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How to Keep an Old Diesel Truck on the Road

Rising truck prices and increased emission regulations have led thousands of diesel owners to hold onto their aging trucks rather than trade them in on newer ones. Given the fact that any Cummins, Duramax or Power Stroke can last well over 300,000 miles if properly cared for, we see no reason why this trend won’t continue in the foreseeable future. While we all know that nothing lasts forever, there are steps you can take to ensure your oil-burner continues to be reliable day-in and day-out for the next decade. By performing regular maintenance, choosing quality replacement parts and taking the proper precautions, you’ll be glad you opted for a truck that needs occasional TLC over one that calls for a hefty monthly payment.

So how do you keep your aging workhorse on the road and healthy? Believe it or not, common sense maintenance is the clearest path to longevity. After that, it comes down to replacing typical wear items such as brakes, U-joints and the occasional unit bearing when they’re needed. Depending on how familiar you are with your truck, its powertrain and whether or not you can turn a wrench, you can save yourself a lot of money over the long haul as well (think thousands). Beyond the basics, we’ll also explain why it’s wise to have your beefed up transmission gone through or your built engine freshened up from time-to-time. Your path to half a million miles starts here.

Always Observe the “Severe” Service Interval

Diesel Oil Drain Interval

It goes without saying that regular oil changes are paramount in keeping any engine alive, but in addition to keeping bearings, turbocharger(s) and the valvetrain happy, the engine oil employed in modern diesels has to deal with soot deposits, oxidation and nitration on a regular basis. On pre-DEF era engines such as the ’08-’10 6.4L Power Stroke, excess fuel injected on the exhaust stroke was used to light off the exhaust aftertreatment system to clean the diesel particulate filter. This drives the oil’s percent fuel content (PFC) up dramatically—and these engines are known to “make oil.” For these reasons alone, we would never observe a 10,000-mile oil change interval on any engine with all of its emissions equipment intact, unless an oil analysis told us otherwise. In our experience, it’s best to follow the manufacturer’s severe service interval, which is usually half of what the normal service interval states.

Quality Oil

Amsoil Signature Series 10W-30 Oil

While there is no shortage of engine oils to choose from in the automotive world, use the oil the engine manufacturer recommends or one that exceeds factory oil specifications such as Amsoil (its Signature Series 10W-30 is shown above). Always stick with the weight recommended by the OE, too. Your engine was designed, tested and intended to run on this oil, after all. The same goes for oil filter selection. Stay the course with AC Delco (Duramax), Motorcraft (Power Stroke) or Mopar (Cummins) products.

Miles vs. Hours

6.4L Power Stroke Oil Sludge

If your truck spends inordinate amounts of time idling, your oil changes need to be performed based on engine hours, not miles driven. Remember that one hour of idle time is equal to 25 mph, so if your truck idles just four hours a day that’s already 100 extra miles that isn’t showing up on the odometer. The photo shown above was taken from a 6.4L Power Stroke in a fleet of service trucks that’d been neglected for thousands of miles. Due to the high percent fuel content, soot deposits and other contaminants, the oil had turned to a tar-like sludge.

Trust the Factory

Ford Motorcraft Power Stroke Fuel Filters

Fuel is the lifeblood of the diesel engine and nine out of 10 issues are fuel-related. On top of that, today’s high-pressure common-rail fuel systems are expensive, costing upward of $10,000 to replace if a catastrophe occurs. You want to keep this investment protected at all costs—and that cost means forking over the cash for the best fuel filter and/or water separator. Here again, stick to OEM filters, and replace them every other oil change. Beyond that, also make sure you’re filling up at a high-traffic filling station that sees quick turnover in its diesel storage tanks.

Engine Wear Items

Diesel Engine Water Pump

There is a reason no life expectancy numbers exist on things like water pumps, pulley bearings, tensioners and serpentine belts. It’s because at any point after 100,000 miles they could be on borrowed time. Some go for a quarter-million miles while others barely make it to 90K. The same goes for radiator hoses, thermostats and especially coolant, which should always be changed or at least tested at the factory-specified interval (doing so will extend the life of your water pump, thermostats, radiator hoses and the like). As for front end accessory drives, idler pulleys, vacuum pumps, alternators and A/C compressors should be checked for bearing wear annually or any time you have the serpentine belt removed.

