To complement Trailer Life’s long-running RV Clinic column, we’ve launched an online technical question-and-answer section devoted to diesel tow vehicles.

Topics cover all aspects of diesel vehicles from engines to transmissions, gearing to fuel economy and tires to turbos. Each month Bruce W. Smith responds to one question in depth, and readers’ comments add to the conversation.

January 2019

Diesel Deletes, Good or Bad?

February 2019

Axle-Ratio Selection and Fuel Economy

March 2019

Tow-Rating “Recertification”

April 2019

Lift Pumps

Ask a Question

If you have a question about maintenance, repairs or upgrades to your diesel truck, SUV or van, scroll down to the Leave a Reply box at the bottom of this page. Please include your full name, city and state or province.

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.



  1. I have a 2013 Chevy 2500HD. I’ve heard of people removing the DEF system to get better performance. This seems like a complicated process. I’m assuming this would involve a new CPU chip. What if I needed to take the truck to the dealer for service? Would they still service it? I have 65,000 miles on it, but I would wait until the warranty ended before I did this. Thank you.

  2. I have a 2012 GMC 3500 Duramax. I am being told to have it “deleted” by most everyone. What is your opinion? Advantages and disadvantages?

  3. I have a 2015 Ram 1500 EcoDiesel. I’m curious about burning biodiesel. I’ve read some of the pros and cons, and I’ve read that, initially, this may require a fuel-filter change, as the biodiesel is a solvent and will dislodge some sludge. I’ve gone through that and determined I’m comfortable with the procedure. Generally, I’d like to hear your take on running biodiesel, and, specifically, I’d like to know how quickly that fuel filter will clog up and what that will look like (will I get warnings from the computer, or will it just fail?), and if that will be a frequent issue going forward. What if I’m switching back and forth, as biodiesel is not readily available in many regions?

    • Thanks, Bob. Bruce W. Smith has added your question to his list to consider for future Diesel Tech Q&A posts. In the meantime, he offered this brief reply:

      Prior to 2007, all diesels were B100 (100 percent biodiesel) compatible. After that, the EPA changed the emissions standards on diesels, so they now require at least B15 (15 percent biodiesel) fuel. Today’s diesel engines can run on B20 — but only if that biodiesel meets ASTM D7467-17 standards — which “home-grown” biodiesel probably doesn’t.

      As for fuel-filter plugging, early on that was a problem — more so with those making their own biodiesel than biodiesel sold by large manufacturers. Here’s a good explanation:'s/06-1.pdf

  4. Two questions:

    1) I’m debating between 3.42 and 3.73 axles on the new Ram 3500 diesel dually. I understand fuel mileage will be better with the 3.42, but how much better under similar conditions — e.g., pulling a large fifth-wheel? There are lots of factors besides axle ratios that won’t change (wind and tire-rolling resistance, for instance), so I’m guessing the difference will be less than the 3.73/3.42 ratio would indicate.

    2) With HD pickup manufacturers locked into the horsepower/torque race, I’m guessing they’re primarily retuning the same engines and pushing ever closer to the limits of what the parts will handle. At what point will the drive for more horsepower/torque affect engine longevity? To what extent can reduced longevity be mitigated by taking it easy and not burying the go pedal in the floor?

  5. Can you explain why the 2018 Ram 2500 diesel (6.7L) 4WD has a higher tow rating with the 3.42 gears at 17,160 pounds than it does with the 3.73 gears? When you request the fifth-wheel towing package option, it always defaults to the 3.42 gears only. From what I’ve seen on the 2019 Ram 2500 available information, the tow rating is up to around 19,000 pounds, but it still shows the 3.42 gears and not the 3.73.

    • For this question, we contacted Nick Cappa, communications manager at FCA’s Ram Trucks division. Here’s his reply: “You cannot order a Ram 2500 with diesel and 3.73 gears. Sounds like Buck France is seeing a 6.4 V-8 with 3.73 gears, which would have a lower tow rating.

  6. I am driving a Ram 2500 with a 3.42 axle ratio. I just bought a fifth-wheel that had a pin weight higher than the truck’s load limit. The dealer told me I could replace the coil springs with heavier duty coils and have it recertified, which I did. Did I do the right thing?
    Thomas Paul

  7. I have a 2016 Ram 3500 Crew Cab dually with the 6.7-liter Cummins. It has just over 45,000 miles, most of it towing our 2017 Keystone Cougar 367FLS fiver. Several of my friends who are also full-time RVers say that installing an aftermarket “lift pump” on the Cummins is a good investment. What’s your opinion?


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