Diesel Vehicle Service Requirements

Diesel power clearly has its positives as compared to gas-powered vehicles and many first-time buyers will join the ranks of diesel vehicle owners in the coming months/years. It is imperative that we understand the special service/operational requirements of these vehicles as opposed to gasoline power so we make no costly mistakes. In this column I will discuss the unique maintenance items that must be followed for owners of diesel vehicles.


Diesel engines do not require regular maintenance tuneups like gasoline engines because they have no electronic means of ignition. Spark plugs, ignition modules, spark plug wires and the likes are not used on diesel engines. However, they still require maintenance to optimize and maintain engine operation and longevity. The most important things to service on these engines are filters and fluids.

Engine oil: lubrication oil should be changed regularly with oil specified for diesel vehicles. If you’re looking to go the long haul (100,000 miles or more) with your diesel vehicle, you may want to replace your engine oil with a good quality synthetic motor oil like AMSOIL or Mobile One, Nos. 1 and 2 on the market, respectively. Synthetic motor oil minimizes wear of internal engine parts and bearings, maximizing engine life. Just make sure you follow the viscosity guidelines the manufacturer lies down for maximum flow rate.

Filtration: your vehicles’ owners or service manual will lay out filter changing intervals. Oil filters should be of the highest quality available. Diesel engines manufacture more ash and soot than gasoline counterparts, this dirt falls out and into the oil. It’s held in suspension for the filter to remove from the oil, if the filter is not of high quality, this dirt is left in the system to circulate and damage internal engine parts. Good filters remove small micron dirt, thus protecting the engine. Change oil filters every time you change the oil. Air filters must be kept fresh and clean. Since diesel engines rely on a strong, steady air intake for ignition and combustion, a fresh and voluminous air stream must be available to the engine at all times. Dirty air filters impede performance and economy, not to mention computer engine management systems, which are constantly making on-the-fly adjustments based on available airflow and volume. Follow the maintenance schedule for change intervals.

Fuel filter/water separator maintenance: diesels depend on the fuel itself for internal cylinder and injection pump lubrication, so it is critical for water to be filtered out as well as dirt. The function of water and other contaminant filtration is typically combined in a single filter on a diesel. The filter will have a bowl or other reservoir at its bottom, since water is heavier than diesel fuel and will sink to the bottom for draining. Diesel fuel filters have a valve at the bottom where water can be drained off. This is a simple matter of opening the valve until all the water has drained away, leaving only diesel fuel visible in the inspection bowl or in the stream released from the filter. Many cars are equipped with sensors and electronic valves that perform this function automatically, so the driver does not have to think about it. Check your owner’s manual for information on this.

Cooling systems: engine coolant battles rust and scale formation, acid buildup, foaming, silicate drop out and debris while it works to transfer heat and maintain engine operating conditions for optimal fuel economy. Regular coolant flushing and replacement is necessary to ensure optimum performance and longevity. Your carmaker will outline coolant drain intervals in the maintenance schedule. On some diesel engines, the cooling system uses a coolant filter to control the acidity (pH value) of the coolant. This filter ensures that the engine block does not build up rust and scale inside. Additionally, the filter releases anti-foaming compound and acid inhibitors offering added cooling system protection. This filter, like other filters needs regular replacement. Check owner’s manual for replacement intervals. Finally, there are some great coolant additives on the market that provide additional protection by maintaining nitrate levels, which aid in keeping rust inhibitors strong.

Fuel additives: there are many diesel fuel additives available, each formulated to give specific results. Some are intended as anti-gel compound in cold weather and others for injector cleaning or cetane boosting. Check your owner’s manual or with your dealer regarding what to use for different conditions. Remember that additives are just a maintenance step, additives cannot solve foundational problems like massive carbon and fuel deposit buildup. This must be addressed with professional cleaning procedures using special equipment and industrial strength cleaners. Federal regulation requires that ultra low sulfur diesel fuel be used to lower tailpipe emissions. While this helps, it also lowers fuel lubricity and poses a wear threat to expensive injection pumps and cylinder walls. I recommend using a lubricity additive for this reason.

Injector Maintenance: injectors often foul over time, which affects proper fuel spray pattern and can lead to increased emissions and carbon buildup as well as negatively affect power and fuel efficiency. There are a number of professional injector cleaning fluids which will effectively clean your injectors if they are not too dirty. If too dirty, have the injectors removed and professionally cleaned. If injectors are heavily cratered or pitted from corrosion, they will require rebuilding or replacement.

DEF Replenishment: diesel exhaust fluid is a fluid that is used to complete the cleaning up of exhaust emissions. It is stored in a separate tank located under the vehicle. The DEF tank fill point is located under the hood in close proximity to other fluids that need periodic maintenance, check your owner’s manual to find the location of the fill point. Your vehicle will display a light on the dash indicating the need to fill the tank when the tank gets down to a certain level. DEF shelf life is typically at least one year, depending on the storage temperature. It is best stored out of direct sunlight between 12 degrees and 86 degrees Fahrenheit. While DEF is not listed as a hazardous waste by the federal government, use proper disposal methods as it is a chemical. Do not empty into drains; dispose of this material and its container in accordance with all applicable local and national regulations.

Well, that should do it for special service requirements for diesel vehicles!

‘Til next time … Keep Rollin’

Tom Torbjornsen is an automotive expert of 38 years. An automotive journalist in good standing with the International Motor Press Association and Motor Press Guild, Torbjornsen has been the Repair and Maintenance editor for AOL Autos, At Home Portals, and many other websites. Hear his radio show AMERICA’S CAR SHOW, locally on AM1340 WKSN via the SSI Radio Network Saturday mornings at 8. See Tom’s television show, “America’s Car Show” on Buffalo’s all new WBBZ-TV, Channel 5 on Dish, channel 67 over-the-air and on DirecTV. The show airs weekly Wednesday nights 6:30-7. It is re-aired on Thursday mornings at 9 and Saturday mornings at 11. For more info on Tom Torbjornsen, visit AMERICA’S CAR SHOW website at: You can send Tom your car questions and TV show topic suggestions at: Find Tom’s book, “How To Make Your Car Last Forever” in local Barnes & Noble booksellers and online at