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

May 2019

Fuel Mileage and Engine Cooling

June 2019

Ford DPF Cleaning

July 2019

Replacing Head Studs and Fuel Filters

August 2019

Horsepower and Torque Limits

September 2019

Hard -Starting Cummins

October 2019

Oil Temperature and Change Intervals

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. I have a 2001 Chevy 2500HD with Duramax and currently have 105,000 miles. I have done oil changes and lubrication, plus three transmission services during that mileage period. I have not had to replace any engine parts, other than a water pump and serpentine belts in the 16 years I’ve owned this rig (purchased used from a rental agency in 2003 with 12,000 miles). What engine-related issues should I have addressed to continue this pattern of use; i.e., less than 10,000 miles per year?

    • Bruce W. Smith replies: The LB7 Duramax (2001-2004) is a good engine, and treated as you do, it’ll prove reliable for a long time. But like all diesels, the LB7s have their own little array of mechanical issues and concerns that have cropped up over the years. Unfortunately, one to prepare for sooner than later is replacing the injectors. The original OEM injectors are prone to cracking between 80,000 and 125,000 miles, which is right around the mileage your truck has reached. This results in a smoke haze at idle, an increasing loss in fuel economy and diesel getting into the engine oil, increasing the volume in the oil pan. The only fix is having all the injectors replaced with aftermarket ones, along with new glow plugs and high-pressure injection lines that feed the injectors.

      The latter are prone to corrosion and restricted flow, which also leads to poor fuel economy, loss of power and, of course, fuel leaks at the injectors. Always replace the injector lines when replacing the LB7 injectors. You can find complete kits to do this for less than $2,000. It’s a labor-intensive job, so if you aren’t doing this yourself, be prepared for the added costs. The glow plugs can be a problem removing because they tend to seize in the aluminum heads. Along those same lines, so to speak, the LB7 fuel lines from the tank are known to rust out, air leaks develop because of loose fuel-line fittings, and O-rings leak at the fuel-filter housing.

      While the injectors and glow plugs are being replaced, it’s a good idea to have the heads pulled and the head gaskets replaced. A lot of these engines experience head-gasket failure in the 100,000- to 150,000-mile range. This can be easily checked by squeezing the top radiator hose after the engine has been warmed up and then shut off. If the radiator hose is hard, the head gaskets are problematic. Leaking water pumps, as you already know, were also a common replacement item on the LB7s.

  6. What is the main cause of a 2003 Dodge Ram Cummins with 150,000 miles that starts really well in warm weather or with the heater plugged in but is very hard to start in cool or cold weather? The engine cranks well, and no codes show up when checked, with the ignition switch on and off using the “three-times” method.

  7. I have a 2006 Siveraldo Duramax pickup. The stock fuel filter has a water-detection device that has never produced a warning in the 155,000-plus miles on the vehicle. I have been told the Cat 1R-0750 filter is a better filter, but it does not have a connection for the water detection. Should I be concerned about this? Does the Cat filter trap any water in the bottom of the filter, even though there is no way of sending a warning to the instrument panel?

    • Bruce W. Smith replies: The reason you’ve never seen a warning is because there’s never been enough water in the fuel to trip the sensor. Be thankful for that. It’s my opinion that it’s best to use only the GM fuel/water filter or a direct replacement such as the Racor Coalescer Fuel Filter (PFF50216) on any of the 2001-2016 Duramaxes. It takes only one hit of water-contaminated diesel to result in a very costly Duramax repair job. (The high-pressure injection pump and injectors really don’t like water.) That Water-in-Fuel (WIF) sensor in those filters at least gives the driver a heads-up that there’s an issue, and the engine needs to be shut down immediately.

      The step design of both the GM and Racor fuel/water-separator filter provides a little additional space for water to get trapped before it can head toward the high-pressure injection pump and on to the injectors. When you do replace the filter, don’t overtighten the WIF when you put it back on the new filter. GM techs say to tighten it finger-tight plus a quarter turn. Overtightening the sensor will surely crack it. This will cause air to get into the fuel system as the injection pump is pulling the fuel from the tank, and when that happens the engine will either not start or start then die. I also suggest stretching the largest O-ring a couple times before putting it on the new filter. This seems to make the O-ring fit perfectly when the new filter is installed.

  8. I have a 2006 Chevy HD 6.6-liter Duramax and am considering using the Sinister Diesel CAT fuel-filter conversion kit. But I’m concerned about doing without the OEM water-in-fuel warning and extraction system. YouTube videos laud conversion primarily because of particulate size and less expensive filter but fail to address the water issue. Any guidance would be much appreciated.

