Regardless of the type of transmission your vehicle has, checking the transmission fluid should be part of your maintenance routine.
- The bad news is… one type of transmission makes things a bit more complicated.
- The good news is… You probably don’t have that transmission.
Just like your engine has oil to lubricate and carry away heat from its internal parts, automatic transmissions have specially formulated fluid to do the same.
Automatic transmissions, dual-clutch automatic transmissions, and continuously variable transmissions all rely on a certain type of transmission oil.
If you do not know which fluid your transmission takes, check the owner’s manual. Typically, there will be a section with technical specifications that includes the requirements for transmission fluid.
Keep reading and you will learn how to check your transmission fluid, how often to check yours, and what to look for in the fluid itself.
How To Check Transmission Fluid?
The process is normally a five-step process. This sequence gives you a general idea of how it is carried out.
#1. Park Your Vehicle On A Level Surface, And Start The Engine.
Typically, the engine should be running at the normal operating temperature when checking the transmission fluid level.
If the transmission is cold, you will not have an accurate reading. The vehicle should be in the correct gear (PARK, or NEUTRAL) on solid, leveled ground.
#2. Open The Hood And Identify The Transmission Fluid Dipstick.
Typically, the dipstick is located close to where the transmission or transaxle interfaces with the rear of the engine. The dipstick looks similar to the oil dipstick.
#3. Remove The Dipstick.
The fluid within the tip should be covered in transmission fluid all the way to the FULL line indicator. If the fluid level is low (it does not rise to the FULL line indicator), you can simply top it off.
#4. Inspect The Fluid.
Insert the tip of your index finger and sample the fluid on the dipstick, rub the fluid between your finger and the tip of your thumb.
The transmission fluid on the dipstick should be a pinkish color and almost clear. If it is dark, smells burnt, or has particles in it, let a mechanic drain and change the fluid.
#5. Check The Level.
Use a clean, lint-free rag to wipe the dipstick; put the dipstick back, and then remove/inspect again. Check the fluid level, which is how high the fluid rises on the dipstick, against the marks on the dipstick that say “full” and “low”/”fill.”
If the transmission fluid is clear, but does not reach the “Full” line on the dipstick, use a funnel to pour down the dipstick tube just enough new transmission fluid by itself to reach the line. Do not overfill!
Checking Automatic Transmission Fluid
Most major automakers recommend replacing automatic transmission fluid between 100,000 miles and 150,000 miles. If you are unsure, you can check your owner’s manual for your vehicle manufacturer’s recommendation.
However, if you were to ask 10 professional mechanics how often they would change your transmission fluid, the overwhelming majority would probably tell you the interval for changing the transmission fluid should be much sooner.
Regardless, you should routinely check the level (and condition) of automatic transmission fluid, regardless of how often you change it. If your transmission has a dipstick and filler tube, you can check the fluid level yourself. If the transmission does not have a dipstick and filler tube, you should have a mechanic inspect your transmission fluid for you.
A few tips to evaluate the condition of your automatic transmission fluid:
- Always check the level of transmission fluid when the engine is at normal operating temperature.
- If you check the level with the engine cold, you will get an inaccurate reading. The majority of cars should have the engine running during this process; however, check your owner’s manual.
Check Fluid Level
You should always check the fluid level first. Using the dipstick, check to see if the automatic transmission fluid level is between the “add” and “full” indications on the dipstick.
If it falls between the two, then the fluid level is normal. If the level is on “add” or below, the fluid level is below and needs to be replaced. A low fluid level will make the transmission much slower to engage, and if the fluid level is too high, air can mix with it and cause all sorts of problems with shifting. You will also experience a lot of sounds and slippage.
You should check the fluid level if the transmission is overheated. Just put the car in park and let the engine idle.
Before you check the fluid level, change the shifter to all of the gears. This will give you a much better reading.
Check Fluid Condition
If the transmission fluid is foamy or has a lot of little bubbles, it means there may be too much fluid in the automatic transmission. It might also mean you have a plugged transmission vent or you are using the wrong type of fluid in the transmission.
Transmission fluid that is brownish in color could mean that there is contamination with coolant. There may be a leak in the radiator’s fluid oil cooler, which is mixing the transmission fluid with the coolant. You should fix this problem immediately if you see this.
