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Car Maintenance: Why It Is Important

by Larry Carley copyright

Preventive car 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 5,000 to as much as 7,500 miles or more depending on the year, make, model and engine, with the time interval being up to one year.

Some vehicles use a maintenance reminder light rather than a mileage/time chart to recommend when an oil change is needed. When the reminder light comes on is determined by miles drive, hours of use, temperature and other variables. The PCM estimates remaining oil life, then turns on the reminder light when it estimates an oil change is due. Under ideal circumstances, the reminder light may not come on for up to 10,000 miles or longer. But these ultra long oil change intervals assume the engine is filled with a high quality synthetic motor oil (not a conventional motor oil).

Replace the oil filter every time the oil is changed. Some people think they can sa e money by replacing the oil filter at every other oil change. However, we would NOT recommend this because of the small capacity of most oil filters on late model engines. They are designed to be replaced at every oil change.

Regular Service or Severe Service Oil Change Intervals?

If you study the car maintenance recommendations closely, the type of driving that many vehicles are subjected to is actually "severe service", 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 extremely dusty conditions (such as rural gravel roads).

If a newer low mileage engine is driven mostly on the highway, you can probably go with the longer "normal" service intervals. But as an engine accumulates miles, it experiences more combustion blowby past the rings which dumps more moisture and contaminants fuel into the crankcase. For this reason, engines with more than 75,000 miles should not use extended oil change intervals regardless of how they are driven.

Some engines, such as diesels, suffer more blowby than others due to their higher compression ratio, so they typically require more frequent oil and filter changes. For most passenger car and light truck diesels, 3,000 miles is a good recommendation for all types of service. Diesels also require motor oil that is certified for diesel use. Current specifications call for an API service rating of CK-4 (2017 and newer light duty diesel engines) or CJ-4 (for 2010 to 2016 model years).

Turbocharged engines also 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 also be "turbo-approved" for such applications, or a high quality synthetic motor oil.

maintenance neglect


What type of oil should you use? Most vehicles today are factory-filled with 5W-20 or 5W-30 because thinner viscosity oils improve cold starting, fuel economy, and allow the oil to reach critical upper valvetrain components in overhead cam engines more quickly than heavier viscosity oils. Some engines also specify ultra-thin 0W-20 or 0W-40 oils for the same reason.

CAUTION: Use the viscosity of motor oil recommended by the vehicle manufacturer for your engine. Many late model engines have Variable Valve Timing (VVT) and require a specific viscosity of motor oil to function correctly. If a heavier viscosity motor oil is used, it may affect the operation of the VVT cam phases that alter cam timing, causing the engine to set a fault code and turn on the Check Engine light. For more information about oil viscosities, Click Here.

Equally important: Make sure the motor oil meets the performance requirements for your engine. Different vehicle manufacturers have different performance standards for motor oils. Most quality oils will perform adequately in most applications. However, there are exceptions. GM says oils that meet their Dexos requirement must be used in late model GM engines. Most European auto makers have their own special oil specifications. Make sure the oil you use meets or exceeds those specifications.

As a rule, synthetic motor oil will usually outperform conventional motor oils due to the higher quality base oils in the product. Synthetics are more expensive, but provide superior hot and cold temperature performance compared to petroleum based conventional motor oils. They are especially good for turbocharged and high output engines. Switching to a synthetic motor oil for easier cold weather starting can help you winterize your car. Synthetic oils also experience less viscosity breakdown over time. That is why synthetic oils are essential for extended service intervals of 7,500 miles or longer.

High mileage motor oils are another option for older vehicles with more than 75,000 miles on the odometer. These oils contain more detergents and seal conditioners to help keep older engines clean and leak-free.

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


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.

Make sure you get the correct oil filter for your engine. 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 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 for late model vehicles do not specify a change interval for automatic transmission fluid, unless the vehicle is used for towing or it has a Continuously Variable Transmission (CVT). 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 50,000 miles can significantly prolong the life of an automatic transmission.

If your transmission has a lot of miles on it (say 100,000 or more) and the fluid has never been changed, it's probably best NOT to change the fluid. Why? Because changing the fluid may loosen accumulated varnish deposits that could cause sticking of control valves in the valvebody.

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.
NOTE: Some late model vehicles do not have a dipstick for checking the fluid level inside the transmission. There may be a filler plug on the transmission itself that can be removed to check the fluid level.

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. Using the wrong fluid can cause transmission problems and possible transmission failure!

For specific ATF fluid recommendations, Click Here.


check coolant
Never open the coolant reservoir or radiator cap when the engine is hot.

The antifreeze in the coolant performs three very important jobs: it prevents the coolant from freezing during cold weather, it raises the boiling temperature of the coolant to prevent overheating during hot weather, and it fights corrosion.

Besides checking the level of the coolant periodically to make sure it isn't low (which usually indicates a leak), the strength and condition of the antifreeze should also be checked. Most vehicle manufacturers recommend a 50/50 mixture of water and antifreeze for normal freezing and boil over protection. Up to a 70/30 mixture of antifreeze and water can be used to maximize freezing protection, but higher concentrations should not be used because antifreeze does not cool as effectively as water. A Up to a 30/70 mixture of antifreeze and water can be used in hot climates to improve cooling efficiency. Straight water or straight antifreeze should never be used in a vehicle's cooling system.

Determining the condition of the coolant is a little more difficult because appearances alone can be deceiving. If the coolant is brown and discolored, it is obviously long overdue for a change. But even if it is still green or orange or yellow, there's no way to tell how much corrosion protection is still in the coolant without measuring its "reserve alkalinity." This can be done with chemically-treated test strips that give a good-bad indication by color changes.