    • Bruce W. Smith replies: The water-in-fuel (WIF) sensor on the GM filter is there for a reason — to warn the driver there is water in the fuel. If water gets past the fuel filter, then the injection pump and injectors take a huge and costly hit. RVers are the most likely to get a bad batch of diesel as they travel around the country, sometimes not having a choice as to where they refuel. The secondary CAT filter does a great job filtering small particulates and is less expensive than the OEM filter. But you can buy a lot of those OEM fuel filters for the price it’d cost to replace an injection pump and/or set of injectors, should you get a water-laden batch of diesel along the way.

  9. I have a 2013 Ram 6.7-liter diesel with 54,00 miles on it. The owner’s manual says to replace the two fuel filters every 15,000 miles. That costs $300 at the dealership. Is there any way to extend the interval and stay within the warranty?

  10. My questions concerns my 2005 Dodge Ram tow vehicle. I have the 5.7-liter Cummins diesel engine, and it is beginning to show some disturbing symptoms. I’m having a general power loss, and when I brought it into the mechanic, he replaced the fuel fiter/lift pump with a FASS system. While this helped a bit, I feel that my power loss issue remains. To me it sounds like the turbo is not providing the usual boost based on the lack of the turbo “whine” and the usual g-forces when the turbo kicks in. I’m also seeing an unusual amount of black smoke upon start-up and when accelerating. I have cleaned up the MAF sensor, but that did very little to improve my performance woes. I would very much appreciate if you could help me diagnose and repair my power plant.

    • Bruce W. Smith replies: Black smoke usually means the engine is getting plenty of fuel but not enough air for the fuel being delivered to make a complete burn. Add the “general loss of power,” and the finger points to either an air leak between the turbo, intercooler and intake or a clogged air filter. It’s not unusual for the spring-tension bands on the connection boots between intercooler and intake to work loose, or the boots get a hole in them or split, resulting in a massive air leak.

      An air leak anywhere in the turbo/intercooler/intake loop will result in little or no boost, and black smoke as the result of not enough air flowing into the cylinders for complete combustion. It’s also common on those engines to have the turbo wastegate get stuck because the actuator can’t function properly from excessive carbon and soot buildup. If the actuator has the wastegate stuck in the open position, the turbo can’t build boost (power). The actuator can be replaced, but we’d suggest going to a remanufactured turbo. BD Diesel Performance and Industrial Injection, among others, offer several drop-in turbo options along that line.

  11. 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.

  12. I own a 2006 Chevy 2500HD 2WD extended cab with 130,000 miles on it. I can’t seem to get more than 11.5 to 12 mpg, whether I am towing or not, on hills or flat land. Any suggestions? My other concern is that I can’t keep the truck cool when towing long grades like Oregon’s Siskiyou Pass. I have replaced the radiator and change the transmission fluid every 25,000 miles. I have had the gauges checked for accuracy. The truck is stock. I pull a 33-foot Dutchmen Grand Junction fifth-wheel trailer.

  13. I have a 2005 Dodge Ram dually Cummins that has begun having starting problems when the weather gets below 45 degrees Fahrenheit. It started tripping the Check Engine light, even when the block heater was plugged in overnight. The codes were MAP sensor, IAT sensor and battery-temp sensor. The air-intake heater works fine, and replacement of all sensors was performed. The block heater makes it easier to start, but why is the minimally cold weather here in southern Arizona affecting it starting?

  14. 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?

  15. 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?

  16. I have a 2106 Ford F-250 6.7-liter diesel that we tow a Heartland Big Country fifth-wheel with. On three occasions, only when towing, we suddenly start to lose power and get a warning light saying Drive to Clean. We have to unhook from the trailer and usually drive at highway speeds for 20 to 30 minutes to clear the warnings on the instrument panel. We can then hook back up to the trailer, and everything is fine. The pickup has 76,000 miles, with probably 15,000 of those towing. Any help would be appreciated.

  17. My 2001 Ram 2500 diesel 4×4 Ram Cummins 5.9-liter is a great truck. It has 200,000 miles on it and now takes a long time to get up to speed compared to when it was new. I would like to know how to get more power and if there’s a proven diesel fuel “enhancer” to get more mileage to the gallon. I get 12 mpg or so carrying an 8-foot, 1-ton slide-in camper. I don’t want high-priced additions that might screw up my wonderful truck.

