Fleets with newer vehicles that follow manufacturers' service recommendations often go 500,000 miles without needing an overhaul, and those that add low-micron bypass filters like the Como, Gulf Coast, or Harvard, coupled with regular oil analysis, often achieve that life with half the oil changes.

A good preventive maintenance program is more than just a regular lube-oil change-filter (LOF) replacement. At least twice a year trucks should get specialized maintenance; summerizing in the spring and winterizing in the fall are when the extras should be done.

Here are some tips to get you through the harshest weather:

Replace lube oil and change filter. Choose the right viscosity oil for the climate. For most of the United States, and for general operations, 15W-40 oils for diesels are fine. If you are in the northern tier of states or Canada, you might want to try 10W-30. It will stand up to the rigors of a modern diesel and offer occasional warm-weather performance almost as well as 15W-40.

For engines left out in below-zero temperatures, fully synthetic 5W-40 oil will flow easily on startup better than any mineral-based oil. It also gives year-round protection better than any mineral oil.

For warmer weather, some fleets go back to 15W-40, but just as automobiles now use thinner oils like 5W-20, diesel engines can get by with 10W-40 CJ4 oils. Beyond oil selection, preparation for summer should involve the same maintenance as winterizing.

Oil drain is the cornerstone of a good preventive maintenance program, but there's far more to it. Some trucks, especially older and heavier ones, need chassis greasing between LOF intervals.

Check/change coolant. When winterizing and summerizing, check and, if needed, change antifreeze coolant. Modern glycol coolants are mixed with water, generally in a 50/50 ratio. For extreme cold, increase glycol to no more than 60%.

Water is an outstanding cooling medium, but it has major drawbacks. Tap water contains minerals that form scale that insulate, causing uneven cooling. Buy premixed coolant or mix with deionized water.

Water is also prone to cavitation on cylinder liners — that's the process that forms bubbles. When the bubbles collapse, the implosions will, over time, punch holes in medium- and heavy-duty engines' cylinder liners. Special supplemental coolant additives coat and protect liners. Organic-acid technology long-life coolants generally do not need these additives. They are good for five years; longer if fortified with boosters and not diluted with ordinary coolants.

Evans Waterless Coolants avoid water problems. They have a much lower freezing point and a higher boiling point. Without water, there is neither cavitation nor resultant liner pitting.

Pressure-test your radiator cap and cooling system. With water-mixed coolants, check the radiator cap for proper pressure. Each pound increase raises water-mixed coolant's boiling point by 3° F. A 50/50 mix boils at 223° F. With a 15-psi radiator cap, it stays liquid to 268° F, continuing to provide cooling.

If you need a new cap, have it pressure-tested, too. There are far too many counterfeit parts, and radiator caps and thermostats are among the most popular knock-offs.

Test your thermostat by boiling a pot of water and use a cooking thermometer to check that it opens when it should. Check your fan clutch for proper operation. Heavy-duty fans consume 55 hp or more, so you want yours off as much as possible.

Check batteries and the charging system. Check belt tensioners and fan belts. Tensioners can drag and glaze belts, reducing alternator rpm. Many a battery has been replaced when it only needed a good charge, and many an alternator has been replaced when it only needed to be driven at full speed.

Batteries can be drained by short circuits caused by damaged wire. Snow and ice control chemicals are the archenemy of truck electrical systems, so be sure all wire is protected, especially at connections. Use shrink-tube over splices and paint open connections with vinyl “liquid electrical tape.”

Clean your HVAC system. You'll need heat and air conditioning to dehumidify air for defrosters. Clean any debris from cab heat exchangers and make sure the HVAC system is working well. Clean all the truck's heat exchangers: radiator, oil cooler, and air conditioner condenser.

Keep air brakes dry. In winter, eliminate moisture from air brake lines and tanks so it doesn't freeze. Ice can block air lines and crack brake valves. Change desiccant cartridges in compressed air systems.

It's these special seasonal tasks that set winterizing (and summerizing) apart from ordinary preventive maintenance. They take extra time, but the time is minimal compared to downtime for repairs, and the cost is insignificant compared to the cost of a road service call and the loss of productivity from crew and vehicle.

— Paul Abelson ( is a former director of the Technology and Maintenance Council of the American Trucking Associations, a board member of Truck Writers of North America, and active in the Society of Automotive Engineers.

  • Replace lube oil and change filter.
  • Check/change coolant.
  • Pressure-test your radiator cap and cooling system.
  • Check batteries and the charging system.
  • Clean your HVAC system.
  • Keep air brakes dry.