Preventive maintenance is a necessary expense to keep your vehicle in good running condition. Following the scheduled maintenance recommendations in your owner's manual, checking fluid levels regularly and changing the fluids and filters periodically can minimize the risks of breakdowns and prolong the life of the engine, transmission, cooling system and brakes. So if you are driving a "maintenance challenged" vehicle, you need to pay closer attention to your fluids and filters.

Let's start with one of the most important fluids of all: motor oil. It not only lubricates the engine, but also cools, cleans and protects it. But the oil itself can't do all of these jobs without some help. Nearly half a pint of various additives are added to the typical quart of oil to improve the oil's ability to resist heat, friction, oxidation and contamination.

Short trip driving is especially hard on oil because the engine never warms up enough to boil off the moisture that accumulates inside the crankcase. The moisture comes from combustion gases that blowby the piston rings (the older the engine, the greater the amount of blowby). Most of these gases are removed by the Positive Crankcase Ventilation (PCV) system. But in a cold engine much of the moisture condenses and ends up in the oil. Water reacts with oil to form sludge and acids, and the result is accelerated engine wear.

The only way to get rid of the accumulated moisture, acids and sludge is to change both oil and filter. The filter only removes suspended solids such as dirt, carbon and metal particles -- not moisture, acids or sludge.

The oil and filter change intervals recommended by the vehicle manufacturers vary depending on the vehicle application and how the vehicle is driven. For "normal service" (which means mostly highway driving, NOT short trip city stop-and-go traffic driving), the scheduled maintenance intervals for changing the engine oil and filter range from 3,000 to as much as 7,500 miles, with the time interval being up to one year. Some vehicle manufacturers even say it is okay to replace the oil filter at every other oil change rather than every oil change.

But if you study the maintenance recommendations closely, most vehicles come under the "severe service" schedule, which generally calls for oil and filter changes every 3,000 miles or six months, whichever comes first. This is the same recommendation most aftermarket experts make. Severe service is short trip driving (7 miles or less, especially during cold weather), towing a trailer, or driving in dusty conditions.

If a newer low mileage engine is driven mostly on the highway, you can probably get away with the longer service intervals. But as an engine accumulates miles, it experiences more blowby which dumps more moisture and fuel into the crankcase. For this reason, engines with more than 70,000 miles should not use the extended oil change intervals regardless of how they are driven.

Some engines, such as diesels, suffer more blowby than others so they typically require more frequent oil and filter changes. For most passenger car and light truck diesels, 3,000 miles is still the recommended interval for all types of service.

Turbocharged engines likewise require more frequent oil changes because of the high temperatures encountered in the turbocharger bearings. A turbo can spin at tremendous speed (over 100,000 rpm in many instances). This, combined with the heat of the exhaust gases passing through the housing, creates an environment that accelerates oxidation of the oil. When the engine is shut off, for example, the temperatures inside the turbo bearing housing can soar to the point where it "cokes" the oil, forming hard black crusty deposits that can damage the turbo. Because of this, the recommended oil change interval for most turbocharged engines is 3000 miles or six months. The motor oil should be "turbo-approved" for such applications, or a synthetic motor oil.

Watch Check Oil Video
MOTOR OIL RECOMMENDATIONS

Regular oil and filter changes reduce engine wear and prolong engine life.

OIL FILTER MAINTENANCE

An engine's main line of defense against abrasion and the premature wear it causes is the oil filter. The oil filter removes solid contaminants such as dirt, carbon and metal particles from the oil before they can damage bearing, journal and cylinder wall surfaces in the engine. The more dirt and other contaminants the filter can trap and hold, the better.

In today's engines, all the oil that is picked up by the oil pump is routed through the filter before it goes to the crankshaft bearings, cam bearings and valvetrain. This is called "full-flow" filtration. In time, though, accumulated dirt and debris trapped by the filter begin to obstruct the flow of oil. The filter should be changed before it reaches this point because if the bypass valve is forced open, unfiltered oil will go to the engine.

Though many vehicle owner's manuals say filter replacement at every other oil change is acceptable, most professional technicians recommend changing the filter at every oil change. Why contaminate the clean oil with up to a quart of dirty oil? And why risk expensive engine damage if the old filter is on the verge of clogging up? A new oil filter is cheap insurance against premature engine wear.

Make sure you get the correct oil filter for your engine. In other words, follow the application listing in the oil filter supplier's catalog. Don't try to match filters by external appearances alone. Some filters have SAE threads while others have metric threads. Many overhead cam engines also require a filter that has an "anti-drainback" valve to prevent oil from draining out of the filter when the engine is shut off. This allows oil pressure to reach critical engine parts more quickly when the engine is restarted. Filters that are mounted sideways on the engine typically require an anti-drainback valve.

AUTOMATIC TRANSMISSION MAINTENANCE

Automatic transmission fluid is rarely changed for preventive maintenance, yet is often the cause of premature transmission failure. Considering how expensive a transmission is to replace, the cost of changing the fluid and filter periodically is peanuts.

