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Diesel Questions Asked and Answered

You’ve Got Questions, We’ve Got Answers

Bruce W. Smith
Nov 13, 2018
Photographers: Bruce W. Smith

Oil Change Intervals

QUESTION: I just picked up a ’17 Ram 3500 with the 6.7L Cummins engine. What’s your recommendation on oil change intervals? It’ll be used mostly for towing landscaping equipment or a live-in horse trailer. I used to change the oil every 3,000 miles in my old 5.9L ’01 Ram 3500.
Roland Simmons
via email
Photo 2/5   |   Oil-change intervals vary greatly based on the way a vehicle is used. Some trucks may need oil changed every 3,500 miles, while others can be driven 8,000 miles before service is necessary. For a newer vehicle, the best way to determine how frequently oil should be changed is to have a few oil analyses performed after each of the first oil changes. A good laboratory can tell you the “health” of the oil and whether or not it needs to be changed more or less frequently.
ANSWER: Newer diesels have systems in place to let the owner know what the oil-life percentage is or how many miles are remaining before a reminder/warning flashes in the Driver Information Center, indicating it’s time for oil service. But the alerts are initiated by a computer algorithm that compares everything from idle time and throttle use to vehicle speed and engine temperatures. They are not based on actual internal engine-oil sampling or analysis. In the Ram owner’s manual, it clearly states oil changes “should never exceed 8,000 miles, 12 months, or 350 hours of engine run time, whichever comes first.” It also states if the vehicle is used in “a dusty and off-road environment or is operated predominantly at idle, or only very low engine rpm” the oil should be changed every 4,000 miles. Towing heavy trailers is also considered “severe duty” use, so more frequent oil changes are prudent. We always like to err on the side of being overly cautious when it comes to the lifeblood of a diesel engine. Take the extra step to send in oil samples to a good lab after the second oil change, then do that for the next three to four oil changes so they can tell you more specifically if you needed to shorten that interval or extend it based on what the lab tests show. We believe such tests are a better indicator of when oil should be changed than the computer algorithms that trigger the in-vehicle reminder/warning. If the lab tests indicate you can extend oil-change cycles another 1,000 or 2,000 miles, that will save you some money—even considering the cost of the lab tests. Blackstone Labs, Herguth Laboratories, Schaeffer Oil, O-Reilly Auto Parts, Amsoil, Lubricheck, and others offer oil-analysis services. Some even provide free oil-sample test kits with prepaid mailing. The cost of an oil change and of oil analysis tests over the life of your new truck is a drop in the bucket compared to the cost of rebuilding or replacing an engine that fails due to improper maintenance.

Cold-Weather Additive

QUESTION: Winter 2018 will be the first time I use my ’14 Ford F-250 in sub-freezing temperatures since purchasing it new in 2014. Do you recommend diesel-fuel additives? If so, which one is best and how often should I use it?
Mark Egan
via email
Photo 3/5   |   Winter is a good time to start using a good fuel additive with cetane boost at every fill-up. Using quality additives will result in improved fuel burn, better economy, and more power, and they also help prevent water collection and gelling of fuel in subfreezing conditions.
ANSWER: Yes, it’s prudent to use a fuel additive, because it improves overall performance and is extra preventive maintenance for the entire injection system. Treating every tank of fuel during the winter is also highly recommended, following the instructions on the container. Additives that feature a cetane booster are also good. Alec Hembury at Industrial Injection Diesel Performance recommends all diesel owners use fuel additives. “It adds lubricity to the fuel system that low-sulfur fuel takes away. That added lubricity increases fuel-system components’ life from 15 to 50 percent, and it improves reliability as well as performance since injection-system components can operate smoother. Adding cetane to fuel helps it burn hotter, which increases power and fuel mileage. In addition to increasing lubricity and cetane, Industrial’s Deuce Juice diesel-fuel additive cleans the fuel system and disperses any water in the system,”Alec says. Mark Gotchall at Oregon Fuel Injection says, “We recommend our customers use Stanadyne Performance Formula. Diesel quality varies from area to area across the U.S., so using a good additive with ‘cetane boost’ results in better fuel burn, less smoke, and more power. With a DPF-equipped vehicle, less smoke (even invisible smoke) means fewer particulates are being emitted. That equates to fewer regeneration cycles and better mileage.” Diesel fuel additives also help prevent fuel from gelling when temperature drops below freezing.

