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Diesel Tech Questions: You Have Questions-We Have Answers

Top Tech

Bruce W. Smith
Aug 8, 2018
Photographers: Bruce W. Smith

Pyrometer Placement

QUESTION: Why is the pyrometer’s probe placed after the turbocharger on a Class 8 tractor, and in the exhaust manifold (before the turbo) on a pickup? Also, what are the safe operating-temperature limits of both?
Wayne Dillon
via email
Photo 2/7   |   The ideal placement for a pyrometer probe is in the exhaust manifold, where the EGT is the most representative of what’s happening in the combustion chambers. It can be more than 400 degrees cooler where the exhaust exits the turbo.
ANSWER: It’s commonplace for pryometer systems to measure either pre-turbo or post-turbo temperatures. The location of the probe depends on where a truck manufacturer’s engineers feel is best for the application. Their decision takes into account EGT accuracy, along with position for ease of service and cost concerns. They all contribute to the reason for post-turbo pyro placement on Class 8 rigs. The preferred location for getting true EGT with the most accuracy is immediately after the exhaust leaves the cylinder head, so the probe is located in the exhaust manifold or in the inlet to the turbo. Once exhaust hits the turbo, EGT can drop as much as 400 degrees. That temperature reduction can easily contribute to cracked heads, split pistons, or a destroyed turbo if it is not monitored. Pre-turbo EGT on daily driven trucks should be kept at less than1,200 degrees under full load. Exceeding 1,300 degrees (pre-turbo) for any extended period of time is known to cause damage. What’s our suggestion for EGT “redline?” Play it safe: 1,150 degrees (pre-turbo), and 750 degrees (post-turbo).

Blowing Flexplates

QUESTION: I have an ’04 Ford Super Duty that has destroyed three flexplates. When I bought the truck back in 2016, it had 145,000 miles on it, and I just had the engine completely rebuilt to take care of all the problems that plague 6.0L Power Stroke engines. Since then, I’ve added another 20,000 miles, and I have had the transmission out twice in that time to replace the flexplates that have come apart in the center. The second time, I installed a Ford flexplate along with a rebuilt transmission and a new torque covnerter. After just 1,200 miles, that flexplate also came apart. The truck has a 6-inch lift and 38-inch-tall tires. The engine and transmission mounts are new, as are the driveshafts. The only modifications to the engine are SCT ECM tuning and Garrett PowerMax turbocharger. Everything else is stock. What am I missing here?
Jack Conlee
via email
Photo 3/7   |   Flexplate failure is usually the result of damaging vibrations from the crankshaft or driveline, movement between the engine and transmission, or from high torque loads and hard shifts. Stock flexplates should be replaced with billet-style units when failures occur.
ANSWER: There appears to be some movement between the engine and transmission that’s causing the flexplate to flex way too much. In the process of installing the different flexplates, did you notice if the two alignment dowel pins in the back of the block are worn or missing? The dowels are essential for making sure the transmission and engine align and are bolted together properly. If you’re in doubt, install new ones. Going in another direction, if the problem began after the rebuilt engine was installed, it is worthwhile for you to ask the builder if the endplay in the crank was checked before the engine went back into the truck. Kenneth Tripp at Tripp Trucks in North Carolina says Ford 6.0L specifications call for maximum crankshaft endplay of .020 inch (.508 mm). Aden McDonnell at Automatic Transmission Specialists in Livingston, Montana, says he has seen blown flexplates (and cracked transmission cases and engine blocks) caused by harmonics from driveshafts that are at the wrong angle. Aden also says, “Excessive shift pressure, harsh shifts, an incorrectly tuned transmission, or extreme converter lockup can all transfer more energy than the stock flexplate can withstand. Installing a billet flexplate for the 5R110 is a good idea.”

