Smooth Sailing

Improper oil drain intervals can be the cause of turbo bearing trouble. While most owner-operators change oil more frequently than engine makers’ common recommendations of 15,000 to 25,000 miles, it’s wise to check maintenance records or to get oil analysis when acquiring a used truck.

Engines can act up because of the failure of some tiny component or deterioration in any number of places. Here are some common engine problems and the maintenance techniques that can keep you out of trouble.


One of the most common unit injector troubles results from a problem in a related system. Symptoms such as a gradual reduction in power output, normally without a lot of smoke, and a drop in fuel economy can be traced to failing to adjust the overheads – the closest thing there is to a tune-up on a heavy-duty diesel.

The overheads are adjustable rocker levers that operate the injectors and valves via the camshaft. After a lot of wear, the position of the injector will not be in the right relationship to the camshaft.

“You won’t be using the full travel of the injector,” says Doug Wilson, a Caterpillar analyst. The result is a lack of atomization of the fuel and reduced fuel delivery that you experience as a loss of power and fuel economy.

Engine makers require an adjustment of the overheads after the initial break-in period and then normally at infrequent intervals, especially on the latest engine models. Wilson says Caterpillar recommends doing them between 15,000 miles and 60,000 miles or after the third oil change. After that, go to 300,000 miles.

Peter Blonde, drivetrain engineer with Volvo Trucks of North America, says Volvo recommends an initial adjustment after three to six months or 50,000 miles. After that, the interval moves to 150,000 miles to 175,000 miles and 18 months.

Detroit Diesel’s national service manager, Gene Walker, recommends an initial adjustment at 60,000 miles to 100,000 miles. “After that, it does not tend to change,” he says. “If fuel economy and performance are good, the adjustment is likely OK.”

Cummins’ Zack Ellison, director of technical support, recommends the interval listed in the owner’s manual. Not only do intervals differ between engines with in-block camshafts, like the N14 and those with overhead cams like the ISX/Signature, but Cummins has made modifications that have lengthened the intervals in recent years.

Wilson says it’s hard to find misadjusted valve overheads, and when they are out of whack, “the symptoms don’t exactly jump out at you.” While wear in the mechanism can result in noisy valves that restrict air and exhaust flow, the most common wear pattern is valves that pound into the head and get too tight. This can result in overheating and burning.

Adjusting the valve overheads along with the injector rockers at recommended intervals will not only maintain engine performance and economy, but it will also prolong valve life.


Experts say it’s critical to buy filters that meet the micron rating for your particular engine and to change filters at the specified interval. The recommended micron rating relates to the clearance between the injector plunger and body. Particles that exceed the rating will get trapped between the surfaces and score them.

Ellison says the rating for a Cummins N14 differs from the ISX requirement. Wilson says that with the wrong filter, the clearance between the plunger and bore will increase more quickly than normal. The result will be a “loss of fuel delivery rate” because too much fuel will leak back around the plunger during injection.

There is also normal injector wear, say Blonde and Walker. At 26,000 psi to 30,000 psi injection pressure, the tiny nozzle holes erode and become slightly larger. “This means you get more fuel than the computer is allowing for,” says Blonde. Walker points out that you also lose atomization. There will, of course, be smoke; due to poor combustion, you may have a lack of power. Blonde says this is a normal condition after 600,000 miles to 700,000 miles, if you’ve been using good filtration. (Poor fuel filtration can cause premature nozzle erosion.) Today’s injectors are normally replaced with remanufactured ones rather than being rebuilt in a local shop. Reman injectors will put you back on the road at full power.


Like the canary used to warn miners of bad air, the turbo bearing will warn you first of engine lubrication problems. That’s because it’s “the most sensitive bearing in the truck,” Walker says. After all, the turbo turns at 100,000 rpm and up. Blonde says turbo bearing trouble often results when owners “cheat on oil change intervals.”

How to spot such trouble? “Make sure there are no excessive oil leaks into the charge air cooler from worn turbo bearing seals,” says Blonde. If you see leakage, check for clogging of the turbo drain line, which contributes to the leakage. Walker says you may see smoke, the boost gauge will show a little less pressure, and, “The pitch of the sound made by the turbo may change.” It’s all a result of high soot level in the oil.