Fuel Economy

QUESTION: What fuel mileage should my truck be getting? It’s a ’17 Chevrolet Silverado 2500HD. The truck has 4.10 gears and close to 20,000 miles. Most of that was accrued by towing gooseneck horse or RV trailers, each weighing around 10,000 pounds loaded. The truck averages around 12 mpg while towing and 18 mpg when empty. There aren’t a lot of big elevation changes in the states through which I travel. Other owners I’ve spoken with say their trucks average 20 to 22 mpg empty and 15 mpg towing similar trailers. Is there something wrong with my truck?
Rick Pratt
via the Internet
ANSWER: Unfortunately, many owners perceive a new truck’s “instant-mpg” information as its “average” fuel economy. The truth is, your numbers are right in line with the results we’ve recorded in hood-to-hood comparisons of the Big Three automakers’ ¾-ton four-wheel-drive diesel rigs and comparisons performed under controlled conditions by other automotive journalists. In such tests, the mpg for the 6.6L Duramax engine—as well as the 6.7L powerplants of Ford and Ram—is between 12 to 13 mpg towing trailers that weigh approximately 10,000 pounds and 18 to 19 mpg unladen. The only way to get a handle on your truck’s actual fuel economy involves keeping very accurate fuel-usage records over the course of a year, then dividing total gallons consumed by total mileage driven. The result is the “average” mpg. Separating the fuel used and miles driven according to either towing or non-towing driving conditions will give you a good idea of the average mpg for each of those situations. The important thing to understand about fuel economy is the fact that there are many variables that affect mileage results. Accuracy of the pump(s) used to fill the tank, road and weather conditions, type of terrain, tire inflation, vehicle modifications, and the driving style of the person behind the wheel all have a direct effect on mpg numbers. Drivers who always operate a truck as if there’s a raw egg under their right foot and use the brakes like a fragile load is in the bed will get much better fuel numbers than more aggressive drivers. Terrain and weather make a difference, too. In general, diesels, like all engines, get better fuel economy when it’s cold and dry than when it’s hot and humid. Vehicle aerodynamics, gearing, and speed also play a significant role in mpg. While cruising along a flat section of highway without a trailer at 65 mph newer trucks can yield 20-plus mpg. But speed up to 70 mph and economy drops by 2 to 3 mpg. Engine rpm at a given highway speed also makes a difference, so 3.55 gears will typically get 1 to 2 additional mpg than the same truck will with 4.10 axle ratios. The aerodynamics of the trailer being towed has a big effect on mpg, and, combined with vehicle speed and engine rpm, will also change towing mpg. Don’t worry about the fuel-economy claims of others, and keep an accurate log of your own rig’s fuel consumption (from year to year). If at some point you see a 10 to 20 percent drop in towing or highway fuel economy, that may warrant further investigation.

P11A9 Mystery Code

QUESTION: Diagnostic trouble code “P11A9” randomly appears while driving my ’15 GMC Sierra 3500HD, and I can’t figure out what it’s related to or how to fix it. My hand scanner says it’s “HO2S Performance Signal Low During Moderate Load.” Nothing feels wrong with how the truck runs, so the code that keeps showing up is very puzzling.
Robert Ortega
via email
ANSWER: According to friends at Oregon Fuel Injection, this trouble code relates to two sensors an ECM relies on to monitor nitrogen oxide (NOx) in the exhaust and the subsequent aftertreatment with diesel exhaust fluid. The first of the two “smart sensors” (B195) is located at the outlet of the turbocharger. Its companion is located between the selective catalytic reduction (SCR) and the diesel particulate filter to monitor NOx levels downstream of the SCR. The second NOx sensor also provides the ECM with information on the exhaust’s oxygen level during DPF regeneration. If the upstream sensor on the turbo side is plugged with soot or either of the two sensors are faulty or have loose connections, the ECM will trigger the P11A9 code and the scanner will identify it as an issue with the HO2S (Heater Oxygen Sensor Control). That code is also initiated by any intake or exhaust-system leaks or a faulty EGT sensor. Check to make sure all the intake and exhaust connections and attaching hardware are tight and the air-intake tube isn’t cracked or damaged. If you installed an aftermarket cold-air intake, make sure the sensors fit tightly in the new tube. Loose fitment can cause intermittent P11A9 error codes to occur. If connections are tight, you will most likely need to replace the two NOx sensors.

