To flush or not to flush transmissions

To flush or not flush the automatic transmission? That is the question!

posted by Mark S

How a Transmission Flush Works
A transmission flush procedure is generally performed using equipment that either runs off the transmission pump or has its own pump built into the machine. The machines are connected to the transmission cooler lines, and while the old fluid is pumped out the new fluid is delivered at the same quantity and time. Sometimes there is a cleaning solvent that is forced back into the transmission removing deposits of old transmission fluid from parts and components or the technician performing the flush may run a solvent through the vehicles transmission before performing the flush. The cooling lines, cooler, converter and other parts are all thoroughly cleaned. One of the benefits of this procedure is that all of the transmission fluid is removed and replaced. This is different from a fluid change in which only some of the fluid is replaced. A simple fluid change cannot remove all of the built up deposits that accumulate over time as is done during a flush. Also, some of the fluid is usually stored in the torque converter potentially contaminating the new fluid that is put in. What is the point of that?
Transmission Flush Good or Bad?
I constantly hear consumer, customers and technicians debate as to whether transmission flush procedures can be harmful to a vehicle and is a transmission flush good or bad for your automobile. While many mechanics and experts agree that having a clean transmission will extend the life of a transmission, it is thought by some that the flushing procedure may not be the best way to achieve a clean transmission. One common thought is that the process, which forces liquid back into the transmission in the opposite way of the normal fluid flow, could potentially damage components or block tight passageways. When fluid is forcefully pushed back into the transmission, chunks of debris can be dislodged and possibly block narrow channels or one-way valves. When new fluid is put back in, these blockages can inhibit the normal flow of fluid through the transmission causing lubrication issues. Nonetheless, many car manufacturers and dealerships contend that these procedures are not harmful at all and help revitalize auto transmissions. MDH Motors does not use a reverse flush machine and over the thirteen years of being in the automotive repair industry I still yet to have seen a machine that flushes the fluid in reverse. Most machines just pump the new fluid in through the transmission cooler lines while containing the old fluid in a separate tank. The best transmission flush operation procedure is to:
1. Perform the transmission flush
2. Remove the pan and change the transmission filter
Doing the flush in this order while help prevent the possibility of contaminates going through your transmission and potentially causing a problem by, let’s say hanging up a valve in the valve body.
Checking your transmission fluid
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.
Many new cars do not have dipsticks. On these vehicles the fluid must be checked by climbing underneath the car and removing a 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. 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.
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 are found on the dipstick. If the level is below the lower mark then some fluid must be added, but if besides looking at the level the condition of the fluid can also be examined. If the fluid contains very tiny black particles that rub off on your oil rag or paper towel this is normal, but can it can indicate that the fluid needs to be serviced. These small black particles are bits of clutch pack material that are suspended in the fluid. This is a sign of normal wear and tear but if the particles become excessive, or if the particles are metallic looking; this could indicate some major problems. The last thing you can do that can help determine fluid condition is give it a sniff. Worn out fluid will have a definite burnt smell to it and fluid from a transmission that has completely failed smells downright disgusting.

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