engine draws this blue DEF (Diesel Exhaust Fluid)  from an additional tank. A diesel particulate filter (DPF) then traps the particulates in the exhaust.

In addition to the parts mentioned above, the emission system requires additional sensors (at upwards of $100 a pop according to Barta) and electronic controllers. All these systems are a considerable engineering cost to the manufacturer, which gets passed down to the diesel buyer. But taking the plunge into diesel brings many benefits, especially when it comes to towing.

5. Can diesel trucks tow heavier loads?

The jump in capability from a gas- to a diesel-engine truck, particularly in the heavy-duty segment, is enormous. A regular-cab, 2-wheel-drive Ford F-350 with the 7.3-liter gas V8 can handle a 22,800-pound fifth-wheel/gooseneck trailer. The very same truck, when equipped with a Power Stroke diesel can tow 35,750 pounds. That’s a big difference. And the numbers are consistently higher across every manufacturer’s heavy-duty pickups.

Light-duty diesel trucks can generally handle heavier loads, too, but the capability gaps are much tighter. For instance, a Chevy Colorado with a 3.6-liter V6 can tow 7,000 pounds. The diesel version can move just 700 pounds more.

Why can diesels tow more?

Low-speed torque. A turbodiesel engine is adept at developing a huge plateau of torque that peaks way down low in the rev range. A high-output Cummins diesel in a Ram 3500 develops 1,075 lb-ft of torque at 1,800 rpm. The heavy-duty Ram’s standard gas V8 produces 429 lb-ft of torque up at 4,000 rpm. So, when towing a heavy load, the gas engine needs to rev higher to make less than half the torque. Because a diesel’s torque hits so soon, the towing experience is more relaxing for the driver and lowers stress on the engine itself.

Turbocharging a diesel has another benefit. When you climb in elevation, a normally aspirated engine will lose 3 percent of its power for every 1,000 feet. A turbocharged engine doesn’t experience that power loss because it automatically compensates for the thinner air, pumping more into the mixture.

6. Do diesel trucks have higher resale values?

One disadvantage to diesel trucks is the high upfront cost for the powertrain. But rest assured, at least some of that investment will be recuperated when you sell the truck. “Heavy-duty diesels—they hold their residual value better,” says Barta. “Customers really value that power and that additional towing capability and they’re willing to pay for it.” According to Kelley Blue Book valuations, diesel trucks are consistently worth more than gas in the used market.

Data for May 2021 shows that a 2016 Ram 3500 diesel has a value that’s 17 percent higher than gas with the same trim level and options. The price for equivalent models of the 2018 Ford F-250 is 10 percent higher for the diesel. Light-duty trucks carry less of a premium. The prices for a 2016 Chevy Colorado diesel are just 5 percent higher than gas. And those for a 2018 Ram 1500 diesel are only 2 percent higher. So, depending upon the model, the investment in diesel could be worth the expense when it comes time to sell.

7. Do diesel engines deliver better mpg?

Diesel engines are around 15 percent more efficient than gas engines, and fuel economy improves by about the same amount. Though the EPA doesn’t provide ratings for heavy-duty pickup trucks, we’ve experienced this in our testing.  On a recent 300-mile mixed driving route in a gas F-350 Crew Cab 4X4, we saw 13.6 mpg.

We tested a Power Stroke diesel version of nearly the same truck optioned the same way and saw 16.4 mpg over the exact same route. We did a similar 300-mile test with two Chevy Colorado Z71 trucks: The V6 Colorado delivered 20.7 mpg and the four-cylinder diesel truck returned 26.7 mpg. So, it’s clear that diesels do provide an improvement in fuel economy. Keep in mind, though, that diesel fuel costs on average about 15 to 20 cents per gallon more than gasoline.

Good fuel economy translates into an extended range. “For our customers, they’re not so much looking at the fuel economy as they are the range. At 80 mph, riding on 37-inch tires, a diesel Gladiator with 4.56 gears can see 20 mpg— that’s pretty fantastic and nearly 370 miles on a tank,” says Harriton. “If you slow it down to 70-mph freeway speeds, it’s more like 450 miles.” But here’s the thing: diesel engines are more efficient when working with a load too. “You’re going to see a reduction in fuel economy when a diesel truck is loaded but it’s more, percentage-wise, with the gas truck,” says Harriton. “The gas truck has to work harder at a higher rpm to move the same load.”