Check Fluid Color
You can check to see if the fluid has oxidized by just smelling it or by performing a blotter test. Get a clean paper towel and put a couple of drops of automatic transmission fluid on it. After about 30 seconds, look at what color the fluid is and how it diffuses out.
If it has diffused out and looks light brown, pink, or red, the fluid is in good shape. If it has not diffused and is dark brown, it means you have fluid oxidation. Therefore, you should flush or change the fluid directly.
How to Add Automatic Transmission Fluid
If you have checked the fluid level in the transmission of your vehicle and it is low, but you need to add more fluid, follow these simple guidelines:
- Always consult your owner’s manual and find out what automatic transmission fluid is required by your vehicle.
- Once you have purchased several quarts of the specified fluid. You can always keep any unused fluid for future fluid changes. Or you can return any unopened containers to your parts store for a refund.
- You should have followed the steps to check the transmission fluid according to the specific procedures for your car. The owner’s manual should provide sufficient guidance, see above under ‘check automatic transmission fluid’.
- If the former fluid level was low, the transmission dipstick indicates nothing about how much to add to the transmission. You do not want to overfill the transmission, so start off by adding ½ quart.
- After the initial amount of fluid has been added, check the transmission again using the checking procedure. If the dipstick reveals the transmission is now full, you’re done. Wipe the dipstick clean and insert it back into the transmission.
- If the transmission requires adding more oil, again, add a little amount and repeat the checking procedure. Keep repeating and checking until the oil level reaches the upper mark.
Note: Some newer model cars do not offer a dipstick to check and add automatic transmission fluid. If this is the case for your particular vehicle, you will have to involve your dealer or preferred mechanic to check and add transmission fluid periodically.
Check Your Manual Transmission Fluid
Manual transmission fluid (or gear oil) is used to lubricate and cool the manual transmission.
Anytime your vehicle has issues shifting gears or if you hear grinding noises while shifting gears, you should find out whether or not your transmission fluid is at the proper level.
Regardless of having had issues, it’s good to know how to check all the fluid levels regularly in order to avoid damaging your transmission if, for some reason, the fluid goes bad or becomes low.
A dipstick would make it easy to check manual transmission fluid levels, but unfortunately, most manual transmission vehicles do not have one. This means if you want to check the fluid, you will have to get the ”filler plug” and check the level of fluid yourself.
You can take off the filler plug by turning it counterclockwise, it is located on the side of the transmission, though some transmissions have it located on top.
If necessary, make sure to raise the transmission with a jack or ramp of some sort in order to locate the filler plug and check the level of fluid.
Once the filler plug is removed, you will see your transmission fluid and a hole to check the level of fluid. You can use your finger to check the level of fluid if the owner’s manual says that’s okay.
While you are checking the level of fluid, look closely at its color and smell. If the color is dark and has a burnt smell, it needs to be replaced. There should also be no metal parts in the fluid, either.
How to Add Manual Transmission Fluid
If you checked your vehicle’s manual transmission, you may discover that the level of transmission fluid is low and needs to be added. Perform the following steps to add fluid:
- Identify and obtain the specific type of transmission gear oil you will need based on your owner’s manual.
- Get several quarts of this specific oil, noting that while you can save the unused oil for later, if your containers are unopened, you should be able to return them for a refund.
- You will also need a transmission fluid hand pump, available at your parts store. The pump will screw into the fluid container and come with some length of plastic tubing to insert into the fill port for adding oil.
- You will find that the gear oil will become thicker and have more viscosity when cold. Cold oil can be difficult to draw with the hand pump you purchased. It will be best to store your transmission gear oil cans inside your home until you are ready to add oil to your manual transmission or warm them in a bucket of hot water (but do not leave them unattended!).
- Check the level of the transmission gear oil following the recommendation method for your car (see ‘Check Manual Transmission Fluid’ above). It is unlikely that your owner’s manual will have this procedure documented. A shop manual for your specific vehicle may help with this and various additional services.
- Install the pump into the gear oil container. Insert the plastic tube into the fill port of the transmission. Pump the handle several times to add fluid into the transmission until the level reaches the fill port.
- Remove the plastic tube from the fill port, wipe clean the fill plug, replace it into the fill port, and tighten snugly.