Dual Alternators

QUESTION: I'm making up a “must-have” checklist for a ’19 Ram 2500. I saw an option for dual 220-amp alternators in place of the stock 180- or heavy-duty 220-amp versions. Are dual alternators worthwhile options? I use my truck for all types of work and outdoor recreation, from hunting to RVing. Are there any downsides? I ask because none of the ’18 Rams my local dealer has on the lot are equipped with that option.
Rusty Wilcox
via email
ANSWER: Ram Trucks offers the heavy-duty dual alternators under the XF7 order code, which adds $395 to the purchase price. That cost is about half of what you will pay to have a second alternator installed—or upgrading to a single with anywhere close to the 440-amp output of the dual system. Is it worth it? Yes, especially when the truck is used for both work and recreation. The factory option places the second 220-amp alternator on the driver side of the 6.7L Cummins engine. That takes away some “working space” when doing maintenance but really shouldn’t be that much of a worry. Dual alternators also require a longer serpentine belt. Belts rarely fail unless some other component does. Still, should you need a new belt, it might not be readily available. Again, not a big deal, especially if you keep a spare in the truck. We think dual alternators on these trucks are a great upgrade for the price. They provide regulated power output that can handle the amp drain imposed by using a heavyweight (15,000 to 16,500 pounds) winch, which typically draws about 400 to 500 amps at full pull, depending on the type of motor being used. Having up to 440 amps available also makes it nice if you want to install a high-output power inverter to run A/C power tools, appliances, and equipment. Dual alternators are a must for anyone planning on using their truck as a snowplow, because operating the plow—and powering warning and other lights—can be just as demanding on batteries as using a winch nonstop. Having that option also bodes well when it comes time to sell the truck, as it widens the range of potential buyers. Will a dual-alternator setup speed up battery charging in the truck or in a trailer? No. Battery charging is regulated by the truck’s computer system and the internal voltage regulator of the alternator(s) to prevent overcharging batteries. A 440-amp system will not charge the batteries any faster than a 180-amp alternator. What the 440s will do is keep pace with a much higher amp draw than the stock alternator instead of depleting the batteries.

LB7 Cold-Start Issue

QUESTION: My ’05 GMC Sierra 2500HD has become increasingly difficult to start since the cold weather arrived, and she’s a bit sluggish when I put the power down. I just replaced five-year-old batteries, but that doesn’t seem to help the starting issue. I also had the injectors and glow plugs replaced. I haven’t seen any error readings come up, either.
Cliff Nadine
via the Internet
ANSWER: When was the last time you replaced the fuel filter? Partially clogged fuel filters are notorious for causing cold-weather hard-starts. It’s also prudent to use a good fuel treatment such as Power Service Diesel Kleen, which prevents gelling while keeping the injection system properly lubricated and cleaned. If replacing the fuel filter doesn’t cure the problem, have a diesel shop perform a full ECM scan and check fuel-rail pressures.

