If you read the fine print, however, you'll discover that the once a year, 7,500 mile oil change is for vehicles that are driven under ideal circumstances. What most of us think of as "normal" driving is actually "severe service" driving. This includes frequent short trips (less than 10 miles, especially during cold weather), stop-and-go city traffic driving, driving in dusty conditions (gravel roads, etc.), and driving at sustained highway speeds during hot weather. For this type of driving, which is actually "severe service: driving, the recommendation is to change the oil every 3,000 miles or six months.
For maximum protection, most oil companies say to change the oil every 3,000 miles or three to six months regardless of what type of driving you do.
A new engine with little or no wear can probably get by on 7,500 mile oil changes. But as an engine accumulates miles, blowby increases. This dumps more unburned fuel into the crankcase which dilutes the oil. This causes the oil to break down. So if the oil isn't changed often enough, you can end up with accelerated wear and all the engine problems that come with it (loss of performance and fuel economy, and increased emissions and oil consumption).
Regular oil changes for preventative maintenance are cheap insurance against engine wear, and will always save you money in the long run if you keep a car for more than three or four years. It's very uncommon to see an engine that has been well maintained with regular oil changes develop major bearing, ring, cam or valve problems under 100,000 miles.
WHAT ABOUT THE OIL FILTER?
To reduce the costs of vehicle ownership and maintenance, many car makers say the oil filter only needs to be replaced at every other oil change. Most mechanics will tell you this is false economy.
The oil filters on most engines today have been downsized to save weight, cost and space. The "standard" quart-sized filter that was once common on most engines has been replaced by a pint-sized (or smaller) filter. You don't have to be a rocket scientist to figure out that a smaller filter has less total filtering capacity. Even so, the little filters should be adequate for a 3,000 mile oil change intervals -- but may run out of capacity long before a second oil change at 6,000 or 15,000 miles.
Replacing the oil filter every time the oil is changed, therefore, is highly recommended.
An engine's main line of defense against abrasion and the premature wear it causes is the oil filter. The filter's job is to remove 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's 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. It's an efficient way of removing contaminants, and it assures only filtered oil is supplied to the engine. 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, which is why the filter needs to be replaced when the oil is changed.
If you wait too long to change the filter, there's a danger that it might become plugged. To prevent this from causing a catastrophic engine failure due to loss of lubrication, oil filters have a built-in safety device called a "bypass valve." When the pressure drop across the filter exceeds a predetermined value (which varies depending on the engine application), the bypass valve opens so oil can continue to flow to the engine. But this allows unfiltered oil to enter the engine. Any contaminants that find their way into the crankcase will be pumped through the engine and accelerate wear.
Oil consumption depends primarily on two things: the valve guides and piston rings. If the valve guides are worn, or if there's too much clearance between the valve stems and guides, or if the valve guide seals are worn, cracked, missing, broken or improperly installed, the engine will suck oil down the guides and into the cylinders. The engine may still have good compression, but will use a lot of oil.
An oil consumption problem caused by worn valve guides can usually be cured by a valve job. Knurling, sleeving or replacing the guides, or boring out the guides and installing valves with oversized stems will stop the loss of oil.
Oil can also get past the rings if the rings or cylinders are badly worn or damaged, if the cylinders were not honed properly when the engine was built (or rebuilt), or if the rings were installed improperly.
When a newly-built engine is first started, the rings require a certain amount of time to "seat" or break-in. If the rings fail to seat properly, the engine will use oil. This may be the case if somebody applied the wrong finish to the cylinders, failed to clean and lubricate the cylinders properly before the engine was fired up, or didn't use the proper break-in procedure.
If the rings and/or cylinders are at fault, the engine will have lower than normal compression readings.
In some instances, worn rod bearings, excessive bearing clearances and/or excessive oil pressure can splash too much oil on the cylinders causing oil to get past the rings.
The cure for worn rings and cylinders is to overhaul the engine block. The cylinders have to be refinished and new rings installed to regain good oil control.
Tightening the valve cover bolts or screws will rarely stop an oil leak because the gasket is usually cracked, crushed or has lost its natural elasticity. Cork gaskets only last about four to six years before they age harden, become brittle and start to leak. Molded silicone rubber gaskets, on the other hand, (which are used on many late model domestic and import engines) often last the life of the engine. But molded rubber gaskets are a lot more expensive than die cut cork gaskets. That's why cork gaskets have long been used by the vehicle manufacturers.
It might be wise to ask about a valve adjustment while the gasket is being replaced. Some engines require a valve lash adjustment at certain mileage intervals. You can save some money and the technician working on your car can save some time by providing this service while the valve covers are off the car.
Oil not only lubricates the engine's internal parts, but also helps cool the bearings. The total amount of oil in the engine, therefore, serves as a heat sink to help control heat. Under normal driving conditions, running a quart low probably doesn't make much difference in terms of bearing temperature or overall engine lubrication. But during extremely hot weather, when driving at sustained highway speeds and/or when towing a trailer, running a quart low may increase the risk of accelerated engine wear and/or damage.
The best advice, therefore, is to add oil whenever the dipstick reads low. Don't wait until it is down a full quart. If it needs half a quart, add half a quart to bring it back up to the full mark.
CAUTION: Do not overfill the engine. Adding too much oil can overfill the crankcase. As the crankshaft spins around, it can whip the oil into foam if the level is too high. This, in turn, can cause a drop in oil pressure and loss of lubrication to critical engine parts. Also, too much oil may cause leaks as the extra oil is forced past seals and gaskets.
