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Changing Fluids, Filters, Belts & Hoses

Copyright AA1Car Adapted from an article written by Larry Carley for Import Car magazine

Though service intervals on today's cars are longer than ever before, they still require regular maintenance. That includes checking fluid levels, changing filters, and inspecting the belts and hoses.


Today's engines are capable of going 150,000 miles or more if the oil is maintained at the proper level and changed regularly. But many motorists never check their oil level, which increases the risk of running dangerously low if they put off having the oil changed too long or develop an oil leak.

Most engines should use very little oil (less than half a quart) in 3,000 miles. So if the dipstick is down a quart or more, it probably means that the engine is leaking or burning oil. Inspect the pan and cover gaskets, crankshaft seals and oil filter for signs of oil leakage. If none are found, you might recommend a vacuum test, compression test and/or leakdown test to reveal where the oil is going. In most cases, worn valve guides and/or seals are the main cause of oil burning, but worn or broken rings or worn cylinders may also be a factor.

OEM-recommended oil change intervals have been getting farther apart in an attempt to reduce maintenance costs for vehicle owners. But as some motorists have learned the hard way, stretching the oil change interval too far ends up costing them a lot more in the long run. Toyota, which has been recommending 7,500-mile oil change intervals for some time, has discovered that some engines are sludging up because the interval is too long.

Under ideal operating conditions, motor oil may go up to 7,500 miles or more between changes. But most operating conditions are less than ideal: short trips, stop-and-go city driving, etc. Moisture builds up in the crankcase and causes sludge to form. That is why the aftermarket continues to recommend oil and filter changes every 3,000 miles, particularly for older high-mileage engines that have more wear and blowby than new engines.

When changing oil, use the type and viscosity recommended by the vehicle manufacturer. Most newer engines should use 5W-30 oil. A few European models now specify 0W-40 synthetic. Overhead cam engines need a light viscosity oil to provide proper lubrication following a cold start. For older, high-mileage pushrod engines that have increased wear and clearances,

checking oil level on dipstick

10W-30 is probably the best choice. For warm weather performance or towing applications, 15W-50 may be the best viscosity.

Synthetic motor oils are a good upgrade for hard- working engines, and are required in some vehicles to meet OEM warranty requirements. Synthetics flow more easily than conventional oils at low temperature, and resist oxidation and viscosity breakdown at high temperature. Synthetics are expensive, so a blend may be a more affordable choice.


Another fluid that few motorists rarely check is the automatic transmission fluid (ATF) in their automatic transmissions or transaxles. If the dipstick reads low, the transmission is probably leaking. A low fluid level can cause delayed engagement, slipping and shift problems, and may contribute to premature transmission failure.

On most vehicles, the fluid level should be checked when the fluid is hot with the engine idling, the parking brake set and the transmission in Park. If fluid is needed, add only enough ATF to bring the level up to the full mark. Do not overfill because doing so can cause the fluid to become aerated, which may affect transmission operation.

You should also check the condition of the fluid. Some discoloration and darkening is normal as the fluid ages, but if the ATF is brown or has a burnt smell, it is badly oxidized and needs to be changed. Varnish on the dipstick is another indication of worn-out fluid.

You can also do a "blotter test" to check for worn-out fluid. Place a few drops of ATF on a paper towel and wait 30 seconds. If the spot is widely dispersed and red or light brown in color, the fluid is in satisfactory condition. But if the spot does not spread out and is dark in color, the ATF is oxidized and should be changed.

When adding ATF, use the type specified by the vehicle manufacturer. Honda, Mercedes-Benz and others all have their own specs for ATF. There is no such thing as a "universal" ATF that works in all transmissions. Some fluids meet a variety of specifications but cannot meet them all because of the different friction additives that are required.

Many transmission experts say that most transmission problems can be prevented by changing the ATF and filter regularly for preventive maintenance. How often depends on how the vehicle is driven. For some hard use vehicles, this might be every 30,000 miles or two years. For the average driver, changing the transmission fluid every five years or 50,000 to 60,000 miles would be beneficial.

The harder the transmission works, the hotter the fluid runs. The life of the fluid drops quickly once its temperature gets up above about 200 degrees F.

ATF also becomes contaminated with normal wear particles from the clutch plates, bushings and gears. The filter will trap most of this debris before it can cause problems. But many older Asian transmissions only have a plastic or metal screen that does little to protect the transmission against internal contaminants and nothing to keep the fluid clean. On these vehicles, changing the fluid is the only way to get rid of these contaminants.

checking engine coolant and belts


Check the coolant level, strength and condition. The coolant reservoir should be maintained at the full level, otherwise air pockets may form inside the radiator, which can cause cooling problems and overheating. If the level is low, the system should be inspected for possible leaks (hoses, radiator, freeze plugs, etc.). If there are no visible leaks, do a pressure test to check for internal leaks (leaky head gasket, cracked head or block).

The strength of the coolant should be adequate to provide freezing protection to the lowest anticipated temperatures for your area. A 50/50 mix of water and ethylene glycol antifreeze will normally protect down to -34 degrees F. If greater freezing protection is required, the mix can be increased up to 70 percent antifreeze, but no higher since straight antifreeze does not cool as efficiently as does a mixture of water and antifreeze.

The condition of the coolant is also important and should be checked yearly. If the coolant is discolored, contains sediment or is worn out (chemical test strips can reveal the level of corrosion inhibitor left in the coolant), it needs to be changed.

With traditional antifreeze, the recommended change interval is every two to three years or 30,000 miles. With extended life products, the interval may be 5 years or 100,000 miles (which ever comes first). For most vehicles, that means changing the coolant every five years - and not waiting until the coolant has 100,000 or more miles on it.