    • Bruce W. Smith replies: There are a number of diesel fuel additives out there that clean and lubricate the injection system. I’d run through three- or four fill-ups treating each tank with Stanadyne Diesel Fuel Additive or Power Service Products Diesel Kleen. If you don’t see a marked difference in both power and fuel economy, it might be time to contact companies such as Sinister Diesel, Banks Power, Industrial Injection or Diesel Power Products to see what they’d recommend in the way of remanufactured injectors and a new, upgraded turbo.

      You don’t mention any injector or turbo changes on your Cummins. Turbos and injectors wear out, losing their efficiency and putting the hurt on power and fuel economy. On those second-gen Cummins, a lot of owners have replaced the stock Holset HX35/HY35 turbo with the Industrial Injection K27 Borg Warner Performance drop-in turbo so they can retain the factory exhaust brake. As for injectors, we’ve heard good results using Bosch RV275s, which are 40-horsepower over stock. They’d work well with the BW turbo. That combination keeps everything still close to “factory” and should be good for another couple hundred K.

  18. When I hooked up my trailer, a 2015 Shasta Revere, to my 2019 Ram 4WD 1500 Crew Cab with the 5.7-liter Hemi eTorque, the bed of the truck sags a lot. The truck has a 6-foot, 4-inch bed. I had my Triumph Street Triple motorcycle (414 pounds) and my Load-All ramp in the bed. I have the 3.92 rear axle and towing package. Even without the motorcycle in it (just the ramp), there is considerable sag when I hook up the trailer. I have to really tighten up the weight-distribution bars, but still there is more sag than I would like. Would you recommend changing coils or some other method to eliminate the sag? I don’t want to increase the carrying capacity, just eliminate the sag.

    • Bruce W. Smith replies: You didn’t mention what model Revere you are trailering, but a 32-foot 27BH, for example, has a dry weight just a few pounds shy of 6,000 pounds and a hitch weight of 604 pounds. Add freshwater, food, clothing and miscellaneous gear, and the weight of the trailer could easily be closer to 7,500 pounds with the hitch weight more than 750 pounds. That’s well below that model Ram’s maximum tow rating of 11,120 pounds and 1,680 pounds max payload rating. But the coil suspension on those tend to squat, as you have noted, without the self-leveling air-suspension option.

      The easiest way to keep the rear from sagging under such a load is to invest in a set of air helper springs, overloads or progressive-rate urethane-type helper springs to supplement the stock springs. SuperSprings offers urethane helper springs, and numerous aftermarket manufacturers offer air-helper spring kits for the Ram 1500s including Air Lift and Firestone Ride-Rite. Which route you take all depends on what level of investment, ride comfort and suspension adjustability works best in your situation. I prefer using air to control ride height over other helper spring options in this instance.

  19. I have a 2005 Ford F-350 DRW 6.0-liter Power Stroke with 110,000 miles. It’s been pretty trouble-free while pulling a 15,000-pound fifth-wheel trailer about 8,000 miles per year. I’ve always heard that the OEM head bolts can be a problem and would be better replaced by ARP studs. My question: Can you replace the head bolts with ARP studs one bolt at a time, carefully torqueing them to spec in a recommended torque pattern?

  20. There are reports that the CP4 fuel-injection pumps are subject to failure. I have 102,000 miles on my 2012 Ford Super Duty and plan on keeping it for another 5 years. Should I consider being proactive and replace my pump now?

    • Here’s Bruce W. Smith’s reply to a similar question from another reader: We would be interested in actual CP4.2 failure numbers, too. But OEM manufacturers of products, especially vehicles, don’t generally disclose failure rates or discuss related warranty-repair information unless prompted by some legal action. A couple of class-action lawsuits were filed in the latter part of 2018 that are related to CP4.2 failures and owners of the affected vehicles seeking monetary compensation.

      Failures of the CP4.2 pump are enough of a perceived issue that aftermarket companies such as S&S Diesel Motorsport have gone to the time and expense to offer modified CP3 replacement pumps or bypass kits when the pump can’t be replaced by a better or more reliable version. Having an aftermarket product go through the CARB-certified, 50-state EPA legal process is a costly endeavor in itself, so these companies wouldn’t be doing this just for grins; they have consumers prompting them for the new products.

      For more on this topic, read Bruce W. Smith’s May 2019 Trailer Life article, “Diesel Heart Transplant,” about swapping out the Duramax engine’s CP4.2 pump for its modified predecessor.

  21. I’m fairly new to diesels. Mine is a 2002 with 150k miles on it. I tow a 10K fifthwheel. What are your recommendations for maintenance, fuel economy and any aftermarket products?

