Automatic Transmission Fluid, The other oil change
After oil changes and cooling system flushes the fluid that is probably the next most important, if you have an automatic transmission, is the automatic transmission fluid. This is that magical red fluid that your transmission is completely incapable of functioning without. The engine will still run without oil and coolant, the steering system will still steer without power steering fluid, but the transmission will quit working altogether if it looses only a few quarts of ATF.
What is it
Automatic Transmission fluid is essentially a specialized hydraulic fluid. Like all other hydraulic fluids it’s primary task is to transmit force. The automatic transmission contains numerous hydraulic circuits that channel fluid force in order to activate hydraulic pistons and servos. These pistons and servos are responsible for actuating various clutches and other braking mechanisms in order to make the transmission function. ATF must also lubricate all of these mechanical parts that are constantly rubbing and touching and heating up against each other.
|Clean ATF is usually a nice red color|
In the past every vehicle had a second dipstick, other that the engine oil dipstick, which was used for checking the level of the ATF. For vehicles that are still equipped with such, checking the ATF is very easy. Most cars require that the engine be running with the transmission in park. Some require that the transmission be in neutral. Honda trucks and cars with automatics require that the engine be off. If you are not sure what your vehicle requires, you can sometimes find directions on the dipstick itself. If that doesn’t work then consult the owner’s manual.
Most cars also require that the engine and transmission be warmed up in order to get the most accurate reading. The reason for this is that ATF expands quite a bit as it warms up. One might believe the fluid level to be low when in reality the fluid is just cold. Many manufacturers put separate marks on the dipstick that are used if the fluid is cold, but what if the fluid is somewhere between cold and warm? This is why it’s just best to check it with the fluid warmed up.
The goal when adding or checking fluid is to make sure that the fluid level is between the two marks that are found on the dipstick. If the level is below the lower mark then some fluid must be added, but if the level is between the marks, then that is satisfactory, and no more fluid is required. If fluid needs to be added then usually it must be poured down the dipstick tube. These dipstick tubes that double as a filler tube are usually wide enough to put the end of a funnel into them. If the dipstick tube is too narrow to fit a normal sized funnel into the end of it, then there is likely a filler plug somewhere else.
|A tranny pan with a drain plug in it, the fill plug can be seen|
in the housing above the pan.
Many new cars do not have dipsticks. On these vehicles the fluid must be checked by climbing underneath the car and removing some kind of plug from the side of the transmission in order to see the fluid level. Some of these newer cars will still have the dipstick tube but no dipstick in it. On top of the tube you will find a plug that says in order to check the fluid level you have to take to take the car to the dealership service department. Once there, the technicians can check it with a special tool that looks just like a dipstick. This seems silly and it probably is. The reason for no dipstick is that the car builders want you to believe that you don’t need to check or maintain the fluid. Many of them actually say that the fluid they use is good for the life of the vehicle. This is not exactly true but with modern synthetic fluids, the fluid is at least good for the warranty period and that’s good enough for them. Some cars have a sensor in the transmission that will monitor fluid, and the level can be checked via the information computer located in the instrument cluster.
ATF Doesn’t Get Consumed
If you check your ATF regularly and find that you always have to add a little every few months then you have a problem. Transmission fluid does not get consumed as it is performing its job. Engines will naturally burn a bit of oil every time they are running which will cause the oil level to go down. Transmissions don’t burn fluid. If the fluid level drops it is most likely due to an external leak. Just because you don’t see puddle in the driveway doesn’t mean that there are no leaks. The only other place the ATF could go is into the coolant. The transmission fluid is pumped up to the radiator where it passes through a cooler that is located in the radiator, surrounded by coolant. If this cooler leaks it may allow transmission fluid to leak into the cooling system. This is very rare. Running the transmission low on fluid can be very damaging to the transmission. If the fluid is going away, find out where it is leaking and get it fixed.
Most of the time you can never go wrong following the manufacturer’s service recommendations, but when it come to ATF service there are a few things to consider. The thing that happens to just about every fluid in any automotive system is oxidation. When ATF becomes oxidized it is no longer able to perform its duties in an effective manner because it is no longer just pure ATF, it is some kind of oxide thereof. Think of the body panels on an old car. The rust that you see on an old car is oxidation of the metals that comprise that body panel. This oxidized metal is no longer good for maintaining the structural integrity of the car’s body panels. Oxidized ATF is the same way.
As mentioned previously, some cars supposedly come with ATF that is good for life. If this isn’t true then how can the ATF be serviced, and how often? The fluid can still be drained in the same ways that it is on older cars. There is always either a drain plug in the bottom of the transmission, or the pan that holds the fluid can be removed. Because these cars come with high quality synthetic fluid, this same fluid should be used when servicing such cars. The interval for this service will be fairly long, but it probably shouldn’t be ignored. If the supposed lifetime fluid were service every 80,000 to 100,000 miles, this would probably suffice.
|Transmission fluid drain plug in the pan. Above that the spin-on type|
fluid filter can be seen.
|The filter screen behind the transmission pan|