Compound Advice

QUESTION: I own an ’06 Ram 2500 with a few minor mods. The truck has 124,000 miles on it. My wife and I are planning on buying a fifth-wheel RV and doing a lot of traveling. For multiple reasons, I am seriously thinking of adding a second turbocharger to the stock unit. Nothing extreme, just something to help keep EGT down and give it a little more grunt. I will probably also add EFILive tuning. My question is: At what point do I need to worry about replacing head bolts with studs? I don't plan on getting all wild and crazy with it and am on a limited budget. Any advice would be appreciated.
Mike Yates
via email
ANSWER: When properly tuned, compound turbochargers are great for making power while keeping EGT in check. However, there is a better way to do what you want without the expense of setting up the engine to handle the high boost pressures you will experience when towing a fifth-wheel travel trailer. Bill Allen of Source Automotive says, “You can get the same power bang you will with compounds and stock fueling by going with a single-turbo setup. But knowing the average altitudes of areas the truck will primarily be used for towing is vital to selecting the correct turbo. We make these modifications a lot at our shop (in Oregon) for commercial and RV customers. We recommend a High Tech Turbo–prepared 62/65/14 BorgWarner S300 turbo, Mads Smarty Jr. programmer, and a Mishimoto intercooler. That package will drop EGT 300 to 400 degrees, while increasing fuel mpg and improving overall driveability by a ton!” Bill recommends having ARP 2000 cylinder-head studs installed to prevent head-gasket failure due to higher combustion pressures. He also notes that installing an AirDog II 4G DF165, FASS, or similar lift pump air/fuel separation system will take some of the fuel-delivery load off the factory CP3 injection pump and protect the injectors from water inadvertently entering the injection system. With these modifications, you should be able to tow the RV with plenty of power (and safe EGT) for tackling big, long grades.

Sand Driving Tips

QUESTION: I know most of the tech questions you get are related to power, engines, and transmissions, but I was hoping you might be able to give a few tips regarding towing a trailer in sand. I’m a little apprehensive about getting our new 34-foot toy hauler stuck. Our tow package is a stock ’16 Ram 3500 with the 6.7L Cummins.
Jay Hawkins
via email
Photo 4/7   |   Towing in sandy terrain requires airing down trailer and tow-vehicle tires. For example, it’s common for sand-loving ATVers in the Pacific Northwest to lower toy-hauler tires to 15 psi and as little as 12 psi on their diesel tow rigs.
ANSWER: When it comes to driving in the sand, flotation and momentum are your two best allies. Those who love to “sand camp,” as you plan to do, air down their truck and trailer’s tires as low as possible without busting beads off the rims. The low air pressure creates a wider footprint, which gives better flotation in sand (and snow). A good starting point for trailer-tire air pressure when towing in sand is 16 psi, with 15 psi for the rear tires of the truck, and 12 psi for the front, as they are carrying the lightest load. If that’s not low enough, drop another pound or two from the truck’s tires. It’s also prudent to run a tire/wheel combination that provides enough tire sidewall to allow the under-inflated tires to flex without popping off the bead. In this instance, 16-inch trailer rims and 17-inch truck rims are good choices. We also recommend having a good onboard air system to reinflate tires, along with six 4x2x8 wooden boards, and/or four emergency traction mats such as those offered by Maxtrax (ok4wd.com), just in case the tires of the truck, trailer, or both begin to sink. The boards are also invaluable for helping keep the trailer stable on jacks once it’s parked on the sand. We also recommend having a strong winch (minimum 12,000-pound capacity) and heavy-duty winch bumper installed on the tow rig, just in case self-recovery is needed. As for driving tips, there’s really only one: Keep a good amount of forward momentum while driving over soft, dry sand when towing in/out of your camp. When you take off in sand, roll lightly into the throttle until the truck is moving forward, and then be more aggressive. If you feel the tires digging down instead of rolling forward, get off the throttle and use the traction mats or boards instead of burying the tires. With aired-down tires and a little judicious weight on the right foot, you shouldn’t have to worry when towing over relatively flat, sandy terrain.