Driveline Wear Points

Cummins Ram Drive Shaft Nitto Ridge Grappler

Depending on how hard you are on your truck, you’ll need to keep tabs on wear parts like U-joints, carrier bearings and even ball joints. If you use your steed for lighter workloads, these components can last 200,000 miles or more. Either way, pay special attention to driveshaft vibrations, squeaks, popping or clunking over bumps (or when turning) and always be on the lookout for uneven front tire wear. Luckily, most factory driveline components are fairly stout pieces, but adding lifts, offset wheels and massive tires can increase their wear rate exponentially.

Glow Plug Upkeep

Diesel Glow Plug

Cold weather starts have always plagued diesels, but older trucks are especially susceptible to experiencing hard starts in frigid conditions. Aging glow plugs and glow plug controllers are usually the culprits and their lack of functionality only drains your batteries further when trying to fire up. Where applicable (Duramax and Power Stroke applications), it’s always wise to test your glow plug system each fall (or bi-annually), before winter hits. If you manage to get eight to 10 years of loyal service out of your glow plugs, replace all of them with fresh OEM units for peace of mind. As the tips age they become more brittle and on rare occasions break off and fall in-cylinder. Plus, after a decade of being tightened in place, breaking them loose in the heads is already dicey enough—don’t wait any longer...

Valvetrain Maintenance

Cummins Valve Lash Adjustment

If you’re keeping your Cummins or Duramax for the long haul, a periodic valve lash adjustment will be inevitable being that these valvetrains utilize solid lifters. For those still rocking the older, 12-valve 5.9L Cummins (’89-‘98), you should run the valves every 24,000 miles or 24 months (whichever comes first). Beginning with the 24-valve head Cummins (’98.5 on through the ’18 6.7L), that interval stretches out to 150,000 miles, or any time valvetrain components and injectors are removed for other repairs. For Duramax engines, the general consensus is to measure things at 100,000 miles and adjust if necessary (note that GM does not specify a specific interval). As for 7.3L, 6.0L and 6.4L Power Stroke owners, hydraulic lifters are in the mix so there is no need for valve lash adjustment.

Gauges Can Save You

Edge Insight CTS2 Monitor

While a lot of folks associate aftermarket gauges or monitors with adding performance, the two don’t always necessarily go hand-in-hand. For any diesel truck that tows, being able to see exhaust gas temperature, rail pressure, transmission temperature and even oil pressure can help you keep your engine in the safe zone and/or help you diagnose a drivability or performance issue. Edge Products’ Insight CTS2 monitor is one of the best ways to keep tabs on your truck’s powertrain. By connecting to the OBD-II port it can monitor everything the truck’s computer does (but we’ll note that EGT monitoring requires an additional accessory on some trucks).

On the high horsepower side…

Beefed-Up Transmission? Not So Fast

Allison 1000 Diesel Duramax Transmission

Just because you’ve built the Allison in your GM, the Chrysler automatic in your Ram or the four, five or six-speed in your Ford, it doesn’t mean you never have to think about your transmission again. With most diesel heads continually stacking horsepower on top of what they started with, the transmission that was originally spec’d to cope with a lower horsepower number is perpetually being tasked with a bigger workload. Even regular maintenance intervals can’t ensure a performance automatic lasts forever, especially if you frequent the drag strip regularly, hook to the sled or tow heavy. Remember, when a torque converter fails it sends everything throughout the rest of the transmission. Breaking the seal and inspecting things every two to four years can lead to catching a potential problem before it has a chance to get worse.

No Engine Is Ever Bulletproof

Duramax Diesel Piston Carnage

Built engines don’t last forever, either. Sure, they can handle much more abuse, but they won’t put up with excessive boost, high EGT and immense cylinder pressure indefinitely. Like a built transmission, it’s best to take a peek inside every once in a while to see if anything needs to be refreshed or upgraded. Finding something minor and addressing it before it turns into a catastrophe is much better than windowing a block, torching a piston or damaging a cylinder.

Fighting off rust is another never-ending battle for aging trucks. Find out how to win the war here.

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