Fast-Idle Kit

QUESTION: Is there a kit available that will give my ’16 Ram 2500’s 6.7L Cummins engine a fast idle? I want it to idle faster during the hot summer to allow the A/C to cool quicker at start-up and so the transmission and engine don’t take so long to warm up in the dead of winter.
Josh Hill
via Facebook
ANSWER: There’s no kit needed if your Ram has cruise control. Fast idle is standard equipment on the 6.7L Cummins engine. Ram says the idle-up feature “manually increases the engine’s idle speed to improve cabin warm up/cool down, increase alternator output, provide increased speed to power an aftermarket-installed belt or PTO-driven device, or other customer need for higher-than-idle speed rpm.” Higher idle speed is also nice when you are charging another vehicle’s dead battery or using the winch. The truck must be stationary, with the automatic transmission in Park or the manual transmission in Neutral with the parking brake set. After starting the engine, tap the cruise control “On” button so the indicator light on the dash shows it’s active. Then press the “Set” button. Your truck’s idle speed should now jump to around 900 rpm instead of its normal 600 to 700. If you want more idle speed, tap the “+” on cruise control or “-“ if you want less. Once the emergency brake is released, the transmission is put into gear, or the “Cancel” or On/Off switch for the cruise control is pushed, the up-idle is disengaged. Higher-idle rpm in subfreezing temperatures helps accelerate transmission warmup, and it also greatly reduces soot buildup during cold-start warmups, which is what contributes heavily to clogging the EGR system. GM owners can do the same if their trucks are equipped with the Fast Idle option (RPO UF3), which applies to Duramax LML, LMM, LWN, and LP5 engines. If your cruise-control-equipped rig didn’t come with the option, any GM dealer can install it according to GM UI Bulletin #85B (Feb.13, 2017), which states: “Adding the Fast Idle (UF3) feature is accomplished by reprogramming the Vehicle’s Body Control Module (BCM). GM Dealers can acquire a new Vehicle Configuration Index (VCI) by contacting Techline Customer Support Center (TCSC). A support-center consultant will create the new VCI with UF3 option as part of the vehicle option content. Note: TCSC typically imposes an administrative fee on the dealers requesting the updated VCI, and this fee may be passed onto the customer. This fee is in addition to the labor charges for the reprogramming of the vehicle. The newly created VCI is readily available for use in the reprogramming of the vehicle’s BCM. Dealers simply need to perform a programming event on the BCM to add the feature/option.”

No Throttle Response

QUESTION: I have an ’00 Dodge Ram 2500 that occasionally experiences a “dead” throttle once the transmission shifts into Overdrive, and the gearbox momentarily downshifts for no apparent reason. The no-throttle issue seems to be getting more frequent. There aren’t any trouble codes, so I’m at a loss regarding where to start tracking down the problem. Any help?
Wes Rankin
via email
ANSWER: The symptom you describe can be caused by several things. Usually, a scan tool will show a P0122, P0123, 222, or 223 diagnostic trouble code, which is related to a defective throttle-position sensor. On rare occasions, as in your case, the sensor will fail without triggering a code. Replacing the TPS, which costs around $200, usually cures the problem(s). The issue could also be related to bad or weak batteries, or batteries with low voltage because of grid heaters coming on. But the voltage issue usually launches MAP and TPS codes accompanied by the dead-pedal situation. If the new TPS doesn’t fix the problem, do a thorough check of the batteries and charging system. We also suggest you have a shop use its diagnostic tools to evaluate your truck.