If the cooling system is low and needs additional coolant, make sure you use the correct type of coolant or a type that is compatible with the coolant that is already in the system.

Most vehicle manufacturers recommend changing green coolant every two to three years or 30,000 miles to replenish the corrosion inhibitors in the antifreeze. Longer-lived orange and yellow coolants have a recommended service life of 5 years or 150,000 miles. If the cooling system is dirty, use a flush to remove rust and scale.

Starting in 1996, new General Motors vehicles were factory-filled with a new 5 year, 150,000 mile long-life coolant called "Dex-Cool." The coolant is dyed orange to distinguish it from ordinary antifreeze. If it is intermixed with ordinary coolant, the corrosion inhibitors can react reducing the corrosion protection to that of normal coolant (2 to 3 years or 30,000 miles).

Long-life aftermarket antifreezes can also be used in older vehicles to extend the coolant change interval to five years or 150,000 miles.

For the environmentally conscious, you can also get antifreeze that is propylene glycol based. The main difference is that it is less toxic than ordinary ethylene glycol antifreeze (reduces risk of accidental poisoning if the cooling system leaks and an animal licks it up).


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.


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 car maintenance service interval, 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.

check air filter
Use a bright shop light to inspect the air filter.


The air filter keeps dirt out of the engine, so its service life depends on its operating environment. Typical factory recommended replacement intervals for engine air filters are 30,000 to 50,000 miles. However, motorists who do a lot of driving on dusty rural gravel roads may need a new filter every couple of months. It all depends on how quickly the filter becomes dirty.

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 air filter on many newer vehicles is the cabin air filter. This filter cleans the air that enters the passenger compartment. It is usually located behind the glovebox or under a panel at the base of the windshield in the cowl area of the engine compartment.

The cabin air filter cleans the air before it enters the HVAC unit and 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 two years or 20,000 miles. Odor-absorbing filters should be replaced yearly or every 12,000 miles. More frequent changes may be required depending on operating conditions.


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 filter also separates water from the fuel to protect the injectors and pump from corrosion.

Most late model vehicles with gasoline engines have "lifetime" fuel filters that are located inside the fuel tank with the fuel pump. There is no recommended service interval for these types of fuel filters.

Vehicles with diesel engines, however, have an in-line filter and/or fuel/water separator. Most have a recommended service interval of 24,000 to 30,000 miles.

Older vehicles with gasoline engines that have an in-line fuel filter typically have a recommended service interval of 30,000 to 50,000 miles. NOTE: Replacing an in-line filter with quick-lock couplings requires a special tool to release the couplings. Trying to pry the fuel lines apart from the filter will damage the lines.

To keep your fuel injectors, throttle and intake manifold clean, and to reduce the buildup of carbon deposits on intake valves, pistons and inside the combustion chamber, use a Top Tier gasoline, or add a bottle of fuel system cleaner to your fuel tank every 3000 miles. Special cleaner products and fuel additives can be used to remove existing carbon deposits (follow the directions on the product for how to use the cleaner.

Need Factory Recommended Service Information for Your Vehicle?

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(Online factory service information for all vehicles)

AAA Survey Reveals Most Common Car Maintenance Problems

A survey conducted by AAA found that dirty air filters are the most common car maintenance problem. The AAA survey of member clubs also revealed several other common preventive maintenance problems:

Low Tire Pressure Tire pressure should be checked at least once a month to ensure tires are not under or over-inflated. Tires pressure levels should match recommended levels in the owner's manual. Low pressure in the tires can increase wear and fuel consumption. Having too much pressure may reduce traction. Keeping tires properly aligned will also help ensure longer tire life and improve fuel economy.

Worn Wiper Blades Rigid, cracked or torn wiper blades can greatly reduce visibility when driving in rain and snow. Wiper blades should be examined and replaced once a year or sooner if streaking occurs.

Low or Old Engine Oil Old and dirty oil reduces engine protection and increases engine wear, while low oil levels can lead to overheating. If the oil level drops too low, lubrication will be lost and severe engine damage can result. Regular oil changes (based on the schedule suggested in the owner's manual) will extend engine life.

Old Transmission Fluid Changing automatic transmission fluid at the intervals recommended by the vehicle manufacturer will keep the vehicle shifting smoothly and extend the life of the transmission. Take your vehicle to a shop that uses a transmission flusher to exchange new fluid for the old. This does a much more complete job than a simple drain and fill.

Low Coolant Level and Weak Antifreeze The coolant level should be maintained at the full mark on the reservoir, and the strength of th4e antifreeze should provide freezing protection down to -25 degrees Fahrenheit.

Worn Tires Minimum tread depth should be 3/32 inch. Tires should be replaced if the wear bars are flush with the surface of the tread.

Car Care Survey Finds Neglected Car Maintenance an Ongoing Problem

Motorists are keeping their vehicles longer than ever before, but they are also not maintaining them properly according to the care care maintenance inspection results by the Car Care Council. Here's what they found:

car care maintenance inspection results

Why Motorists Put Off Needed Repairs

A survey by of 1,200 motorists in the U.S. revealed the top 10 most ignored car problems and why people put off having the problems repaired:

Top Ignored Car Problems

Read the full report and survey results HERE,

Preventive Car Maintenance Resources:

Recommended Service Intervals from the Car Care Council

AA1Car Preventive Maintenance Guideline Chart

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