Most owner-operators change oil more frequently than necessary, but if you’re looking at buying a used truck, don’t assume it had frequent drains. Extending changes is a good idea, as long as you use the right oil and filters and regular oil analysis.

Walker mentions air intake leaks on the suction side of the turbo as another problem. A typical leak occurs “when the hood rubs a hole in the rubber boot,” though leaks at clamps or elsewhere are just as common. Debris or dust can easily cause “sandblasting of turbo compressor blades.” Again, symptoms are low boost pressure and, often, smoke. Water that works its way into the intake system during rainy weather can do the same thing. Make sure intake grills and hoods are properly mounted and air-tight.


“Always buy fuel from a known source,” Blonde says. “Be aware of the difference between summer versus winter fuel and don’t use blended fuel unless you need it. Fuel must have the right energy level or you’ll lose performance, and blended fuel has less.” He recommends fuel heaters and careful use of anti-wax additives and the like, especially those containing alcohol, until conditions get extreme.

Blonde also suggests using a good fuel-water separator – preferably one with a sight glass that shows accumulated water. Drain frequently. Keep enough fuel in your tanks to minimize condensation in winter. The Davco separator supplied by Detroit Diesel indicates a clogged filter when the bowl fills up, Walker says. Water in the fuel can literally blow the tip off an injector.

Fuel cetane rating is critical. High cetane fuel ignites much more readily at cold temperatures, minimizing cranking and raw-fuel contamination of engine oil. Good ignition quality helps minimize knock and soot even right after cold starts, helping performance and noise level and keeping your engine young.

Cummins’ Ellison says low (rated less than 42) cetane fuels “will result in performance problems – white smoke and stumble during acceleration may result.”


Experts recommend filter changes based not only on restriction gauge readings, but also on time and miles. Why? Some impurities can accumulate without creating much of a restriction, yet still threaten the health of the filter. Also, Wilson says, the gauge doesn’t hold the maximum reading, meaning high restriction only at certain times can be a problem even when it’s not indicated. Caterpillar’s Wilson recalls how a trucker and his dealer were going crazy with a problem that emerged only at full throttle. Finally they discovered a poor quality air cleaner whose pleats would fold over one another and restrict air flow at full throttle. The lesson: Buy quality parts.

Dust that gets through can destroy not just the turbo but also the entire engine. Wilson suggests checking inside elbows with a white rag, looking for dirt that may have leaked in. If necessary, double clamp joints, turning the clamps 180 degrees apart.

Periodically clean the charge air cooler fins carefully to remove air-blocking debris. Dirt here will reduce the amount of air the engine ingests by interfering with cooling. Also check the many seals where the tubes join the headers for air flowing out – leakage here is a common problem.


Many electronics problems are prevented the old-fashioned way – by poking around the engine compartment and fixing the common things that plague all electrical systems. Blonde suggests careful attention to the ground straps that connect the engine to the cab. If the voltage supply to the electronic control module and the ground aren’t right, low voltage can cause poor ECM performance. Also check voltage-bearing connectors, such as alternator connector studs or ECM connectors, for intact wiring and insulation, and clean, tight connections. Use dielectric grease inside electrical plugs to prevent corrosion. The same goes for all sensor connections on the engine.

Walker says good maintenance of connectors and mounting clips keeps wiring from shifting and vibrating. Replace them if they break. Check for places where wiring may have rubbed against something or gotten pinched or frayed, compromising insulation. You should get the electronics checked even if the check-engine lamp flashes for only a second. When you get a red light, stop until you find the problem, as you can easily damage the engine if you continue.

If trouble crops up, “shooting” it often comes down to one of these steps: simple interpretation of codes via a card (as with Detroit Diesel); use of an inexpensive Palm Pilot handheld computer to read and interpret codes (Cummins); or taking brief electronic snapshots with the ECM (Caterpillar) when the engine seems to be acting strangely. A review of your owner’s manual or a brief discussion with your engine dealer should simplify troubleshooting.


Coolant will be working a lot harder with the cooled exhaust gas recirculation systems of the post-Oct. 1 engines, so if you have a new engine, maintain its coolant carefully.

With the Volvo system, Blonde says the clamps must be replaced when there is any sign of leakage. Don’t attempt to tighten.