Most vehicle owner's manuals do not specify a change interval for automatic transmission fluid, unless the vehicle is used for towing. The vehicle manufacturers say their fluids can go upwards of 100,000 miles under normal driving conditions. Yet most transmission experts say regular transmission fluid and filter changes every 25,000 to 30,000 miles can significantly prolong the life of the transmission. But if a transmission has a lot of miles on it and the fluid has never been changed, they also say it may be best to leave the fluid alone. Why? Because changing the fluid may loosen accumulated varnish deposits that could cause sticking of control valves in the valvebody.

At the very least, the transmission fluid level should be checked periodically. On most vehicles, this should be done after the vehicle has been driven and the fluid is hot. The dipstick is then read while the engine idling and the transmission is in park.

If the level is low, fluid should be added to gradually bring the level up to the full mark, but not overfilled (which can cause the fluid to aerate and foam). If the transmission is leaking fluid from the pan gasket or rear seal, these parts are not difficult or expensive to replace.

Very important! Make sure you get the correct type of fluid for your transmission. Refer to the owner's manual or markings on the dipstick if in doubt.

General Motors applications usually require Dexron II, Dexron IIe or Dexron III, or a fluid that meets these specs. Dexron IIe is required in newer electronic transmissions, and Dexron III is a long-life fluid that can also be used in older applications that require Dexron II or IIe.

Older Fords as well as some imports require Type F, but most newer Fords require Mercon or Mercon V. Mercon can also be used in older Fords that requires type H or CJ fluids (which are obsolete), but 1998 and newer Fords require Mercon V.

Chrysler typically specifies Dexron II for older automatics, but requires a special fluids that meet various Mopar ATF Plus specifications in its newer transmissions (ATF+2, ATF+3, ATF+4, etc.). Chrysler warns that using Dexron II or III in its newer transmissions can cause shudder and shifting problems.

Never open the coolant reservoir or radiator cap when the engine is hot.
COOLING SYSTEM MAINTENANCE

Brake fluid is another fluid that is usually neglected. The only time it is changed is when the brakes are relined (if then!). But it should be changed more often because brake fluid is hygroscopic and absorbs moisture over time. After two or more years of service, it can become badly contaminated with moisture. This lowers its boiling point up to 25% (which may contribute to pedal fade if the brakes overheat). It also promotes internal rust and corrosion that can damage calipers, wheel cylinders and antilock brake system components. Though most domestic vehicle manufacturers have no requirements for changing the fluid, European vehicle manufacturers as well as many brake experts say changing the fluid every two to three years for preventive maintenance can greatly prolong the life of the hydraulic components in the brake system and improve safety.

Changes aside, the fluid level should be checked periodically to make sure it is not low. The fluid level in the master cylinder will gradually drop as the brake linings wear, but a sudden drop usually means a leak and a possible loss of hydraulic pressure.

Make sure you use the correct type of brake fluid for your vehicle. Most domestic and Japanese passenger car and light truck applications require DOT 3 fluid, but most European and some domestic performance cars require higher temperature DOT 4 fluid. DOT 5 silicone fluid is not recommended for any vehicle with ABS brakes. Refer to your owner's manual, or look for a decal or markings on the master brake fluid reservoir or cap.

POWER STEERING FLUID

Like brake fluid, power steering fluid is hardly ever changed unless a hose fails or the steering gear has to be replaced. There is no recommended replacement interval for preventive maintenance, but the fluid should be replaced if the pump or steering gear has failed and is also being replaced. The old fluid may contain debris that can damage a new steering pump and steering gear. It is also important to check the fluid level in the pump reservoir periodically (a low fluid level usually indicates a leaky hose or seal somewhere in the system).

If fluid is needed refer to the vehicle owner's manual for the type of fluid that is recommended. Some require a special power steering fluid while others use ATF.

Use a bright shop light to inspect the air filter.
ENGINE MAINTENENACE: AIR FILTER

The air filter keeps dirt out of the engine, so its service life depends on its operating environment. Motorists who do a lot of driving on rural gravel roads may need a new filter every couple of months while the city dweller might go a year or more between changes.

To assure a proper fit, compare the old filter to the new one to make sure they are the same height and size. If the filter does not fit properly, unfiltered air may leak past it.

Another item that may be needed is a PCV breather filter, which is located inside the air cleaner housing on many vehicles. This filter should also be replaced if a new PCV valve is being installed.

Another air filter on many newer vehicles is the cabin air filter. This filter cleans the air that enters the passenger compartment. The filter's service life depends on its construction (dust only or dust and odor), and operating conditions. Dust only filters should be changed every couple of years, while dust/odor filters should be replaced yearly.

FUEL FILTER

For reliable engine operation and fuel system performance, a clean fuel supply is absolutely essential. The fuel filter is the fuel system's primary line of defense against dirt, debris and small particles of rust that flake off the inside of the fuel tank. If not trapped by the filter, such contaminants can plug fuel metering orifices in a carburetor or prevent valves from seating. In fuel injected engines, fuel debris can clog the injector inlet screens and starve the injector for fuel. And if debris gets inside the injector, it can wear or jam the pintle valve and seat.

With diesel engines, clean fuel is even more important because of the extremely close tolerances inside the injection pump.

The typical OEM recommendation today for fuel filter replacement is every 30,000 miles, but many professional technicians say yearly fuel filter changes can reduce the risk of dirty fuel-related problems.