How do I check the transmission fluid level?

Always check the fluid level with the engine running (except Honda), the transmission in "park" (except Dodge products which should be in neutral with the emergency brake applied), and with the engine at operating temperature.   Remove the dipstick and wipe with a rag.  Insert the stick fully and remove.  Look at both sides of the stick to verify the same indication.  Repeat the process.

The reason to check both sides of the dipstick is that after the fluid circulates through the transmission, it dumps back into the pan area and will cause an agitation of the fluid.  This creates an uneven level and some fluid will "slosh" onto the stick and give a false reading.  Some transmissions are worse than others.

Another method of checking the fluid is to turn off the engine and immediately check the level.  This will stop the agitation and give an accurate level (no agitation) before the fluid in the torque converter has had a chance to drain back into the pan area which would give a false-high reading.

(Tip) If you have added fluid, go through the same procedure, but repeat the process several times before you look for a reading.  Some of the added fluid will adhere to the side of the filler tube and can give a false reading.

(Tip)  If the fluid level is low, you have a leak!  Transmissions do not consume fluid.  Have the leak diagnosed and repaired to prevent more serious problems.

After you have added fluid, drive the vehicle for a mile or two, then recheck the level.  This is especially important in front wheel drive vehicles.

I have a leak.  Can you tell me how much it will cost to repair it?

The real question is:  What is/are the source/s of the leak/s.  Most people can only see the bottom of the unit, and therefore conclude that the bottom pan gasket is leaking when, in reality, the leak is from above and running down and around the pan. Therefore, it is imperative that the unit be visually inspected to evaluate the leak situation!

So, the answer to the question is:  No, we can't without seeing the vehicle.

How long does a transmission normally last?

The is no accurate answer to that question.  The mileage or time of use before major problems occur will vary greatly, and therefore, we don't see a correlation between mileage and expected transmission failure.  It is not unusual that the first few years after a newly designed transmission hits the road, that early failures occur.  But, in later years with updates to the original design, the units become more reliable.  The three major factors in the life expectancy are periodic maintenance, maintaining proper fluid level, and driving habits.

Just like the dentist tells you, "Don't ignore them."  Check the fluid level and condition periodically, repair any leaks/problems promptly, service the unit on a regular basis, and add an auxiliary cooler if the vehicle is used for towing, commercial, or high ambient temperature climates.  Some units should have a shift kit installed.  Synthetic fluid may benefit some applications.  Check with your local ATRA shop for their advice to your specific application and needs.

Will it hurt to overfill the transmission?

In a word, no!  Although, it is possible that gross overfilling can cause the fluid to be subjected to moving parts and become aerated which could cause abnormal operation.  You may also notice leaks that ordinarily would not occur.

I have a computer controlled transmission and now the transmission is acting up.  What could it be?  Do I need a new transmission?

If you notice problems with your transmission, don't automatically assume that the problem is actually in the transmission.  Computers receive information from numerous sensors, process the information, and then signal/operate the transmission. Often, the problem is in one of the sensors, an electrical connection, or system ground. In such a case, any work on the transmission will not resolve the problem. Equipment called scanners can "read" the codes stored in the computer and help pin point the source of most problems.

Therefore, it is imperative that the entire control system be diagnosed before the transmission is attacked.  As the commercial says, "It's not you Father's Oldsmobile."

Most transmissions will not allow you to tow while using overdrive; You will be told to use the "normal" drive.  However, there are some that will let you tow in overdrive. This is a chance to use the vehicle operating manual to find the answer the overdrive question.  While you have the manual out, checkout the required service intervals, recommended tire pressures, etc.  This is a book that is often ignored, but is filled with valuable information.

This procedure involves attaching a small diagnostic computer to a terminal in your vehicle if your transmission is computer controlled. This device is then used to address your computer to determine if any trouble codes are present and to "read" the output from numerous electrical sensors that feed information to the computer. All of this information is useful in determining the integrity of the electrical control system for the transmission. Scanners have become very important in the diagnostic process.
Note: Expect a nominal charge for this service.

Also note:  When the computer "sees" any parameter from various sensors that do not fit established criteria, the computer will set a code for each error.  However, there are some errors that will be present that the computer will not sense because they are within the normal range but are not necessarily valid.  In that case, the system has to be diagnosed to determine if applicable sensors or other electrical components are performing incorrectly and creating an abnormal transmission operational response.

How often should I have the transmission serviced?

Normal service intervals will vary as a result of the use of the vehicle and the operating temperature of the transmission.  When you check the fluid level periodically, note how it smells.  You will notice a burnt smell long before the color changes.  And, when you notice a strong burnt smell, have the transmission fluid changed.  The mileage from the last service to now becomes your service interval.

Also, if there are lots of small bubbles in the fluid on the dipstick, it's time to change it.

The fluid life expectancy is directly related to the operating temperature of the transmission.  Normal operating temperature is about 215 degrees Fahrenheit, but the cooling efficiency of you vehicle's cooling system and the type of driving you do will be the real determinate of it's life expectancy.  At 215 degrees, it should go for 100,000 miles, but for each additional 20 degrees, the mileage is cut in half.

Should I drive in overdrive or normal drive?

When overdrive equipped vehicles fist came into the inventory, it was advised to not use the overdrive option while driving in town, but to use it when driving on highways.  This recommendation has been dropped as the history of problems with these units showed no relationship with failures due to in-town use of overdrive.

Therefore, you can use the overdrive position anytime.  However you may want the manually select the normal position when driving on highways in hilly terrain to avoid a "busy" shifting transmission especially while using cruise control.

A standard transmission is generally more fuel efficient that an automatic because the automatic needs a pump to produce pressure for the unit to work.  The pump takes some of the power from the engine to run.  Also, the automatic uses a torque converter to transmit power from the engine into the transmission, and is a fluid coupling and therefore does not transfer 100% of the power mechanically as a clutch in a standard will.  Later model automatics have a lock up torque converter that will provide a mechanical connection with the engine, but not in reverse and only in the gears above 1st.

Of course, driver technique will also play an important part in fuel economy.