For Cummins’ cooled EGR system, the variable geometry turbo is adjusted via air pressure that’s controlled through an electronic valve. Complete electrical troubleshooting would probably be best left to a technician. But even on an exotic system like this, simply inspecting the connector pins to make sure they are intact and clean can help keep the system working right. The system has a turbocharger control shutoff valve that has its own spin-on air filter. Replacing such items at recommended intervals will keep the system, which enhances engine performance while enabling the exhaust to recirculate, working as it should.

The variable geometry turbo systems have different boost pressure characteristics that may at first appear to be erratic. Don’t suspect engine trouble unless there is an obvious loss of performance, an electronic code warning or a consistent change in operating characteristics.

Use quality air filters and mount them carefully so they won’t leak. Low-grade filters can cause intermittent running problems that are hard to find.

Common symptoms of engine problems and their usual causes:


  • Reduced airflow, normally accompanied by reduced boost pressure readings. Often accompanied by smoke, except on the latest engines.
  • Clogged or defective air cleaner (sometimes indicated by restriction gauge).
  • Defective turbocharger (worn bearing or damaged blades).
  • Leaking air intake system (pressure side between turbo and engine) – especially hose connections or charge air cooler.
  • Dirty aftercooler – especially clogged fins.
  • Overheads far out of adjustment (improper unit injector timing).
  • Worn injector plungers (normally from dirty fuel and without smoke).
  • Poor quality fuel or use of No. 2 fuel blended with No. 1.
  • Lack of fuel supply due to restriction in fuel system on suction side, especially clogged filters (may be indicated by restriction gauge or check engine light/appropriate code).
  • Air in fuel due to leak on suction side of pump – defective seal at hose or filter connection, leaking hose, defective filter canister or seal, leaking fuel filter restriction gauge. In rare cases, porous fuel filter mounting casting.
  • Restriction or improperly positioned tank selector valves on fuel system return side, resulting in lack of cooling of fuel.
  • Improperly installed unit injector, allowing exhaust leak into fuel.
  • The latest electronic engines may reduce fuel flow when reduced boost pressure is sensed, so the only symptoms of inadequate air flow will be lack of power and low boost pressure, with no smoke.

  • Clogged, dirty or defective air cleaner.*
  • Worn injectors (typically only at high mileage – normal long-term nozzle erosion).
  • Low cetane or impure fuel (white smoke and stumble during acceleration.)
  • Malfunctioning turbo (accompanied by low boost pressure).*
  • Leaking air intake system (pressure side between turbo and engine) – especially hose connections, charge air cooler or intake manifold.
  • Dirty aftercooler – especially clogged fins.*
  • Clogged fuel filter (slow response and white smoke).
  • Severe engine wear, normally accompanied by high lube oil consumption.
  • High backpressure due to
    dirty exhaust system, muffler problem, use of inadequate
    muffler for the power rating or uprating of engine without exhaust system modifications.
  • If confined to a brief puff after throttle increase, and the engine has a hydromechanical fuel system, the injection pump requires recalibration due to lack of maintenance or tampering.

  • Low cetane fuel (late and irregular ignition).
  • Significant amount of air in fuel due to leak on suction side of pump – defective seal at hose or filter connection, leaking hose, defective filter canister or seal. In rare cases, leaking fuel filter restriction gauge or porous fuel filter mounting casting.
  • Engine running cold due to malfunctioning thermostat (especially in cold weather).

  • Defective check valve in fuel system, allowing filters to drain during shutdown.
  • Low cetane fuel (late and irregular ignition).
  • Air in fuel due to leak on suction side of pump – defective seal at hose or filter connection, leaking hose, defective filter canister or seal. In rare cases, leaking fuel filter restriction gauge or porous fuel filter mounting casting.
  • Severely worn engine (low compression).

  • Stretching oil change intervals too long. Often clogs turbo drain line, leaving telltale signs of oil leakage in air intake system.
  • Leaking air cleaner seals or connections on suction side of air cleaner in intake system. Dust erodes compressor blades.
  • Failure to maintain cooling system properly (water-cooled turbo). Failure to idle engine for at least three minutes for turbo cooldown after coming off the highway.