F-550 Muscle-Up

QUESTION: I haul buildings ranging from 8x10 to 14x40 feet up to 15 feet tall and plan on buying a ’19 F-550. Chassis cabs are detuned approximately 100 hp. I've been told they have smaller turbochargers so you can't just use a programmer on them. Also, I don't in any way want to jeopardize longevity. (This is a hauling truck I use to make my living, on the highway, mountains, dirt-logging roads, you name it—five days a week) So, what is your input? Is there a safe and not too expensive way to at least match the power of a stock F-350? I would like a little more performance than the factory offers. Thanks for the help!
Brian Unruh
via email
Photo 5/7   |   Ford uses the same basic 6.7L Power Stroke engine architecture in all Super Dutys. However, chassis-cab F-450/5-50s don’t get the single sequential turbocharger, nor can they be easily upgraded to achieve the same power as the pickups—at least not legally.
ANSWER: As you note, Ford increased horsepower and torque for the 6.7L Power Stroke engine in ’18 F-250 and F-350s to 450 hp and 935 lb-ft of torque. The same engine in chassis cabs is rated at 330 hp and 750 lb-ft torque. The power difference lies in the engines having different turbochargers and, accordingly, unique ECM calibrations. The newest “light-duty” F-Series uses a dual-sided compressor wheel, also known as a single-sequential turbo, while the “medium-duty” F-Series is de-tuned by using a conventional fixed-vane turbo that flows less air. That accounts for a chunk of the chassis cabs’ power deficiency. As Ford’s “2017 Super Duty Chassis Certification vs. Dyno Certification” sheet notes, “The turbochargers are not directly interchangeable. In addition, the expense to change the turbocharger would be excessive and likely not worth the effort, as the vehicle still requires a dyno certification, which will produce lower ratings. Also, changing the turbocharger in the chassis cab would likely cause the vehicle to fall out of federal emissions compliance. Damages caused by this kind of alteration may void the engine and EGR system warranties.” According to the engine certification sheet, “All Super Duty pickups are chassis certified, which does not require exhaust gas recirculation at full power to pass the emissions test. Chassis cabs and medium-duty trucks are dyno certified, which does require EGR in order to pass the emissions test.” EPA guidelines allow trucks with 10,000- to 14,000-pound GVW to be either chassis or dyno certified. That’s why Ford (and its competitors) uses chassis certification for trucks in this GVW range, thus allowing them to show a 20 to 25 percent higher power rating than what dyno certification (required for trucks more than 14,000 pounds GVW) shows. So, short of running afoul of the federal smog laws, we’re afraid there aren’t many options to get the same power as found in the smaller light-duty F-Series pickups. ¬Tuning that increases the flow of the piezo injectors might be the only way to stay smog-legal and get a bit more horsepower.

Extend Truck Life

QUESTION: I would like to know your thoughts about types of improvements to make for a longer-lasting truck. My ’14 Chevrolet Silverado only has 12,000 miles on it. We purchased it new and use it to tow our fifth-wheel trailer. I am a longtime subscriber and see things like fuel lift-pump systems, downpipes, CP3 conversion kits, and such in the magazine. I change my oil every 5,000 miles and do the fuel filter at 10,000 miles. My goal is to make the truck as dependable as possible while we are on the road. Any suggestions would be greatly appreciated.
Bob Dudley
via email
ANSWER: Four things are critical for diesel longevity: Clean fuel, lubricants, coolant, and air. Installing a high-end lift pump that helps take the load off the stock fuel pump and maximizes the cleanest fuel (no water/particles) reaching the injectors is paramount. It also helps extend the life of the CP4 injection pump. Changing or draining those filters on a regular basis is also a big part of preventive maintenance. Perform oil service every 5,000 miles and start an oil-analysis program with the next change. Send the samples to a respected laboratory, then provide a sample at every third maintenance interval to keep an eye on what’s happening internally with the engine. Doing this alerts you to any usual wear issues. Use the best oil filter available. Flush the coolant system (including the block) every 40,000 miles, or every two years, which is probably twice as often as stated in the owner’s manual. It is good to change the transmission fluid and filter every 50,000 miles or three years, whichever comes first. We can’t stress enough how important clean fuel, lubricants, and coolant are to the life of a modern diesel engine. Change the air filter at least once a year—using a stock filter is fine. When downpipes and EGR coolers fail, replace them with aftermarket versions that have better welds, improved flow, and heavier material than OEM.