For optimum protection, change the fluid and filter every 30,000 miles (unless you have a new vehicle that is filled with Dexron III ATF which is supposed to be good for 100,000 miles).
WHY ATF WEARS OUT
An automatic transmission creates a lot of internal heat through friction: the friction of the fluid churning inside the torque converter, friction created when the clutch plates engage, and the normal friction created by gears and bearings carrying their loads.
It doesn't take long for the automatic transmission fluid (ATF) to heat up once the vehicle is in motion. Normal driving will raise fluid temperatures to 175 degrees F., which is the usual temperature range at which most fluids are designed to operate. If fluid temperatures can be held to 175 degrees F., ATF will last almost indefinitely -- say up to 100,000 miles. But if the fluid temperature goes much higher, the life of the fluid begins to plummet. The problem is even normal driving can push fluid temperatures well beyond safe limits. And once that happens, the trouble begins.
At elevated operating temperatures, ATF oxidizes, turns brown and takes on a smell like burnt toast. As heat destroys the fluid's lubricating qualities and friction characteristics, varnish begins to form on internal parts (such as the valve body) which interferes with the operation of the transmission. If the temperature gets above 250 degrees F., rubber seals begin to harden, which leads to leaks and pressure losses. At higher temperatures the transmission begins to slip, which only aggravates overheating even more. Eventually the clutches burn out and the transmission calls it quits. The only way to repair the damage now is with an overhaul -- a job which can easily run upwards of $1500 on a late model front-wheel drive car or minivan.
As a rule of thumb, every 20 degree increase in operating temperature above 175 degrees F. cuts the life of the fluid in half!
At 195 degrees F., for instance, fluid life is reduced to 50,000 miles. At 220 degrees, which is commonly encountered in many transmissions, the fluid is only good for about 25,000 miles. At 240 degrees F., the fluid won't go much over 10,000 miles. Add another 20 degrees, and life expectancy drops to 5,000 miles. Go to 295 or 300 degrees F., and 1,000 to 1,500 miles is about all you'll get before the transmission burns up.
If you think this is propaganda put forth by the suppliers of ATF to sell more fluid, think again. According to the Automatic Transmission Rebuilders Association, 90% of ALL transmission failures are caused by overheating. And most of these can be blamed on worn out fluid that should have been replaced.
On most vehicles, the automatic transmission fluid is cooled by a small heat exchanger inside the bottom or end tank of the radiator. Hot ATF from the transmission circulates through a short loop of pipe and is thus "cooled." Cooling is a relative term here, however, because the radiator itself may be running at anywhere from 180 to 220 degrees F.!
Tests have shown that the typical original equipment oil cooler is marginal at best. ATF that enters the radiator cooler at 300 degrees F. leaves at 240 to 270 degrees F., which is only a 10 to 20% drop in temperature, and is nowhere good enough for extended fluid life.
Any number of things can push ATF temperatures beyond the system's ability to maintain safe limits: towing a trailer, mountain driving, driving at sustained high speeds during hot weather, stop-and-go driving in city traffic, "rocking" an automatic transmission from drive to reverse to free a tire from mud or snow, etc. Problems in the cooling system itself such as a low coolant level, a defective cooling fan, fan clutch, thermostat or water pump, an obstructed radiator, etc., will also diminish ATF cooling efficiency. In some cases, transmission overheating can even lead to engine coolant overheating! That's why there's a good demand for auxiliary add-on transmission coolers.
AUXILIARY COOLING
An auxiliary transmission fluid cooler is easy to install and can substantially lower fluid operating temperatures. The plate/fin type cooler is somewhat more efficient than the tube and fin design, but either can lower fluid temperatures anywhere from 80 to 140 degrees when installed in series with the stock unit. Typical cooling efficiencies run in the 35 to 50% range.
ATF FLUID TYPES
What kind of automatic transmission fluid should you use in your transmission? The type specified in your owner's manual or printed on the transmission dipstick.
For older Ford automatics and certain imports, Type "F" is usually required. Most Fords since the 1980s require "Mercon" fluid, which is Ford's equivalent of Dexron II.
For General Motors, Chrysler and other imports, Dexron II is usually specified.
NOTE: Some newer vehicles with electronically-controlled transmissions require Dexron IIe or Dexron III fluid. GM says its new long-life Dexron III fluid can be substituted for Dexron II in older vehicle applications.
CAUTION: Using the wrong type of fluid can affect the way the transmission shifts and feels. Using Type F fluid in an application that calls for Dexron II may make the transmission shift too harshly. Using Dexron II in a transmission that requires Type F may allow the transmission to slip under heavy load, which can accelerate clutch wear.
A typical fluid change will require anywhere from 3 to 6 quarts of ATF depending on the application, a new filter and a pan gasket (or RTV sealer) for the transmission pan. The pan must be thoroughly cleaned prior to reinstallation. This includes wiping all fluid residue from the inside of the pan and scraping all traces of the old gasket from the pan's sealing surface.
CAUTION: Do not overfill the transmission. Too much fluid can cause the fluid to foam, which in turn can lead to erratic shifting, oil starvation and transmission damage. Too much fluid may also force ATF to leak past the transmission seals.
Add half a quart at a time until the dipstick shows full. The transmission really isn't full yet because the dipstick should be checked when the fluid is hot, and the engine is idling with the gear selector in Park. So start the engine, drive the vehicle around the block, then recheck the fluid level while the engine is idling and add fluid as needed until the dipstick reads full.
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