Replacement Coils

QUESTION: I’m working on upgrading the front suspension on my ’03 Dodge Ram 2500. The truck is set up with Bilstein 5100 shocks and a 2.5-inch leveling kit. I use it to plow roads in the winter and for hunting and fishing during the summer. Last fall, I invested in new heavy-duty rear springs, a Redhead steering box, and a steering-box brace. Now the front sags when the plow is on, and the shocks are almost worn out. There are a lot of replacement coil springs and high-performance shocks offered. Would it be worth the extra money to install Carli Suspension's or Thuren Fabrication's hardware instead of basic replacement coils? What about going the extra mile with shocks from either company?
via the Internet
Photo 4/5   |   Older Dodge Rams that have sagging front coil springs will benefit from upgrading to linear-rate replacements, accompanied by performance-type shocks.
ANSWER: Yes, there are tons of options, from factory to custom, when it comes to replacing coils and shocks. As you mentioned, Carli Suspension and Thuren Suspension Technology offer replacement front coils for Dodge Ram trucks. Both are well known for their advanced engineering and the quality of their suspension products, and either company’s parts are worth the extra investment compared to some of the cheaper “stock-replacement” offerings sold on eBay. It all boils down to the amount or money you want to invest in your truck and how long you intend to keep it. Ride quality with performance-based springs and shocks will be better than stock, even when snowplowing and occasionally using the truck off-pavement. Thuren says this about the company’s Dodge Ram front coils, which makes sense for your specific application in which there’s a lot of extra weight added when a plow is attached: “While multi-rate coils have their place and can provide excellent performance in the right applications, there is simply not enough up-travel from ride height on the heavy-duty Dodge Ram platform before the coil progresses into the higher spring rate to work properly. Once the coil has gotten into the higher spring rate, not only does the compression force rise, but so does the rebound force, and this can lead to a harsh ride compared to a linear-rate coil.” We recommend you ditch the spacers and stock coil springs for Thuren’s 3.125-inch-lift softride coils. You can also add Thuren’s shocks to replace the worn-out dampers. Of course, you might want to shop around and make further comparisons, as there are plenty of other spring and shock brands from which to choose.

Extended Warranties

QUESTION: This isn’t actually a technical question, per se, but one I hope you can weigh in on. What are your thoughts on extended warranties? I’m shopping for a used diesel pickup that’s five to six years old. Several of the used-car dealers I’ve frequented are pushing their extended auto warranty because diesels are so expensive to repair.
Chuck Blum
via the Internet
Photo 5/5   |   “Extended warranties” offered by third-party providers may sound appealing, but the caveats in the fine print can make them ineffective for diesel-truck owners. Study such contracts closely, especially when buying a used pickup, and talk with local repair shops before laying out the money for the high premiums.
ANSWER: Read the fine print very carefully on any third-party (aftermarket) warranty and focus on what’s important when it comes to diesels. First of all, such warranties are actually insurance policies for a specific period of time and miles offered by an outside provider. They also tend to have a lot of caveats and strict limitations related to repairs and reimbursement, which a diesel owner needs to explore thoroughly. The fuel-injection system and transmission are typical big-ticket diesel repairs. Stay away from “bumper-to-bumper” plans on a used truck that’s already beyond the timeframe of the manufacturer’s warranty. The reason to closely read every detail of any extended warranty/service contract is to see exactly how it breaks down the replacement of parts, such as the injection pump, lift pump, injectors, oil pump, and other components critical to the engine’s operation. What does the fine print say about “preexisting conditions” or “lack of proper maintenance”? Is the warranty voided if modifications are made to the vehicle? How many miles/years does the warranty provide coverage? Does the mileage coverage begin from the date you buy the service contract, or is it based on the truck’s existing mileage? Is the “normal wear and tear” clause left to the discretion of the shop doing the work or does a representative of the warranty provider make that determination? How big is the deductible? Is that deductible for the repair job as a whole or each part as a separate repair (say the oil cooler takes out the EGR cooler, which in turn results in a blown head gasket)? Does the failure of one part negate coverage of other associated parts that are subsequently damaged? Do you have to pay for the repairs up front and then wait for reimbursement? If so, how long does it take to get your money back? Can the repair work be provided by any shop or do the repairs have to be made by an Automotive Service Excellence–certified technician? Have you talked to your local diesel repair shops to see what their experience is with such a warranty policy? Is the policy transferable? If you decide to take out such an insurance policy for a new or used truck, keep very detailed records of the vehicle’s maintenance, including all paperwork. Any excuse where the blame for the parts failure can be attributed to not maintaining the vehicle per the manufacturer’s guidelines (“driver abuse” or “normal wear and tear”) can be used as a way not to pay out. The companies that provide extended warranties are in business to make money. They are betting the cost of the policy you purchase will be more than the cost of any repairs it covers during that period. You might consider setting aside what would be the equivalent monthly payments for such coverage each month as your “rainy day fund” to cover unexpected repairs. Doing so could save you literally thousands of dollars over the period of the extended warranty policy. If you feel you must have an extended warranty on a new truck, get it through the OEM if at all possible—not a third-party provider.