If the cooling system is dirty, use a cleaner to remove the harmful deposits and sediment. Then flush the system and refill with fresh or recycled coolant. Use the type of coolant recommended in your owners manual.

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A low fluid level in the power steering pump reservoir almost always indicates a leak. Inspect the hoses, pump and steering gear, and repair or replace as needed to fix the leak.

Under normal conditions, power steering fluid does not need to be changed. But it should be replaced if the pump or steering rack has failed to protect the new parts.

When adding fluid, use the type specified by the vehicle manufacturer. Do not use ATF unless it is approved for the steering system by the vehicle manufacturer.


The brake fluid level usually can be checked without having to open the fluid reservoir if the reservoir is transparent. But the condition of the fluid also needs to be determined because brake fluid absorbs moisture over time. Moisture contamination lowers the fluid's boiling temperature and breaks down its corrosion inhibitors.

You can use chemical test strips that react to contaminants in the fluid or its moisture content. Many brake experts recommend changing brake fluid every four to five years for preventive maintenance, and every time the brakes are relined or repaired. Use the type of brake fluid (DOT 3 or DOT 4) as required by the vehicle manufacturer (see your owners manual for details, or look at the markings on the master cylinder reservoir). Most European vehicles require DOT 4.


Though not a vital fluid in terms of vehicle operation, this fluid is vital for good driving visibility when bug splatter, dirt and road grime obscure the windshield. For cold-weather driving, a fluid that also includes deicer is a good choice to help melt ice on the glass.


The oil filter should always be changed when the oil is changed. The same thing applies to the filter inside the automatic transmission when the ATF is changed. But air and fuel filters are typically "replace as needed" items. A visual inspection of the air filter will reveal its condition.

Most fuel filters today are designed with sufficient capacity to last for a number of years, so follow the OEM-recommended replacement intervals, unless there is no recommended replacement interval for the fuel filter. For these vehicles, a new filter every two or three years should keep the fuel flowing freely.

On older vehicles, rust and other crud inside the fuel tank may cause the filter to plug. Replacing the filter may temporarily solve the immediate problem (no fuel), but cleaning or replacing the fuel tank may be necessary to keep the new filter from becoming plugged again.

On newer vehicles, cabin air filters also need to be regularly inspected and replaced. Cabin air filters keep odors and microscopic airborne particles out of the passenger compartment, so they are more of a comfort item than a performance item. Even so, a plugged filter can reduce air flow into the HVAC system, which may affect the performance of the air conditioner or heater.

Cabin air filters have been used on some import vehicles as far back as 1994, and are currently installed on about 40% of all new vehicles (mostly luxury models). The filters use activated carbon so they have a limited life. Replacement recommendations vary, but are typically 12,000 to 15,000 miles or once a year.

The cabin air filter is typically located under the dash or behind the glove box, but some are under the hood at the base of the windshield.

checking serpentine belt


Belts and hoses need to be inspected periodically to make sure they are in good condition. Replacement also may be recommended depending on the age and condition of the part.

Except for timing belts, which should be replaced every 60,000 to 100,000 miles (it depends on the engine), V-belts, serpentine belts and hoses are seldom replaced until after they fail (and they all eventually do fail). But waiting for the inevitable to happen is asking for trouble. Who wants to blow a hose or have a belt break out in the middle of nowhere? Either one can allow an engine to overheat, which cause additional damage and trouble.

You cannot always determine a belt's true condition by just looking at it. Any belt that is visibly cracked and frayed should be replaced. The same goes for belts that have missing chunks of rubber, are glazed or have been contaminated by grease or oil. But many belts that look as good as new on the outside have become dangerously weak on the inside and may be on the verge of failure due to weakened inside cords.

Belt manufacturers say the risk of V-belt failure rises sharply after three years of service, and four years with serpentine belts. Replacing V-belts every four to five years, or 40,000 to 50,000 miles, and serpentine belts every five years, or 50,000 to 60,000 miles, can minimize the risk of sudden belt failure and a breakdown.

Replacement belts must have the same width and length as the original. This is especially important with serpentine belts that rely on an automatic belt tensioner to maintain belt tension. The range of travel on most tensioners is very limited, so if a replacement belt is a couple of inches longer or shorter than the original, it may not work at all.

Belt tension is critical with both

V-belts and serpentine belts. It must be adjusted properly and maintained for good belt performance, quiet operation and long life. If a serpentine belt on an engine with an automatic tensioner has failed prematurely or appears to be slipping, the automatic tensioner should be inspected and replaced if it is sticking, frozen or has a broken spring. On applications that do not use an automatic tensioner, belt tension must be adjusted to specifications, then readjusted after a short break-in period.

Symptoms that would indicate a bad tensioner or idler pulley include bearings that clatter, a rumble or chirp sound when the engine is running, visible looseness in the pulley bearings, dragging or seized pulley bearings (the tensioner pulley should rotate freely), physical damage to the idler pulley wheel, arm or base housing, or belt squeal immediately after engine start up or when belt-driven accessories are under load.

Rubber hoses also need to be inspected because they deteriorate with age and exposure to heat. Tiny cracks develop in the rubber which eventually cause the hose to split, blister or leak. A hose also can fail from the inside out due to electrolytic corrosion within the cooling system. Some hose materials can actually become conductive under the right conditions, which causes the hose material to pit and weaken. Cracks and fissures tend to form near the ends of the hose that eventually eat through from the inside out. This type of deterioration can sometimes be identified by pinching the hose near each end. If ridges or voids can be felt in the hose, it means the hose is failing and should be replaced.

Hose manufacturers usually recommend replacing coolant hoses every four or five years to minimize the risk of hose failure. New clamps also are recommended to replace OEM ring-style clamps.

Finally, don't forget to check fuel hoses, emissions hoses and vacuum hoses. Replace any that are cracked, frayed, damaged or leaking.

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