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No matter what make or model of vehicle a company uses, the one thing that will impact how well it performs more than any other is the preventive maintenance (PM) schedule, and how it is enforced. Fuel efficiency, drivability, and safety are all impacted by the PM schedule, not to mention the total cost of ownership (TCO). But, PM schedules today are far different from those of 40, 30, or even just 20 years ago.

Here are some things that have changed, and what PM schedules look like today.

Building the Foundation

Whether 1963 or 2014, the foundation for preventive maintenance scheduling is the oil and filter change. The intervals that govern all other PM activity have nearly always been established using oil and filter change intervals.

For decades, this interval was between 5,000 and 7,500 miles for consumer use (12,000 miles per year or thereabouts), with an exception for what was called “severe use” — generally much higher annual mileage — in response to which the interval was reduced to 3,000 miles. Fleet use, up to double or more than the annual mileage accumulated by the typical consumer, fit that “severe use” definition, so the 3,000-mile oil change was a staple of the fleet PM schedule.

Time and technology began to change this beginning in the mid-1970s, with the introduction of the first American Petroleum Institute (API)-qualified synthetic motor oil, Mobil 1, and by the mid-1990s nearly every motor oil manufacturer featured synthetic products. The primary advantage these synthetic products provide is the maintenance of viscosity, particularly in cold weather, but also resistance to breakdown due to heat, friction, and chemical contaminants.

This led to changes in normal oil change intervals, lengthening them beyond the time-honored severe use 3,000 miles to 5,000 and more. But, not every fleet made this change. The price of synthetics was, and remains, higher than that of regular oil

What has changed further is that cars and trucks are simply better made, with better materials, than they were in the past, and thus do not require oil and filter changes as often. Thus, the combination of synthetic oil products and higher quality engines has made oil and filter change intervals longer than ever before.

Electronic Ignition: No More Tune-Ups

Beyond oil and filter changes, another standard part of a regular preventive maintenance regimen was the “tune-up.” Prior to the advent of the electronic ignition, a tune-up was usually recommended at 12,000 miles (once each year for consumers, twice for fleet use).

Standard items in this process were:

Ignition points (clean or replace).
Spark plugs (clean/regap or replace).
Condenser (replace).
Distributor rotor (replace).
Distributor cap (clean or replace).
Ignition timing (check and set if necessary).
Carburetor (adjust).
Those old enough to remember the “points, plugs, condenser, and rotor” days of engine tune-ups know that it was an important PM activity.

So, what has changed? Two primary technological advances — electronic ignition and fuel injection — have not only nearly eliminated the need for an engine tune-up, they have eliminated most of the items that tune-ups involved.

Prior to electronic ignition, the fuel/air mixture was ignited by a mechanical ignition. Put very simply, plug wires ran to the distributor cap, under which was the rotor. As the rotor turned, each plug was fed the spark as the rotor contact hit the distributor contact. It worked, and worked well when in tune; however, it was subject to wear that required the tune-up.

The electronic ignition eliminated the need for the ignition points, rotor, and distributor cap, and the adjustments and replacements thereof.

By 1975, the Detroit “Big Three” (Chrysler, Ford, and General Motors) made electronic ignition standard on all models. Today, the fuel ignition portion of a tune-up (as well as the parts associated with it), at least as a standard item in the preventive maintenance schedule, is a thing of the past.

For most of the life of the internal combustion engine (ICE), carburation provided the air fuel mixture needed to ignite in the engine cylinders, which, in turn, provided the power that ran the engine.

Again, to simplify a more complex device, the carburetor provides the mixture of air and gasoline that is needed in the cylinders, where it is ignited by a spark; the ensuing explosion moves the pistons, etc.

The mixture must be exact; if the mixture is too “lean” (too much air), the engine won’t run, or will run weakly. If the mixture is too “rich” (too much gasoline), the engine will run roughly. Tune ups included the adjustment of the carburetor mixture, as well as the choke (which provided extra fuel for cold weather starting).

The last carbureted vehicle sold in the U.S. was in 1990, and, since then, vehicles are equipped with fuel injection, first with “throttle body” fuel injection, followed by “multi-port” fuel injection.

Fuel injection provides far more accurate fuel/air mixture calibration, and does not require regular adjustment. The result is more complete and clean combustion and better fuel mileage.

Covering Other PM Items

Most PM schedules include other work, as well as various “checks” of systems. Here are some of these items that were checked, and whether they’ve changed over the years:

Transmission. It was generally accepted that, once per year, fleet vehicles should have the transmission fluid and filter screen changed. Transmissions create a great deal of heat via friction, and this heat (if it exceeds about 175 degrees Fahrenheit) can cause fluid to begin to oxidize, break down, and lose its lubricating properties.

Changing the fluid and screen at about 30,000 miles has always been a standard item of preventive maintenance. There are, however, automatic transmission fluids (ATFs) which the manufacturers claim will last up to 150,000 miles. While this may be true, performing this PM once or twice in the life of a typical fleet car is a great deal less expensive than an overhaul. This is as true today as it was decades ago.

Cooling System. Engines today contain a great number of aluminum parts, and aluminum needs the advanced corrosion protection that antifreeze provides. But, the primary job of the cooling system is, of course, keeping the system within an acceptable operating temperature, as well as adding to easy starting in extreme weather.

Fleets most often added a flush/fill PM to the schedule once per year (about 20,000-25,000 miles), and, again, this has not changed much in 2014. There are some coolants which are actually good for up to 150,000 miles; however, as with the transmission, a flush/fill each year (often as part of “winterizing” the vehicle) is much cheaper than repairing the damage overheating can cause.

One thing that has changed is that, rather than having to remove a radiator cap to check coolant levels (and to refill the system), cars today have plastic overflow tanks that make the process simpler (and safer).

Wheel Alignment. Also called “front-end alignment,” this PM item keeps the front wheels pointed properly and flat on the road. PM schedules over the years will have “check alignment” as an item; however, checking the alignment carries a cost with it. Most times, if front tires are wearing evenly, that is sufficient. Putting the vehicle on the alignment rack and checking the specs costs money. If tires show uneven wear (cupping, wear on one side, etc.) an alignment is needed and should be done. Brakes and rotors should also be checked for wear at this time.

Although front suspensions have changed over the years the three alignment measures — camber, caster, and toe in/toe out — remain the same today.

Checks. At each PM interval, most schedules both in the past and today will call for various “checks.” These will include checking all fluids (e.g., power steering, transmission, and brake) checking brake wear, and, as indicated previously, even checking the alignment.

New technology hasn’t yet replaced lubricating and hydraulic fluids, and so they remain an important part of any PM schedule.

One change has been the replacement of individual belts for the air conditioner, power steering pump, alternator, and other components with a single belt called a serpentine belt. Checking belt wear was then, and is now, an important PM activity.

Tire Rotation. Accepted as a normal, regular PM for decades, some experts say that tire rotation is simply a matter of preference. Rotating tires ensures that tires wear evenly. Front tires, particularly on front-wheel-drive vehicles, wear faster, as they are subject to greater stresses than rear tires.

Even tire wear permits the replacement of tires in sets of four. That said, some experts will say that provided individual tires are wearing evenly, that front tires wearing out sooner than rear tires is not a safety issue, and replacement of tires in pairs is perfectly acceptable.

Keep in mind, when tires are rotated they should be balanced and the wheel alignment performed, so this additional expense must be considered. Prior to the mid-1980s, most vehicles were rear-wheel drive and front tires were not subject to the same stresses as those on subsequent front-wheel-drive vehicles, which became more popular in ensuing years.