8. Are diesel engines expensive to maintain?

Diesel engines have many advantages, but maintenance costs are not one of them. As mentioned earlier, diesel engines have more complex and expensive intake and exhaust systems than their gas counterparts. And that DEF tank, which typically holds five gallons,  needs to be refilled, sometimes (but not always) in concert with oil changes. DEF costs about $3 per gallon. Barta says, “If you’re towing a lot, you’re going to be using more DEF, so that cost will go up.”

A Ram’s Cummins diesel has two fuel filters. Plus, they take 3 gallons of oil versus 7 quarts in a V8 Ram. Harriton says, “Frankly, it’s a little more difficult to find a service technician with the right expertise to service them. The knowledge base on the most modern diesels doesn’t seem to be there.” Alternators, batteries, starters, and water pumps can all cost more on a diesel. Tire wear is less on a gas truck too. Consider that a Cummins diesel engine weighing in at 1,100 pounds is about double that of a gas V8. So, Harriton says diesels will typically wear out tires more quickly than gas trucks.

9. Is it smart to consider buying a used diesel truck?

Check the specs on new diesel pickup trucks, and it’s clear these machines can move mammoth loads. The good news? Slightly older trucks are nearly as capable. So, by comparing specs and examining how the truck was used, you can find a great used diesel truck for much less than a new one. Diesel engines are made with stout components and tend to last longer, which makes them a smart used-truck buy. Even trucks with close to 100,000 miles on them will have plenty of life left.

While it’s tempting to look for one with low miles, there’s a downside to less rather than more miles. Harriton says you don’t want a truck that’s parked most of the time and used three times a year to tow. Diesels that sit for long periods can have an increased likelihood of condensation in the fuel system, which could ruin injectors. And that’s especially true for trucks that live in humid climates. So, if you’re looking at one with suspiciously low miles, be sure to ask for maintenance records.

10. Should I avoid diesel, and buy a gas truck?

Before deciding to plunk down that hefty premium for a diesel engine, make sure you just don’t want a diesel, but rather that you need one. “If I’m going to be towing a lot and driving a lot of miles,” says Barta, “it makes sense to go with the diesel.” On the flip side, if your daily drives are short and you only tow occasionally, then a gas alternative might be better. That engine is always cheaper, easier to maintain, and gives you quicker throttle response.

While diesel torque feels great and is critical to pulling loads, generally these powerplants feel a bit lazier in everyday driving. While some may be more responsive than others, test drive several models to determine which truck and engine combination is right for you.

4 Great Used Heavy Duty Trucks Under $15,000

FAQ

How often do you change oil in a diesel truck?

Just like vehicles with gasoline engines, diesels should have their engine oil changed every 7,500 miles according to manufacturer recommendations. That interval can extend out to as long as 10,000 miles or could be shorter depending on the use of the truck. If you do a lot of towing in high heat and dusty conditions, a shorter interval is probably a good idea.

What happens if you put gas in a diesel truck?

Gasoline is a lot more volatile than diesel and once it mixes with the fuel, it can cause major damage to your engine. Fuel pumps are equipped with nozzles for diesel that are different in size from gas and are colored green. If you accidentally put gasoline in your tank, have it immediately serviced to drain the fuel and clean out the injection system to avoid severe damage.

Can I jump-start a diesel engine?

Yes, but it will take more power than a gasoline engine to start. Since diesels have a much higher compression ratio than a gasoline engine, they are harder to turn over. So additional power may be needed to energize the starter motor on a diesel engine.

Can I use off-road diesel in my truck?

Diesel fuel used for non-road going vehicles like construction and farm equipment is similar to the diesel used for on-road applications. However, it is not subject to road taxes and is cheaper. But it’s dyed red to indicate its intended use. If you’re caught using off-road diesel, fines are generally $1,000 per incident and $10 per gallon of fuel.

Ben Stewart
Ben Stewart
Ben Stewart is an author specializing in automotive testing and technology. He has a unique perspective—as a lifelong 4WD enthusiast Ben has driven just about every production 4X4 on road and off for the last 20 years. But his expertise and experience goes deeper. Ben has had the opportunity to drive and report on a wide variety of vehicles ranging from pre-production fuel cell cars to... Read More about Ben Stewart

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