High Altitude MPG

QUESTION: I have an ’11 Ram. It’s stock with about 88,000 miles. I have only changed the airbox to an S&B Filters cold-air intake and Dynatrac lockout hubs. I have made two round-trips from Illinois to the West Coast, crossing over the big hills, and find that from about 6,500 to 9,200 feet altitude fuel mileage increases from 17 to 21.4 mpg on the computer, which I verified by the amount of fuel used and miles traveled. Do you have any ideas why there is a fuel-mileage disparity at higher altitude?
Bob Houlne
via email
Photo 6/7   |   Top Tech Tire Pressure Guage
ANSWER: Multiple reasons for altitude affecting fuel economy come to mind. The truck’s ECM could be programmed to use less fuel at those higher altitudes, because diesels operate with a wider air/fuel ratio range than gasoline engines’ optimum 14.7:1. Diesels love cold, dry air, too, so the gain you see could be from a more efficient fuel burn. Climbing mountains also means coasting down the other side. If you are relatively light on the throttle while climbing grades, the light use of throttle on the downhill side could be enough to boost the overall average to a higher mpg. How one drives has a huge effect on fuel economy. Drag also plays a role. At higher altitudes, the air has less drag on the vehicle, so it takes less power to maintain a certain speed at 6,000 feet elevation than it would at sea level. Tire pressure also contributes to better mpg at altitude; as the elevation climbs, so does tire pressure, which will be about 3 psi higher in that range of altitudes if ambient temperature is the same. The cumulative effect of all these can contribute to a boost in observed fuel economy.

O-Rings vs. Studs

QUESTION: I have an ’06 Dodge Ram 2500 with a 5.9L engine. I purchased and plan to install the revised ATS Diesel Performance Aurora 3000/Aurora 5000 compound-turbocharger kit with external wastegate. I have already installed Mads Smarty BBI Stage 1 injectors, a Hamilton Camshafts 178/208 cam with valvesprings and pushrods, and other supporting fuel mods. I also had ARP 625 cylinder-head studs put in and the head milled for flatness.
Photo 7/7   |   At less than 40 psi of boost, second-generation Cummins engines benefit from having the cylinder head O-ringed because their composite-style head gasket includes a fire ring around each cylinder. The multi-layered-steel head gaskets on later models can withstand higher boost without O-ringing the head.
I read the Diesel Power article on O-ringing and your answers to tech questions regarding O-rings. While I don't disagree that the modification helps (when done correctly), your recommending O-rings for boost pressure above 40 psi seems to conflict with your own advice. Most Diesel Power articles I've read typically have only recommended head studs for larger single or mild compound-turbo setups. The ATS website says, “When boost levels are more than 48 psi, head studs are highly recommended.” There is no mention of needing O-rings. Many online forum posts show plenty of engines making 60 psi and 600-plus hp using head studs only. The article in your July 2018 issue mentions the engine had 200,000 miles on it when the head studs were installed but doesn't say whether the head was checked for flatness or milled. If the head had been milled, would studs only be perfectly fine?
Regarding requirements for clamping the head, is there more that has to be factored in, such as head flatness, drive pressure, injection timing, and such? It would be nice to see an article that discusses the variety of root causes that can lead to head-gasket failures and when the variety of head mods are required. Also, are there any drawbacks to O-ringing? I know the issue with fire rings and heat cycles, but can O-rings have a similar issue? Does the head have to be retorqued? What about trucks that are subjected to very cold winter temperatures?
Brian Lumppio
via email
ANSWER: We sat down with Bill Allen, manager of Source Automotive and NHDRA competitor who did our O-ring work, and asked his advice regarding newer Cummins engines. “We would not O-ring the ’06 Dodge Ram 2500’s head. Under 40 psi of boost, from our own experiences, the second-generation trucks are the ones that benefit most from the O-ring addition. The newer engines have a multi-layered-steel gasket that does not include a fire ring around the cylinder (as were found in the ’94-to-’02 composite-style gaskets). The head we O-ringed was completely rebuilt and checked after the head-gasket failure. Prior to that, the gasket was replaced, but the head was not checked for flatness, as the owner was trying to save some money on the build. Would studs alone be fine? Not in my experience, especially with younger enthusiasts starting to purchase these trucks, and their unawareness of how to properly handle warm-up and such with a high-powered Cummins. I would always err on the side of more protection than none when it comes to the expense of losing a head gasket. Head flatness, injection timing, coolant pressures, and drive pressures all effect head-gasket longevity. Any issues with one or more of those can cause a failure. O-rings do not have the same heat-cycle failures as the fire rings do. We currently have a local customer with a ’95 Dodge Ram 2500 that makes more than 525 hp. The engine has been compounded and O-ringed since January 2011. He drives it daily for personal and work use, and to date he has experienced zero head failures. The head has been retorqued three times since initial head installation, and now we only see that truck for normal maintenance. Procedure for cold winter temperatures is the same as mild: Let the engine warm up before ripping out high boost numbers. Our rule of thumb is nothing over 20 psi of boost until we see a full thermostat cycle.”