  22. Ted, as with any diesel pickup, clean fuel, lubricants and filters are the keys to extending engine and transmission life. If that truck is used for towing, at the very minimum follow the “Severe Duty” maintenance as noted in the owner’s manual. Personally, I’d change the oil and filter every 3,500-4,500 miles, have the Aillison transmission fluid and filter changed every 25,000 miles, the cooling system flushed every 50,000-75,000 miles (or every three years), and change the fuel filter every third oil change (GM recommends 15K or as indicated in the instrument cluster display). Of course, changing/cleaning the air filter every 25,000 miles or sooner if needed. It should be checked at each oil change. To maximize fuel economy, drive with a very light right foot and keep speeds below 60mph. As for aftermarket parts, it all depends on what your goals are. One of the best add-ons is an Edge Products Insight CTS2 (, which allows you to monitor all the engine functions from exhaust gas temperatures (EGTs) to boost, transmission to oil and coolant temperatures. If you want vehicle monitoring with six levels of switch-on-the-fly horsepower bumps, the Banks EconoMind with iDash 1.8 Monitor is a good choice.

  23. I have a 2016 F-250. What do you recommend to keep me from having engine problems with the Bosch CP4.2? I have been using a fuel-injector cleaner in the fuel for a year now.

    • Bruce W. Smith replies: A lack of lubricity, air in the fuel or contaminants (water, dirt, etc.) in the fuel are the killers of CP4.2 high-pressure fuel-injection pumps. Using a high-end aftermarket lift pump and changing/checking the fuel/water filters on a regular basis are preventions for two of the three factors. Dosing your fuel with an additive that increases the lubricity of the diesel, such as Stanadyne or Diesel Kleen, is the third preventive measure. If you use a diesel fuel lubricity additive, use it in accordance with the manufacturer’s directions. More, or a higher ratio, of an additive isn’t better.

      For more information about lift pumps, see the April 2019 Diesel Tech Q&A.

      For more information on CP4.2 fuel pumps, see “Diesel Heart Transplant.”

  24. I have a 2013 GMC Sierra 2500HD with the 6.6-liter Duramax. At the last oil change, at 72,000 miles, I opted for 15W-40 Mobil synthetic at the advice of the shop. Does synthetic oil last any longer than regular oil in diesels, like they say it does for gasoline engines, or should I follow the Change Oil Soon message? Is synthetic oil a waste on diesels?

  25. I really appreciate the Diesel Tech Q&A addition. I have a question about my 2012 Ford F-350 6.7-liter diesel. There is an oil-temperature gauge, but no one can tell me what the upper limits should be and for how long. I have come up to 230 degrees while towing up a mountain grade, but it quickly drops to the 200- to 210-degree range when the grade levels off. The coolant temp never seems to get above the normal range. I use Shell Rotella T6 full synthetic 5W-40. I use the gauge to let me know when the oil is warm enough to begin towing.

  26. I have a 2015 Ram 1500 EcoDiesel that just turned over 34,000 miles. It has started losing coolant, about an inch in the degas bottle during a 600-mile trip I took last week. The dealer did a pressure check but found nothing. No visible signs of a leak or coolant in the oil. Any suggestions where the coolant could be going?

    • Bruce W. Smith replies: The first thought is it could be an internal exhaust gas recirculation (EGR) cooler leak. If the feed to the EGR valve shows signs of moist, sludgy soot, it’s a leak inside the EGR cooler. But that is rare on a diesel with as little miles as yours. Higher mileage engines see this because of the constant expansion and contraction the EGR cooler cycles through in its normal function cooling hot exhaust gases.

      Also consider that the coolant line to the turbo center section may be leaking. The turbo water feed tube is located under the intake in the valley of the motor and comes from the driver’s-side head. It’s made up of two hard lines that are connected by a rubber heater hose. The feed line uses two banjo fittings (19mm and 22mm) that have been known to loosen and leak. If they were to leak, the coolant would burn off on the hot turbo and exhaust and not show signs of a leak.

      Related to that is the rubber hose that’s part of the line. It’s known to fail with age from the engine/turbo heat. There are also two hard coolant lines that run from behind the water pump and under the intake. Those lines have O-rings to seal them from leaking. When they leak, it is very difficult to notice. The slowly increasing coolant loss could also be a water pump on the way to failure.

      All of the above would require a dealer to check out — or someone with the tools and diesel tech skills. Remember, tracking down leaks, especially coolant-related, can be very difficult. Your dealer will probably use a fluorescent dye poured into the coolant tank to make the source of the leak easier to spot.

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