This 2017 GMC Sierra 3500 Diesel Towed for 22,000 of Its 24,750 Miles: How Has It Held Up? - PickupTrucks.com

Posted by PickupTrucks.com Staff | October 28, 2019

Cars.com photos by Matt Barnes

By Matt Barnes

For my day job, I am a product engineer for Progress Mfg. Inc. in Utah, makers of the Equal-i-zer hitch and Fastway Flash ball mounts. As part of my work, I test various pieces of trailer towing equipment including trailer hitches. One vehicle our team uses for testing is a 2017 GMC Sierra 3500 SLT 4x4 crew-cab long bed with the 6.6-liter turbo-diesel V-8 Duramax (445 horsepower and 910 pounds-feet of torque). In the two years we've had the truck, we logged 24,750 miles, of which approximately 22,000 were driven towing trailers weighing more than 14,000 pounds.

Related: 2017 GMC Sierra 3500 Proves to Be a Serious Hauler

Most of our testing is performed by driving steep and curvy mountain roads. A typical day of testing will see elevations starting at 4,600 feet and topping out at higher than 9,000 feet. Along with that, there's hard acceleration and heavy braking, as well as intentionally driving on rough roads with large bumps and potholes, and even some gravel and dirt roads thrown in the mix.

Repeated Coolant Hose Leak

Even when towing at the truck's maximum rated capabilities, we've never had a failure that stopped the truck from towing its load home, but that doesn't mean it's been problem free. Let's look at the work we've put into it.

Three times in the first 10,000 miles we had a low coolant message appear. The dealership found one of the coolant hoses had become disconnected. The first time it happened, we thought that the clamp may not have been properly set during the initial assembly. The second time the same hose disconnected, however, we started wondering what the real issue was, but the dealer assured us it was fixed. The third time we asked the dealer to put a screw type hose clamp on, rather than replace it with the factory spring style clamp, and this seems to have been the solution because we haven't had a problem since.

Transmission Overheat

With a little more than 6,000 miles on the truck, I was climbing one of the steepest grades in the area in 90-degree F weather and got a message saying: "transmission hot — idle engine." I was pulling a 17,000-pound trailer and the slope had portions that were over a 20 percent grade. If it were a straight road I don't think it would have been a problem, but the curves forced me to keep my speed down, which kept the truck from locking the torque converter. Once I had idled for about 10 minutes, I continued my drive and made it to the summit without another warning. Something to note here is that when a vehicle is displaying an overheating message, don't turn it off unless there is a lack of oil, coolant or transmission fluid. Letting a vehicle idle will allow the cooling system to do its job — removing heat from the engine and transmission. If the vehicle is turned off, the fluid will no longer flow and warping from heat soak could occur.

Braking Anomaly

As we noted in the one-year review, we had an incident where the truck continued to accelerate when the brake was pedal was pushed. I was descending a snowy 6 percent grade in 4WD High with the exhaust brake on. When I braked for an upcoming corner, the truck accelerated. I applied the trailer brakes using the trailer brake controller to slow for the turn. I then reproduced the incident on a straight section of road. Shortly after the incident, a service bulletin was issued for a computer update and we have been unable to replicate the issue since.

Worn Trailer Hitch

At around 20,000 miles, the trailer hitch receiver was so worn that we decided to replace it. The hitch pin hole had elongated significantly, allowing for a lot of play in the hitch. Most consumers likely won't have this issue, as we are extremely hard on our equipment. Rather than getting an upgraded aftermarket unit, the receiver was replaced with a factory unit so that we could continue testing with the setup that most of our customers will likely have.

Two-Year Maintenance: Oil, Diesel Filter, Tires

In the nearly 25,000 miles we've driven, the truck has had four oil and oil filter changes, each of which included a check of all fluids. All of this was covered by the dealer where we purchased the truck or by GMC. We haven't had fluid changes apart from the oil, and the only topping off we had to do was the coolant due to the early leaks.

We replaced the diesel fuel filter on our own at 21,000 miles. The filter cost $23 and took us about 15 minutes to change. During that time, we never had to drain water out of the filter. This is probably more of a testament to where we get our fuel than anything to do with the truck itself.

Our first set of tires made it less than 8,000 miles, and apart from fuel, tires have been our biggest expense for the truck. The second set of tires have more than 16,000 miles on them and still have a significant amount of treadwear left.

Sierra 3500 Diesel Fuel Mileage

Over the past two years, the truck has returned an average of 11.6 mpg, which is down slightly from the 11.8 mpg we reported at the one-year mark. When empty, it's easy for the truck to return more than 20 mpg on the highway. When towing, mpg will vary greatly depending on the load size, weight and shape.

Interior

Inside the truck we have had no issues. The leather is in great condition, all the electronics have worked flawlessly, there have been no problems with the infotainment system, and it has remained very comfortable with no sagging in the seats. This is one area of the truck where we aren't as hard as many others would be. We typically have clean attire and are careful about what we put on the seats.

Find a GMC Sierra 3500 for Sale Near You

Overall, we have been very impressed with this truck. There have been no reliability issues and it has a decent ride with a comfortable cabin and seats, and pulls any load we put behind it with ease. Would we buy this truck again? Absolutely.

2017 GMC Sierra 3500 Overall Ownership Costs:

• Maintenance visits: $0
• Fuel (2,134 gallons): $6,512
• Diesel exhaust fluid (38 gallons): $118
• Coolant (2 gallons): $34
• Fuel filter: $23
• Tires (one set of four): $1,194
• Trailer hitch receiver: $532
• Total: $8,413

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